query: what are the rings on an atom called

pos: Electron shell Electron shell In chemistry and atomic physics, an electron shell, or a principal energy level, may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the " shell" (also called "K shell"), followed by the " shell" (or "L shell"), then the " shell" (or "M shell"), and so on farther and farther from the nucleus. The shells correspond with the principal quantum numbers ("n" = 1, 2, 3, 4 ...) or are labeled alphabetically with letters used in the X-ray notation (K, L, M, …). Each shell

neg: Spiro compound type. Bicyclic ring structures in organic chemistry that have two fully carbocyclic (all carbon) rings connected through just one atom are present both in natural products, as well as in esoteric targets of chemical synthesis. The two carbocycles can be different in nature, or identical. In common targets derived from natural products, they are essentially always different. In esoteric targets, such as highly strained hydrocarbons like spiropentadiene, shown here, the rings can be identical. The atom connecting the two rings is called the "spiro-atom"; in carbocyclic spiro compounds, the spiro-atom is a quaternary carbon. The 11-carbon bicyclic structure shown above,

neg: Heterocyclic amine heterocyclic ring. These molecules are unsaturated and contain a nitrogen atom in the ring. Four pyrrole rings are joined in a ring structure called a porphyrin. The rings of porphyrin are components of hemoglobin, myoglobin, vitamin B12, chlorophyll, and cytochromes. In the centers of heme in hemoglobin, myoglobin, and cytochromes, iron is an ion; in the first two, iron ion is bound to oxygen. The structure of pyridine is similar to that of benzene except that a nitrogen atom replaces one carbon atom. Pyridine is used as a flavoring agent. The pyridine ring is part of two B vitamins: niacin

neg: Atom (Ray Palmer) to restore the natives of Kandor to their full height, but is instead tricked into reviving a twisted Kryptonian cult, whose leader proceeds to crush Palmer and Kandor. Other re-imaginings of the Atom include an appearance in "League of Justice", an Elseworlds story portraying the Justice League in a "The Lord of the Rings"-type story where the Atom was recast as a wizard/fortune teller called "Atomus The Palmer". In "", Ray Palmer worked with a science consortium whose members at one point included Thomas Edison and Nikola Tesla. In "JLA: Rock Of Ages", the Atom is part of what remains

neg: Zirconocene Zirconocene Zirconocene is a hypothetical compound with 14 valence electrons, which has not been observed or isolated until now. It is an organometallic compound consisting of two cyclopentadienyl rings bound on a central zirconium atom. A crucial question in research is what kind of ligands can be used to stabilize the CpZr metallocene fragment to make it available for further reactions in organic synthesis. In contrast to the sandwich compound ferrocene with the cyclopentadienyl rings bound on opposite sides of a central metal atom, zirconocene and other group 4 metallocenes are bent. Without stabilizing ligands, the CpZr fragment is unstable

neg: Prelog strain ion leaves the cyclic molecule. This study fits the general trend seen above that rings with transannular strain show increased reactions rates compared to smaller rings in S1 reactions. The regioselectivity of water elimination is highly influenced by ring size. When water is eliminated from cyclic tertiary alcohols by an E1 route, three major products are formed. The semicyclic isomer (so-called because the double bond is shared by a ring atom and an exocyclic atom) and the (E) endocyclic isomer are expected to predominate; the (Z) endocyclic isomer is not expected to be formed until the ring size is large

neg: Spiro compound compounds. Spiro compound A spiro compound, or spirane, from the Latin "spīra", meaning a twist or coil, is a chemical compound, typically an organic compound, that presents a twisted structure of two or more rings (a ring system), in which 2 or 3 rings are linked together by one common atom, examples of which are shown at right. The simplest spiro compounds are bicyclic (having just two rings), or have a bicyclic portion as part of the larger ring system, in either case with the two rings connected through the defining single common atom. The one common atom connecting the

neg: Spiro compound Spiro compound A spiro compound, or spirane, from the Latin "spīra", meaning a twist or coil, is a chemical compound, typically an organic compound, that presents a twisted structure of two or more rings (a ring system), in which 2 or 3 rings are linked together by one common atom, examples of which are shown at right. The simplest spiro compounds are bicyclic (having just two rings), or have a bicyclic portion as part of the larger ring system, in either case with the two rings connected through the defining single common atom. The one common atom connecting the participating

neg: Basic aromatic ring atoms, e.g. imidazole and purine. In non-basic aromatic rings the lone pair of electrons of the nitrogen atom is delocalized and contributes to the aromatic pi electron system. In these compounds the nitrogen atom is connected to a hydrogen atom. Examples of non-basic nitrogen-containing aromatic rings are pyrrole and indole. The basic aromatic rings purines and pyrimidines are nucleobases found in DNA and RNA. Basic aromatic ring Basic aromatic rings are aromatic rings in which the lone pair of electrons of a ring-nitrogen atom is not part of the aromatic system and extends in the plane of the ring. This

neg: Zirconocene and synthetically challenging organic structures can be realized by novel C-C coupling of nitriles. Zirconocene Zirconocene is a hypothetical compound with 14 valence electrons, which has not been observed or isolated until now. It is an organometallic compound consisting of two cyclopentadienyl rings bound on a central zirconium atom. A crucial question in research is what kind of ligands can be used to stabilize the CpZr metallocene fragment to make it available for further reactions in organic synthesis. In contrast to the sandwich compound ferrocene with the cyclopentadienyl rings bound on opposite sides of a central metal atom, zirconocene and

neg: Basic aromatic ring Basic aromatic ring Basic aromatic rings are aromatic rings in which the lone pair of electrons of a ring-nitrogen atom is not part of the aromatic system and extends in the plane of the ring. This lone pair is responsible for the basicity of these nitrogenous bases, similar to the nitrogen atom in amines. In these compounds the nitrogen atom is not connected to a hydrogen atom. Basic aromatic compounds get protonated and form aromatic cations (e.g. pyridinium) under acidic conditions. Typical examples of basic aromatic rings are pyridine or quinoline. Several rings contain basic as well as non-basic nitrogen

neg: Carbohydrate to form a hemiacetal or hemiketal, forming a heterocyclic ring with an oxygen bridge between two carbon atoms. Rings with five and six atoms are called furanose and pyranose forms, respectively, and exist in equilibrium with the straight-chain form. During the conversion from straight-chain form to the cyclic form, the carbon atom containing the carbonyl oxygen, called the anomeric carbon, becomes a stereogenic center with two possible configurations: The oxygen atom may take a position either above or below the plane of the ring. The resulting possible pair of stereoisomers is called anomers. In the "α anomer", the -OH substituent

neg: Bridged compounds Bridged compounds A bridged compound is a chemical compound, generally an organic compound, but also possibly inorganic, that has two or more rings (a ring system) that contains a "bridge"—a single atom or an unbranched chain of atoms (or even just a valence bond) that connect two "bridgehead" atoms. The bridgehead atoms are defined as any atom that is not a hydrogen, and that is part of the skeletal framework of the molecule that is bonded to three or more other skeletal atoms. Clayden simplifies this description, saying that bridged bicyclic compounds "are just what the name implies—[molecules in which]

