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1. Pyrimidine-2,4,6(1H,3H,5H)-trione (trivial name barbituric acid) and derivatives: (keto tautomeric form)

2. Salts of barbituric acid and its derivatives.

carbonyl oxides:

1,3-Dipolar compounds having the structure R2C--O+=O [2headed arrow] R2C=O+-O-. Also called peroxo compounds. See also oxonium ylides (2).


Compounds in which a multidentate ligand, such as an enolate anion of a [beta]-diketone, is bound to a receptor center (central atom of a coordination complex).


Inclusion compounds in which the guest molecule is in a cage formed by the host molecule or by a lattice of host molecules.

fluoresceins:See xanthene dyes.

Herz