neg: Ring expansion and ring contraction of formation (seven member and larger rings). Classifying ring expansions by the mechanism of expansion and the atom(s) added allows one to see the similarities between different expansions methods and different incorporated atoms. The broadest classification comes by the mechanism of expansion. The rings can be expanded by attack of the ring onto an outside group already appended to the ring (a migration/insertion), opening of a bicycle to a single larger ring, or coupling a ring closing with an expansion. These expansions can be further broken down by what type of atom they incorporate (a carbon or a heteroatom) into

neg: Telluropyrylium the ring of telluropyrylium is fused with other aromatic rings larger aromatic structures such as tellurochromenylium, telluroflavylium, and telluroxanthylium result. Telluropyrylium Telluropyrylium is an aromatic heterocyclic compound consisting of a six member ring with five carbon atoms, and a positively charged tellurium atom. Derivatives of telluropyrylium are important in research of infrared dyes. Formerly it was named tellurapyrylium. However this is misleading, as "tellura" indicates that tellurium substitutes for carbon atom, but actually tellurium is substituted for the oxygen atom in pyrilium. In the Hantzsch-Widman system it is called tellurinium. This is the name used by Chemical Abstracts. Replacement nomenclature

neg: Amide ring Amide ring Amide Rings are small motifs in proteins and polypeptides. They consist of 9-atom or 11-atom rings formed by two COHN hydrogen bonds between a side chain amide group and the main chain atoms of a short polypeptide. They are observed with glutamine or asparagine side chains within proteins and polypeptides. Structurally similar rings occur in the binding of purine, pyrimidine and nicotinamide bases to the main chain atoms of proteins. About 4% of asparagines and glutamines form amide rings; in databases of protein domain structures, one is present, on average, every other protein. In such rings the polypeptide

neg: Spiro compound is called the "spiro atom"; in carbocyclic spiro compounds like spiro[5.5]undecane (see image at right), the spiro-atom is a quaternary carbon, and as the -ane ending implies, these are the types of molecules to which the name "spirane" was first applied (though it is now used general of all spiro compounds). Likewise, a tetravalent neutral silicon or positively charged quaternary nitrogen atom (ammonium cation) can be the spiro center in these compounds, and many of these have been prepared and described. The 2-3 rings being joined are most often different in nature, though they, on occasion, be identical [e.g., spiro[5.5]undecane,

neg: Polysilazane with alternating silicon- ("sila") and nitrogen atoms ("aza") are designated as silazanes. Simple examples of silazanes are disilazane HSi–NH–SiH and hexamethyldisilazane (HC) Si–NH–Si(CH). If only one silicon atom is bound to the nitrogen atom, the materials are known as silylamines or aminosilanes (for example triethylsilylamine (HC)Si–NH). If three silicon atoms are bound to each nitrogen atom, the materials are called silsesquiazanes. Small ring-shaped molecules with a basic network of Si-N are named cyclosilazanes (for example cyclotrisilazane [HSi–NH] ). In contrast to this, polysilazanes are silazane polymers consisting of both large chains and rings showing a range of molecular masses. A

neg: Bridged compounds a bridge of [an atom or of atoms] is thrown across from one side of the ring to the other," examples of which are shown at left and right, and below. The presence of the bridge connecting the bridgehead atoms, which are most often two non-adjacent atoms, distinguishes bridged compounds from "fused ring compounds" that have two rings linked by two adjacent atoms, and from spiro compounds that have two rings linked by a single atom. Bridged compounds may be fully carbocyclic (all carbon) or heterocyclic (having one or more non-carbon atoms). The principal and bridging rings are almost always

neg: Aromatic hydrocarbon heteroarenes, which follow Hückel's rule (for monocyclic rings: when the number of its π electrons equals 4"n" + 2, where "n" = 0, 1, 2, 3, ...), are also called aromatic compounds. In these compounds, at least one carbon atom is replaced by one of the heteroatoms oxygen, nitrogen, or sulfur. Examples of non-benzene compounds with aromatic properties are furan, a heterocyclic compound with a five-membered ring that includes a single oxygen atom, and pyridine, a heterocyclic compound with a six-membered ring containing one nitrogen atom. Benzene, CH, is the simplest aromatic hydrocarbon, and it was the first one named

neg: 4+3 cycloaddition 4+3 cycloaddition A [4+3] Cycloaddition is a cycloaddition between a 4 atom pi-system and a 3 atom pi-system to form a seven-membered ring. Allyl or oxyallyl cations (propenylium-2-olate) are commonly used 3 atom pi-systems, while a diene (such as butadiene) plays the role of the 4 atom pi-system. It represents one of the relatively few synthetic methods available to form seven-membered rings stereoselectively in high yield. The reaction is a topic of academic research. Symmetry-allowed (4+3) cycloaddition is an attractive method for the formation of historically difficult-to-access seven-membered rings. Neutral dienes and cationic allyl systems (most commonly oxyallyl cations) may

neg: Amide ring (when the tyrosine is phosphorylated); in such structures a 9-atom amide ring occurs between the amide side chain of the pentapeptide's asparagine and the main chain atoms of residue 109 of GRB2. Amide ring Amide Rings are small motifs in proteins and polypeptides. They consist of 9-atom or 11-atom rings formed by two COHN hydrogen bonds between a side chain amide group and the main chain atoms of a short polypeptide. They are observed with glutamine or asparagine side chains within proteins and polypeptides. Structurally similar rings occur in the binding of purine, pyrimidine and nicotinamide bases to the main

neg: Spiro compound carbon atoms. Cases include the presence of a spiro heteroatom such silicon and nitrogen (but also other Group IVA [14] and other atom types) connecting the rings that have been observed or are under theoretical study; moreover, there are also many cases where one or more heteroatoms appear in one or more of the rings that are joined at a carbon spiro atom (e.g., where 1 oxygen spironolactones and 2 oxygen/2 sulfur ketals/thioketals are very common). A common case is the presence of two atoms that are not carbon in one of the rings, with those two rings both attached

neg: Bioisostere a simple atom-for-atom switch. For example, a chlorine -Cl group may often be replaced by a trifluoromethyl -CF group, or by a cyano -C≡N group, but depending on the particular molecule used the substitution may result in little change in activity, or either increase or decrease affinity or efficacy depending on what factors are important for ligand binding to the target protein. Another example is aromatic rings, a phenyl -CH ring can often be replaced by a different aromatic ring such as thiophene or naphthalene which may improve efficacy, change specificity of binding, or reduce metabolically labile sites on the

neg: Organic chemistry they are prevalent in a wide range of biochemical compounds such as alkaloids, vitamins, steroids, and nucleic acids (e.g. DNA, RNA). Rings can fuse with other rings on an edge to give polycyclic compounds. The purine nucleoside bases are notable polycyclic aromatic heterocycles. Rings can also fuse on a "corner" such that one atom (almost always carbon) has two bonds going to one ring and two to another. Such compounds are termed spiro and are important in a number of natural products. One important property of carbon is that it readily forms chains, or networks, that are linked by carbon-carbon

neg: Metallocene is denoted as "η", pronounced "pentahapto". There are exceptions, such as uranocene, which has two cyclooctatetraene rings sandwiching a uranium atom. In metallocene names, the prefix before the "-ocene" ending indicates what metallic element is between the Cp groups. For example, in ferrocene, iron(II), ferrous iron is present. In contrast to the more strict definition proposed by IUPAC, which requires a d-block metal and a sandwich structure, the term metallocene and thus the denotation "-ocene", is applied in the chemical literature also to non-transition metal compounds, such as barocene (CpBa), or structures where the aromatic rings are not parallel, such

neg: Boronic acid this method is the use of diboronic acid or tetrahydroxydiboron ([B(OH)]). Boronic esters are esters formed between a boronic acid and an alcohol. The compounds can be obtained from borate esters by condensation with alcohols and diols. Phenylboronic acid can be selfcondensed to the cyclic trimer called triphenyl anhydride or triphenylboroxin. Compounds with 5-membered cyclic structures containing the C–O–B–O–C linkage are called dioxaborolanes and those with 6-membered rings dioxaborinanes. Boronic acids are used in organic chemistry in the Suzuki reaction. In this reaction the boron atom exchanges its aryl group with an alkoxy group from palladium. ][\text{Base}] R1-R2}\\ In the

neg: Chelation for the caliperlike groups which function as two associating units and fasten to the central atom so as to produce heterocyclic rings." Chelation Chelation (, ) is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central atom. These ligands are called chelants, chelators, chelating agents, or sequestering agents. They are usually organic compounds. Chelation is useful in applications such as providing nutritional supplements, in chelation therapy to remove toxic metals from the body, as contrast

neg: Heterocyclic compound reactive intermediates.<br> Common 3-membered heterocycles with "one" heteroatom are: Those with "two" heteroatoms include: Compounds with one heteroatom: Compounds with two heteroatoms: With heterocycles containing five atoms, the unsaturated compounds are frequently more stable because of aromaticity. The 5-membered ring compounds containing "two" heteroatoms, at least one of which is nitrogen, are collectively called the azoles. Thiazoles and isothiazoles contain a sulfur and a nitrogen atom in the ring. Dithiolanes have two sulfur atoms. A large group of 5-membered ring compounds with "three" heteroatoms also exists. One example is dithiazoles that contain two sulfur and a nitrogen atom. Six-membered rings

neg: Spiro compound number of atoms in the larger ring, separated by a period, in each case excluding the spiroatom (the atom by which the two rings are bonded) itself. For example, compound A is called "1-bromo-3-chlorospiro[4.5]decan-7-ol", and compound B is called "1-bromo-3-chlorospiro[3.6]decan-7-ol".The numbering will start withban atom of the smaller ring adjacent to the spiro junction i.e. the common carbon and to reach the junction and then entering to the bigger ring from the same direction. Spiranes can be chiral, in three distinct ways. First, while nevertheless appearing to be twisted, they yet may have a chiral center making them analogous to

neg: Methylphosphinic acid 940 mg/kg. Methylphosphinic acid Methylphosphinic acid is a monobasic acid, the simplest of the phosphinic acids. A central phosphorus atom is connected to a hydroxy group, a hydrogen atom, a methyl group and an oxygen. Derivatives of methylphosphinic acid can have the phosphorus connected hydrogen atom replaced by other organic groups. In early days what is now called methylphosphonic acid was also called methylphosphinic acid. Hydrolysis of methyldichlorophosphine yields methylphosphinic acid. Esters can be produced by reacting with an alcohol instead of water. Methylphosphinic acid is produced when some binary chemical agent precursors are neutralized. Rat oral value for methylphosphinic

neg: Methylphosphinic acid Methylphosphinic acid Methylphosphinic acid is a monobasic acid, the simplest of the phosphinic acids. A central phosphorus atom is connected to a hydroxy group, a hydrogen atom, a methyl group and an oxygen. Derivatives of methylphosphinic acid can have the phosphorus connected hydrogen atom replaced by other organic groups. In early days what is now called methylphosphonic acid was also called methylphosphinic acid. Hydrolysis of methyldichlorophosphine yields methylphosphinic acid. Esters can be produced by reacting with an alcohol instead of water. Methylphosphinic acid is produced when some binary chemical agent precursors are neutralized. Rat oral value for methylphosphinic acid is

neg: Ethylenetetracarboxylic dianhydride was also obtained in 2009 by Taherpour, by microwave pyrolysis of solid Meldrum's acid. Two molecules of the acid are believed to dimerize via an alkene linkage. The meldrum's-acid rings open via hydrolysis to form ethylenetetracarboxylic acid, and then the carboxylic acid units recyclize with different partners to form the dianhydride. Ethylenetetracarboxylic dianhydride Ethylenetetracarboxylic dianhydride is a chemical compound with formula , that can be seen as the twofold anhydride of ethylenetetracarboxylic acid . Its molecular backbone consists of two five-atom maleic anhydride rings, each containing one oxygen atom and four carbon atoms, sharing a pair of carbons. It is

neg: Tetradentate ligand negative charge when it is in a complex with the central atom. This may develop through the loss of hydrogen ions when the substance is dissolved. Other characteristics are the size of the rings formed by the central metal with two donor atoms and the intervening chain if the ligand. Usually these rings have five or six members, but sometimes seven atoms. For ring shaped ligands, the total number of atoms in the ring is important, as it is a determiner of the hole size for the central atom. Each additional atom in the ring enlarges the hole radius from

neg: Anomeric effect in the figure above. This prediction is supported by experimental evidence. Furthermore, this preference for the gauche position is still seen in the equatorial conformation. This term refers to the apparent preference of positively charged nitrogen substituents for the equatorial conformation beyond what normal steric interactions would predict in rings containing an electronegative atom, such as oxygen. Substituents containing carbons with partial positive charges are not seen to exhibit the same effect. Theoretical explanations for the reverse anomeric effect include an electrostatic explanation and the delocalization of the sp electrons of the anomeric carbon and oxygen lone pair. There is

neg: Thiolactone thiolactone functional group is also present in some pharmaceutical drugs such as citiolone and erdosteine. Thiolactone rings can also be found in peptides synthesized by bacteria such as "Staphylococcus aureus" in order to regulate their quorum-sensing system. Thiolactone Thiolactones are a class of heterocyclic compounds in organic chemistry. They are analogs of the more common lactones in which an oxygen atom is replaced with a sulfur atom. The sulfur atom is within the ring system and adjacent to a carbonyl group. Thiolactones can be prepared by dehydration of thiol-containing carboxylic acids. Thiolactones can be hydrolyzed back to the thiol acids

neg: 2,2'-Bis(2-indenyl) biphenyl 2,2'-Bis(2-indenyl) biphenyl 2,2'-Bis(2-indenyl) biphenyl is a ligand used to make organometallic complexes involving two aromatic-stabilized cyclopentadienyl-type carbocycle-to-metal atom bonds, complexes with distinct shapes and catalytic properties. The symmetry of the molecule--apparent in corresponding "top" and "bottom" halves of the molecule, connected together by a carbon-carbon bond between the two benzene rings (phenyl rings, see picture)--allows the two five-membered rings to participate in bonding on opposite sides of a metal atom, creating a type of sandwich compound. A prerequisite for the bonding is deprotonation of the cyclopentadiene-type five-membered ring to form the two anionic carbocycles that bind to the metal atom.

neg: Electrophilic substitution Electrophilic substitution Electrophilic substitution reactions are chemical reactions in which an electrophile displaces a functional group in a compound, which is typically, but not always, a hydrogen atom. Electrophilic aromatic substitution reactions are characteristic of aromatic compounds, and are important ways of introducing functional groups of benzene rings. The other main type of electrophilic substitution reaction is an electrophilic aliphatic substitution reaction. In electrophilic substitution in aromatic compounds, an atom appended to the aromatic ring, usually hydrogen, is replaced by an electrophile. The most important reactions of this type that take place are aromatic nitration, aromatic halogenation, aromatic sulfonation and

neg: Electrophilic substitution has a single transition state in which the old bond and the newly formed bond are both present. Electrophilic aliphatic substitution reactions are: Electrophilic substitution Electrophilic substitution reactions are chemical reactions in which an electrophile displaces a functional group in a compound, which is typically, but not always, a hydrogen atom. Electrophilic aromatic substitution reactions are characteristic of aromatic compounds, and are important ways of introducing functional groups of benzene rings. The other main type of electrophilic substitution reaction is an electrophilic aliphatic substitution reaction. In electrophilic substitution in aromatic compounds, an atom appended to the aromatic ring, usually hydrogen,

neg: Helicene conformational analysis, chirality sensing, chemical sensors and hetero-atom substitution Helicene In organic chemistry, helicenes are ortho-condensed polycyclic aromatic compounds in which benzene rings or other aromatics are angularly annulated to give helically-shaped chiral molecules. The chemistry of helicenes has attracted continuing attention because of their unique structural, spectral, and optical features. The systematic naming for this class of compounds is based on the number of rings: ["n"]helicene is the structure consisting of "n" rings. According to IUPAC, only structures as small as "n"=5 are considered helicenes. Some specific compounds also have alternate or trivial names. As the number of rings

neg: Scintillation (physics) π-orbitals interact. This occurs when their nodal planes are coplanar. In certain organic molecules π-orbitals interact to produce a common nodal plane. These form delocalized π-electrons that can be excited by radiation. The de-excitation of the delocalized π-electrons results in luminescence. The excited states of π-electron systems can be explained by the perimeter free-electron model (Platt 1949). This model is used for describing polycyclic hydrocarbons consisting of condensed systems of benzenoid rings in which no C atom belongs to more than two rings and every C atom is on the periphery. The ring can be approximated as a circle with

neg: 4+3 cycloaddition more effective than their non-fluorinated analogues, and alkoxide or amine bases work better than others. 4+3 cycloaddition A [4+3] Cycloaddition is a cycloaddition between a 4 atom pi-system and a 3 atom pi-system to form a seven-membered ring. Allyl or oxyallyl cations (propenylium-2-olate) are commonly used 3 atom pi-systems, while a diene (such as butadiene) plays the role of the 4 atom pi-system. It represents one of the relatively few synthetic methods available to form seven-membered rings stereoselectively in high yield. The reaction is a topic of academic research. Symmetry-allowed (4+3) cycloaddition is an attractive method for the formation of

neg: Fullerene a spontaneous symmetry break, yielding a puckered cage with rare T symmetry (symmetry of a volleyball). The number of six-member rings in this molecule is 20 and number of five-member rings is 12. There is an additional atom in the center of each six-member ring, bonded to each atom surrounding it. By employing a systematic global search algorithm, later it was found that the previously proposed B80 fullerene is not global minimum for 80 atom boron clusters and hence can not be found in nature. In the same paper by Sandip De et al., it was concluded that boron's energy

neg: Atom (Ray Palmer) Palmer meets Damage, son of Al Pratt, the first hero to be called Atom. The two heroes briefly acquainted during the battle, and begin to develop a friendship. Palmer stopped the Black Lantern Al Pratt from killing Damage, but was unable to keep the reanimated Jean from finishing the job. Palmer made a futile attempt to stop one of the black rings from turning Damage's corpse into an undead before Jean used his own technology to shrink him, Mera, and herself into the fully transformed Damage's ring. As Palmer and Mera battle Jean inside the black ring, Jean reveals Nekron's

neg: Alicyclic compound compounds can be predicted with Bredt's rule. Alicyclic compound An alicyclic compound is an organic compound that is both aliphatic and cyclic. They contain one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character. Alicyclic compounds may have one or more aliphatic side chains attached. The simplest alicyclic compounds are the monocyclic cycloalkanes: cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, and so on. Bicyclic alkanes include bicycloundecane, decalin, and housane.. Polycyclic alkanes include cubane, basketane, and tetrahedrane. Spiro compounds have two or more rings that are connected through only one carbon atom. The

neg: Iminosugar fibrosis. The nitrogen of the iminosugar ring structure is a hemiaminal linkage, which, like the hemiacetal of a regular glycoside, is unstable. The 1-deoxy analogs of iminosugars are C-glycosides, with the nitrogen as part of an ordinary amine linkage. Their piperidine, pyrrolidine, or similar rings are stable. Iminosugar An iminosugar, also known as an iminosaccharide, is any analog of a sugar where a nitrogen atom has replaced the oxygen atom in the ring of the structure. Iminosugars are common components of plants and may be responsible for some of their medicinal properties. The first iminosugar to be isolated from a

neg: Plant stem that function in gas exchange are called lenticels. Secondary xylem is commercially important as wood. The seasonal variation in growth from the vascular cambium is what creates yearly tree rings in temperate climates. Tree rings are the basis of dendrochronology, which dates wooden objects and associated artifacts. Dendroclimatology is the use of tree rings as a record of past climates. The aerial stem of an adult tree is called a trunk. The dead, usually darker inner wood of a large diameter trunk is termed the heartwood and is the result of tylosis. The outer, living wood is termed the sapwood.

neg: IUPAC polymer nomenclature slash, e.g., poly(but-1-ene-1,4-diyl/1-vinylethane-1,2-diyl). which are conventionally used to indicate free valences, are usually omitted from graphical representations in a polymer context. Double-strand polymers consist of uninterrupted chains of rings. In a spiro polymer, each ring has one atom in common with adjacent rings. In a ladder polymer, adjacent rings have two or more atoms in common. To identify the preferred CRU, the chain is broken so that the senior ring is retained with the maximum number of heteroatoms and the minimum number of free valences. An example is The preferred CRU is an acyclic subunit of 4 carbon atoms with

neg: Organotin chemistry the organic substituents are large, such as 2,4,6-triisopropylphenyl. Tin radicals, with the formula RSn, are called stannyl radicals. They are invoked as intermediates in certain atom-transfer reactions. For example, tributyltin hydride (tri-n-butylstannane) serves as a useful source of "hydrogen atoms" because of the stability of the tributytin radical. Organotin(II) compounds are somewhat rare. Compounds with the empirical formula SnR are somewhat fragile and exist as rings or polymers when R is not bulky. The polymers, called polystannanes, have the formula (SnR). In principle divalent tin compounds might be expected to form analogues of alkenes with a formal double bond. Indeed,

neg: Local ring to the local ring "R" is of the form formula_12 for such a "P", the conclusion is that the only rings Morita equivalent to a local ring "R" are (isomorphic to) the matrix rings over "R". Local ring In abstract algebra, more specifically ring theory, local rings are certain rings that are comparatively simple, and serve to describe what is called "local behaviour", in the sense of functions defined on varieties or manifolds, or of algebraic number fields examined at a particular place, or prime. Local algebra is the branch of commutative algebra that studies commutative local rings and their

neg: Alicyclic compound Alicyclic compound An alicyclic compound is an organic compound that is both aliphatic and cyclic. They contain one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character. Alicyclic compounds may have one or more aliphatic side chains attached. The simplest alicyclic compounds are the monocyclic cycloalkanes: cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, and so on. Bicyclic alkanes include bicycloundecane, decalin, and housane.. Polycyclic alkanes include cubane, basketane, and tetrahedrane. Spiro compounds have two or more rings that are connected through only one carbon atom. The mode of ring-closing in the formation of

neg: Polycyclic compound Polycyclic compound In the field of organic chemistry, a polycyclic compound is an organic compound featuring several closed rings of atoms, primarily carbon. These ring substructures include cycloalkanes, aromatics, and other ring types. They come in sizes of three atoms and upward, and in combinations of linkages that include tethering (such as in biaryls), fusing (edge-to-edge, such as in anthracene and steroids), links via a single atom (such as in spiro compounds), bridged compounds, and longifolene. Though poly- literally means "many", there is some latitude in determining how many rings are required to be considered polycyclic; many smaller rings are

neg: Proton nuclear magnetic resonance is attached and to electronic effects. Nuclei tend to be deshielded by groups which withdraw electron density. Deshielded nuclei resonate at higher δ values, whereas shielded nuclei resonate at lower δ values. Examples of electron withdrawing substituents are -OH, -OCOR, -OR, -NO and halogens. These cause a downfield shift of approximately 2–4 ppm for H atoms on C and of less than 1–2 ppm for H atoms on C. C is an aliphatic C atom directly bonded to the substituent in question, and C is an aliphatic C atom bonded to C. Carbonyl groups, olefinic fragments and aromatic rings contribute

neg: Sandwich compound crystallography. The correct structure had been proposed several years previously by Robert Burns Woodward and, separately, by Ernst Otto Fischer. The structure helped explain puzzles about ferrocene's conformers, the molecule features an iron atom "sandwiched" between two parallel cyclopentadienyl rings. This result further demonstrated the power of X-ray crystallography and accelerated the growth of organometallic chemistry. The best known members are the metallocenes of the formula M(CH) where M = Cr, Fe, Co, Ni, Pb, Zr, Ru, Rh, Sm, Ti, V, Mo, W, Zn. These species are also called bis(cyclopentadienyl)metal complexes. Other arenes can serve as ligands as well. Sandwich

neg: Olympicene a ketone (C=O) group (naphthanthrone) has been known for decades. Molecules where the CH spacer has been replaced with oxygen and sulfur atoms have been known for some time. The sulfur compound has a C-S-C angle of 104.53° which suggests that the sulfur atom is an sp hybridized atom rather than being sp. This suggests that the sulfur atom is not part of the pi system of the molecule. Professor Sir Martyn Poliakoff of the University of Nottingham has pointed out that the Olympic rings are not in fact interlinked, and just touching, and that a better likeness could be

neg: Poison ring from a ring bezel, is called "versare alla traditora" (“traitor’s way pouring”) and still considered offensive. Rings like this have been used throughout history to carry perfume, locks of hair, devotional relics, messages and other keepsakes, so they have also been known by other names. Artists would paint tiny portraits of loved ones, to be carried in what was called a “locket ring,” which was popular during the Renaissance. By the 17th century, jewelers were creating locket rings in the shape of caskets which served as mementos for mourners. These were called “funeral rings.” Rings with compartments are also called

neg: Bridged compounds are texts and other sources covering the title subject. Bridged compounds A bridged compound is a chemical compound, generally an organic compound, but also possibly inorganic, that has two or more rings (a ring system) that contains a "bridge"—a single atom or an unbranched chain of atoms (or even just a valence bond) that connect two "bridgehead" atoms. The bridgehead atoms are defined as any atom that is not a hydrogen, and that is part of the skeletal framework of the molecule that is bonded to three or more other skeletal atoms. Clayden simplifies this description, saying that bridged bicyclic

neg: Rutherford model remaining atomic mass. It did mention the atomic model of Hantaro Nagaoka, in which the electrons are arranged in one or more rings, with the specific metaphorical structure of the stable rings of Saturn. The plum pudding model of J. J. Thomson also had rings of orbiting electrons. Jean Baptiste Perrin claimed in his Nobel lecture that he was the first one to suggest the model in his paper dated 1901. The Rutherford paper suggested that the central charge of an atom might be "proportional" to its atomic mass in hydrogen mass units u (roughly 1/2 of it, in Rutherford's

neg: Spiro compound spiro[5.5]undecane, is also a fully carbocyclic spiro compound. While the presentation of this structure makes it appear fully planar, it is not. The best-fit planes to each six-atom ring above is near to perpendicular, and the best-fit planes to rings of spiro compounds are likewise generally non-coplanar. For instance, the structure of faux bow tie spiropentadiene, shown above, makes clear that the planes that are defined by the atoms of each ring—i.e., the best-fit plane of each cyclopropene—are orthogonal (perpendicular) to one another. Spiro compounds are considered heterocyclic if the spiro atom or any atom in either ring are not

neg: Spiro compound any simple chiral compound, and second, while again appearing twisted, the specific location of substiuents, as with alkylidenecycloalkanes, may make a spiro compound display "central chirality" (rather than axial chirality resulting from the twist); third, the substiuents of the rings of the spiro compound may be such that the only reason they are chiral arises solely from the twist of their rings, e.g., in the simplest bicyclic case, where two structurally identical rings are attached via their spiro atom, resulting in a twisted presentation of the two rings. Hence, in the third case, the lack of planarity described above gives

neg: Spiro compound rings distinguishes spiro compounds from other bicyclics: from "isolated ring compounds" like biphenyl that have no connecting atoms, from "fused ring compounds" like decalin having two rings linked by two adjacent atoms, and from "bridged ring compounds" like norbornane with two rings linked by two non-adjacent atoms. Spiro compounds may be fully carbocyclic (all carbon) or heterocyclic (having one or more non-carbon atom). One common type of spiro compound encountered in educational settings is a heterocyclic one— the acetal formed by reaction of a diol with a cyclic ketone. The common atom that connects the two (or sometimes three) rings

neg: Chalcogen reactive paramagnetic molecule that is ubiquitous to aerobic organisms and has a blue color in its liquid state. Another allotrope is O, or ozone, which is three oxygen atoms bonded together in a bent formation. There is also an allotrope called tetraoxygen, or O, and six allotropes of solid oxygen including "red oxygen", which has the formula O. Sulfur has over 20 known allotropes, which is more than any other element except carbon. The most common allotropes are in the form of eight-atom rings, but other molecular allotropes that contain as few as two atoms or as many as 20

neg: Oxocarbenium rings containing oxocarbenium ions that electronegative substituents prefer the axial or pseudo-axial positions. When the electronegative atom is in the axial position, its electron density can be donated through space to the positively charged oxygen atom in the ring. This electronic interaction stabilizes the axial conformation. Hydroxyl groups, ethers and halogens are examples of substituents that exhibit this phenomenon. Stereoelectronic effects must be taken into consideration when determining the lowest energy conformation in the analysis for nucleophilic addition to an oxocarbenium ion. In organic synthesis, vinyl oxocarbenium ions (structure on right) can be utilized in a wide range of cycloaddition

neg: Hantaro Nagaoka positive charge. In 1903, Thomson had suggested that the atom was a sphere of uniform positive electrification, with electrons scattered through it like plums in a pudding, giving rise to the term plum pudding model. Nagaoka rejected Thomson's model on the grounds that opposite charges are impenetrable. In 1904, Nagaoka proposed an alternative planetary model of the atom in which a positively charged center is surrounded by a number of revolving electrons, in the manner of Saturn and its rings. Nagaoka's model made two predictions: Both predictions were successfully confirmed by Ernest Rutherford, who mentions Nagaoka's model in his 1911

neg: Spiropyran perchloric acid, with organic bases (gaseous ammonia or amines). A spiropyran is a 2H-pyran isomer that has the hydrogen atom at position two replaced by a second ring system linked to the carbon atom at position two of the pyran molecule in a spiro way. So there is a carbon atom which is common on both rings, the pyran ring and the replaced ring. The second ring, the replaced one, is usually heterocyclic but there are exceptions. When the spiropyran is in a solution with polar solvents or when it receives heating (thermochromism) or radiation (photochromism) it becomes coloured because

neg: X Window System core protocol atoms is that atoms are not associated with clients. Once created, an atom survives until the server quits or resets (this is not the default behavior of resources). Atoms are identifiers and are therefore unique. However, an atom and a resource identifier can coincide. The string associated with an atom is called the "atom name". The name of an atom cannot be changed after creation, and no two atoms can have the same name. As a result, the name of an atom is commonly used to indicate the atom: “the atom codice_48” means, more precisely, “the atom whose associated string

neg: Intel Atom while the supporting chipset formerly code-named Menlow was called Centrino Atom. At Spring Intel Developer Forum (IDF) 2008 in Shanghai, Intel officially announced that Silverthorne and Diamondville are based on the same microarchitecture. Silverthorne would be called the Atom Z5xx series and Diamondville would be called the Atom N2xx series. The more expensive lower-power Silverthorne parts was to be used in Intel mobile Internet devices (MIDs) whereas Diamondville was to be used in low-cost desktop and notebooks. Several Mini-ITX motherboard samples have also been revealed. Intel and Lenovo also jointly announced an Atom powered MID called the IdeaPad U8. In

neg: Local ring Local ring In abstract algebra, more specifically ring theory, local rings are certain rings that are comparatively simple, and serve to describe what is called "local behaviour", in the sense of functions defined on varieties or manifolds, or of algebraic number fields examined at a particular place, or prime. Local algebra is the branch of commutative algebra that studies commutative local rings and their modules. In practice, a commutative local ring often arises as the result of the localization of a ring at a prime ideal. The concept of local rings was introduced by Wolfgang Krull in 1938 under the

neg: Atrane and the size of the rings. Atrane An atrane is a tricyclic molecule with three five-membered rings. It is a heterocyclic structure similar to the propellanes. It has a transannular dative bond from a nitrogen at one bridgehead to a Lewis acidic atom such as silicon or boron at the other bridgehead. The name "atrane" was first proposed by Mikhail Grigorievich Voronkov (). Various atranes are named depending on the central element, e.g. "silatrane" (E = silicon); "boratrane" (E = boron); "phosphatrane" (E = phosphorus), etc. It is also proposed that when Y = nitrogen, the prefix "aza" be inserted

neg: Glucose C-1 may have the same or opposite handedness as the original one (thus switching between the α and β forms). Thus, though the open-chain form is barely detectable in solution, it is an essential component of the equilibrium. The open-chain form is thermodynamically unstable, and it spontaneously isomerizes to the cyclic forms. (Although the ring closure reaction could in theory create four- or three-atom rings, these would be highly strained, and are not observed in practice.) In solutions at room temperature, the four cyclic isomers interconvert over a time scale of hours, in a process called mutarotation. Starting from any

neg: Organoboron chemistry the alkene on the "most substituted" carbon atom, that is where the partially negatively charged hydrogen atom adds, leaving the "least substituted" carbon atom for the boron atom. The so-called anti-Markovnikov addition because when the boron is replaced with a hydroxyl group the overall reaction is addition of water over the double bond in what appears to be an anti-Makovnikov addition. This is most pronounced when the boron compound has very bulky substituents. One organoboron reagent that is often employed in synthesis is 9-BBN which is generated from the reaction of cyclooctadiene and diborane. Hydroborations take place stereospecifically in a

neg: Metalloprotease inhibitor rheumatoid- and osteo-arthritis, also has the marimastat succinate motif. Its clinical trial was terminated prematurely. <br>MMI-166 has an N-arylsulfonyl-α-aminocarboxylate zinc-binding group, different from the hydroxamate-zinc binding group seen in MMI-270 and Cipemastat. It also has a triaryl substitution that the other structures didn‘t have. ABT-770 and Prinomastat also have an aryl substitution. In ABT-770 the two phenyl rings are directly connected but in Prinomastat the two phenyl rings are connected by an oxygen atom, forming a diphenylether. These three permutations direct the SAR away from MMP-1 and toward the „deep pocket“ MMPs such as the gelatinases. ABT-770 shows anticancer activity

neg: Iminodiacetic acid Iminodiacetic acid Iminodiacetic acid, HN(CHCOH), often abbreviated to IDA, is a dicarboxylic acid amine (the nitrogen atom forms a secondary amino group, not an imino group as the name suggests). The iminodiacetate anion can act as a tridentate ligand to form a metal complex with two, fused, five membered chelate rings. The proton on the nitrogen atom can be replaced by a carbon atom of a polymer to create an ion-exchange resin, such as chelex 100. IDA forms stronger complexes than the bidentate ligand glycine and weaker complexes than the tetradentate ligand nitrilotriacetic acid. It can also act as a

neg: Rings of Saturn produced when ultraviolet light from the Sun interacts with water ice in the rings. Chemical reactions between water molecule fragments and further ultraviolet stimulation create and eject, among other things, O. According to models of this atmosphere, H is also present. The O and H atmospheres are so sparse that if the entire atmosphere were somehow condensed onto the rings, it would be about one atom thick. The rings also have a similarly sparse OH (hydroxide) atmosphere. Like the O, this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic

neg: Exotic atom includes strange particles called hyperons. Such hypernuclear atoms are generally studied for their nuclear behaviour, falling into the realm of nuclear physics rather than atomic physics. In condensed matter systems, specifically in some semiconductors, there are states called excitons which are bound states of an electron and an electron hole. Exotic atom An exotic atom is an otherwise normal atom in which one or more sub-atomic particles have been replaced by other particles of the same charge. For example, electrons may be replaced by other negatively charged particles such as muons (muonic atoms) or pions (pionic atoms). Because these substitute

neg: Bicyclic molecule Bicyclic molecules have a strict nomenclature. The root of the compound name depends on the total number of atoms in all rings together, possibly followed by a suffix denoting the functional group with the highest priority. Numbering of the carbon chain always begins at one bridgehead atom (where the rings meet) and follows the carbon chain along the longest path, to the next bridgehead atom. Then numbering is continued along the second longest path and so on. Fused and bridged bicyclic compounds get the prefix "bicyclo", whereas spirocyclic compounds get the prefix "spiro". In between the prefix and the suffix,

neg: Borate anions. The condensation reaction for the formation of tetraborate(2-) is as follows: The tetraborate anion (tetramer) includes two tetrahedral and two trigonal boron atoms symmetrically assembled in a fused bicyclic structure. The two tetrahedral boron atoms are linked together by a common oxygen atom and each also bears a negative net charge brought by the supplementary OH groups laterally attached to them. This intricate molecular anion also exhibits three rings: two fused distorted hexagonal (boroxole) rings and one distorted octagonal ring. Each ring is made of a succession of alternate boron and oxygen atoms. Boroxole rings are a very common

neg: Photofragment-ion imaging to the recoil velocity between the two fragments. Of course, the more energy that is used to excite the O vibrations, the less will be available for the recoil. REMPI of the O(D) atom in conjunction with the product imaging technique provides an image that can be used to determine the O(D) three-dimensional velocity distribution. A slice through this cylindrically symmetric distribution is shown in the figure, where an O(D) atom that has zero velocity in the center-of-mass frame would arrive at the center of the figure. Note that there are four rings, corresponding to four main groups of O(D)

neg: Allene it is possible to reduce just one of the double bonds of an allene. Many rings or ring systems are known by semisystematic names that assume a maximum number of noncumulative bonds. To unambiguously specify derivatives that include cumulated bonds (and hence fewer hydrogens than would be expected from the skeleton), a lowercase delta may be used with a subscript indicating the number of cumulated double bonds from that atom, e.g. 8δ-Benzocyclononene. This may be combined with the λ-convention for specifying nonstandard valency states, e.g. 2λδ,5λδ-Thieno[3,4-c]thiophene. Allene An allene is a compound in which one carbon atom has double bonds

neg: Blackest Night to outrace their rings. Allen time-travels himself and Jordan two seconds into the future and disables their rings. Mera and the Atom arrive. John Stewart warns Hal that every Black Lantern in the universe is heading for Earth. Jordan says they need the entire seven Corps to unite to produce White Light. While they summon the seven Corps to Earth, Ganthet duplicates the seven colored rings present and deputizes non-Corps members Ganthet as Green, Barry Allen as Blue, Mera as Red, Lex Luthor as Orange, Scarecrow as Yellow, Atom as Indigo, and Wonder Woman as Violet after separating her from

neg: A Is for Atom tighter editing, new music and a focus on nuclear power as opposed to nuclear bombs. A narrator is relating what is an atom and how atomic energy can be harnessed by man to produce "limitless" energy. Dr. Atom (a caricature with an atom for a head) then explains the similarities between the solar system and atomic structure. He then goes on to relate how the atom is made up of protons, neutrons, and electrons. After this, the narrator explains how there are more than 90 elements with many possible isotopes for each. The history of atomic energy is then overviewed

neg: Degree of unsaturation spectroscopy, as well as qualitative inspection. It is based on comparing the actual molecular formula to what would be a possible formula if the structure were saturated—having no rings and containing only σ bonds—with all atoms having their standard valence. The formula for degree of unsaturation is: where "n" is the number of atoms with valence "v". That is, an atom that has a valence of "x" contributes a total of "x" − 2 to the degree of unsaturation. The result is then halved and increased by 1. For certain classes of molecules, the general formula can be simplified or

neg: Expanding Monomers contains at least one non-carbon atom and that the rings are opening in asymmetrical manner (meaning for example that one oxygen forms an carbonyl group and one an ether group). Compound classes which are fulfilling these requirements are spiro orthoesters, spiro orthocarbonates, bicyclic ketal lactones and bicyclic orthoesters. Most expanding monomers are orthoesters, either spiro orthoesters, bicyclic orthoesters or orthocarbonates. Some expanding monomers are lactones. These classes are listed in the following table. There are three possibilities given in the literature for the synthesis of expanding monomers which are based on orthoesters. The first possibility is the reaction of an

neg: Sesquifulvalene on the carbon atom of heptagonal ring and a partial positive charge on the carbon atom of pentagonal ring due to Baird's rule. Sesquifulvalene Sesquifulvalene or Pentaheptafulvalene is a hydrocarbon in the fulvalene class with chemical formula CH. It is composed of linked cyclopentadiene and cycloheptatriene rings. In the ground state, which is a singlet state, the central double bond is polarized, with a partial positive charge on the carbon atom of heptagonal ring and a partial negative charge on the carbon atom of pentagonal ring. This shift makes each ring have closer to 4"n"+2 π electrons, in keeping with

neg: Atomic formula contains the atoms When all of the terms in an atom are ground terms, then the atom is called a ground atom or "ground predicate". Atomic formula In mathematical logic, an atomic formula (also known simply as an atom) is a formula with no deeper propositional structure, that is, a formula that contains no logical connectives or equivalently a formula that has no strict subformulas. Atoms are thus the simplest well-formed formulas of the logic. Compound formulas are formed by combining the atomic formulas using the logical connectives. The precise form of atomic formulas depends on the logic under consideration;

neg: Norsteroid Norsteroid "Norsteroids" (nor-, L. "norma", from "normal" in chemistry, indicating carbon removal) are a structural class of steroids that have had an atom or atoms (typically carbon) removed, biosynthetically or synthetically, from positions of branching off of rings or side chains (e.g., removal of methyl groups), or from within rings of the steroid ring system. For instance, 19-norsteroids (e.g., 19-norprogesterone) constitute an important class of natural and synthetic steroids derived by removal of the methyl group of the natural product progesterone; the equivalent change between testosterone and 19-nortestosterone (nandrolone) is illustrated below. Norsteroid examples include: 19-norpregnane (from pregnane), desogestrel, ethylestrenol,

neg: Norsteroid etynodiol diacetate, ethinylestradiol, gestrinone, levonorgestrel, norethisterone (norethindrone), norgestrel, norpregnatriene (from pregnatriene), quinestrol, 19-norprogesterone (from a progesterone), Nomegestrol acetate, 19-nortestosterone (from a testosterone), and norethisterone acetate. Norsteroid "Norsteroids" (nor-, L. "norma", from "normal" in chemistry, indicating carbon removal) are a structural class of steroids that have had an atom or atoms (typically carbon) removed, biosynthetically or synthetically, from positions of branching off of rings or side chains (e.g., removal of methyl groups), or from within rings of the steroid ring system. For instance, 19-norsteroids (e.g., 19-norprogesterone) constitute an important class of natural and synthetic steroids derived by removal of the methyl

neg: Hydrogen bond type of bonding is called "bifurcated" (split in two or "two-forked"). It can exist, for instance, in complex natural or synthetic organic molecules. It has been suggested that a bifurcated hydrogen atom is an essential step in water reorientation. Acceptor-type hydrogen bonds (terminating on an oxygen's lone pairs) are more likely to form bifurcation (it is called overcoordinated oxygen, OCO) than are donor-type hydrogen bonds, beginning on the same oxygen's hydrogens. For example, hydrogen fluoride—which has three lone pairs on the F atom but only one H atom—can form only two bonds; (ammonia has the opposite problem: three hydrogen atoms

neg: Uranocene reactive toward oxygen, being pyrophoric in air but stable to hydrolysis. Considering the molecule to be U(CH), the η-cyclooctatetraenide groups are planar, as expected for a ring containing 10 π-electrons, and are mutually parallel, forming a sandwich containing the uranium atom. In the solid state, the rings are eclipsed, conferring "D" symmetry on the molecule. In solution the rings rotate with a low energy barrier. The uranium-cyclooctatetraenyl bonding was shown by photoelectron spectroscopy to be primarily due to mixing of uranium 6d orbitals into ligand pi orbitals and therefore donation of electronic charge to the uranium, with a smaller such

neg: Tetrapyrrole Tetrapyrrole Tetrapyrroles are a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by (=- or -- units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four carbon and one nitrogen atoms. Tetrapyrroles are common cofactors in biochemistry and their biosynthesis and degradation feature prominently in the chemistry of life. Some tetrapyrroles are the active cores of some compounds with crucial biochemical roles in living systems, such as hemoglobin and chlorophyll. In these two molecules, in particular, the pyrrole macrocycle ring frames a metal atom, that forms

neg: Neck ring allowed to wear the rings, called "dzilla". Metal rings are also worn on different parts of the body, not just the neck. Traditionally these rings are given to a wife by her husband, and not removed until the husband's death; however, these rings are individual and do not function as a body modification. The rings are usually made of copper or brass. Neck ring Neck rings, or neck-rings, are any form of stiff jewellery worn as an ornament around the neck of an individual, as opposed to a loose necklace. Many cultures and periods have made neck rings, with both

neg: Exotic atom Exotic atom An exotic atom is an otherwise normal atom in which one or more sub-atomic particles have been replaced by other particles of the same charge. For example, electrons may be replaced by other negatively charged particles such as muons (muonic atoms) or pions (pionic atoms). Because these substitute particles are usually unstable, exotic atoms typically have very short lifetimes. In a "muonic atom" (previously called a "mu-mesic" atom, now known to be a misnomer as muons are not mesons), an electron is replaced by a muon, which, like the electron, is a lepton. Since leptons are only sensitive

neg: Fenestrane 155 pm, in this fenestrane, the bonds extending from the central carbon atom are shortened to 149 pm while those at the perimeter are lengthened to 159 pm. A diterpene called laurenene containing a [5.5.5.7]fenestrane ring system was the first natural fenestrane to be discovered. The first fenestrane ever synthesized was a [4.5.5.6]fenestrane: Pyramidane ([3.3.3.3]fenestrane) is the smallest possible fenestrane, and has never been synthesised. If the central carbon were to be tetrahedral, it would have the form of spiropentadiene, but with additional bonds between the two cyclopropyl rings rather than double-bonds within them. The analogous germa- and stannapyramidanes, with

neg: Balanol interactions between balanol and the residues of the catalytic cleft of PKA; for example, two water molecules form a bridge to allow balanol’s N1’ atom to interact with the hydroxyl group of Tyr330. However, the tight interaction of balanol with the ATP-binding site that leads to balanol’s potency as an inhibitor is not due to hydrogen bonding but rather because of the predominant nonpolar interactions the molecule makes. For instance, balanol’s benzophenone rings are positioned beside the glycine-rich loop and further from the more polar catalytic loop. Compared to ATP’s triphosphates, accommodating balanol’s benzophenone rings induces the rearrangement of catalytic

neg: Sulfur over 30 solid allotropes, more than any other element. Besides S, several other rings are known. Removing one atom from the crown gives S, which is more of a deep yellow than the S. HPLC analysis of "elemental sulfur" reveals an equilibrium mixture of mainly S, but with S and small amounts of S. Larger rings have been prepared, including S and S. Amorphous or "plastic" sulfur is produced by rapid cooling of molten sulfur—for example, by pouring it into cold water. X-ray crystallography studies show that the amorphous form may have a helical structure with eight atoms per turn.

neg: Germanate interconnected by channels defined by 30-membered rings (the naturally occurring zeolite faujasite with channels defined by 12-membered rings). Zeolites with frameworks containing silicon and germanium (silicogermanates), aluminium and germanium (aluminogermanates) and zirconium and germanium (zirconogermanates) are all known. Germanate In chemistry germanate is a compound containing an oxyanion of germanium. In the naming of inorganic compounds it is a suffix that indicates a polyatomic anion with a central germanium atom, for example potassium hexafluorogermanate, KGeF. Germanium is similar to silicon forming many compounds with tetrahedral {GeO} units although it can also exhibit 5 and 6 coordination. Analogues of all the

neg: Atom (Ray Palmer) tiny aliens were murdered in hopes Ray would return as the Atom and become a tool for the Cabal (as Ray worked for the CIA in his earlier years). Instead, Palmer shrank the five agents to six-inch height and the CIA would employ them as a group called Micro/Squad. The Atom would take on new enemies during this period, such as Humbug, a sentient robot in control of an army of duplicates of itself, and Strobe, a technological armor-clad crook. Micro/Squad would also return, attempting to murder Palmer for what he did to them. Instead, teammate Ginsburg dies in the

neg: Atom laser exploited. Atom laser An atom laser is a coherent state of propagating atoms. They are created out of a Bose–Einstein condensate of atoms that are output coupled using various techniques. Much like an optical laser, an atom laser is a coherent beam that behaves like a wave. There has been some argument that the term "atom laser" is misleading. Indeed, "laser" stands for "Light Amplification by Stimulated Emission of Radiation" which is not particularly related to the physical object called an atom laser, and perhaps describes more accurately the Bose–Einstein condensate (BEC). The terminology most widely used in the community

neg: Atom laser Atom laser An atom laser is a coherent state of propagating atoms. They are created out of a Bose–Einstein condensate of atoms that are output coupled using various techniques. Much like an optical laser, an atom laser is a coherent beam that behaves like a wave. There has been some argument that the term "atom laser" is misleading. Indeed, "laser" stands for "Light Amplification by Stimulated Emission of Radiation" which is not particularly related to the physical object called an atom laser, and perhaps describes more accurately the Bose–Einstein condensate (BEC). The terminology most widely used in the community today

neg: Aromaticity of the ring, and each of these p-orbitals contains one π-electron. Additionally, the nitrogen atom is also sp-hybridized and has one electron in a p-orbital, which adds up to 6 p-electrons, thus making pyridine aromatic. The lone pair on the nitrogen is not part of the aromatic π system. Pyrrole and imidazole are both five membered aromatic rings that contain heteroatoms. In pyrrole, each of the four sp-hybridized carbons contributes one π-electron, and the nitrogen atom is also sp-hybridized and contributes two π-electrons from its lone pair, which occupies a p-orbital. In imidazole, both nitrogens are sp-hybridized; the one in

neg: Nest (protein structural motif) are liable to be hydrogen bonded to a negatively charged, or partially negatively charged, atom, often an oxygen atom. The NH of the second residue may also be hydrogen bonded to the same atom but usually points somewhat away. These main chain atoms form a concavity called a nest into which an anionic atom fits. Such anionic atoms are sometimes called eggs and more than one egg may occur bound to a nest. The oxyanion hole of the intestinal serine proteases is a functional example of a nest. Another occurs at the bottom of a deep cavity in the antibiotic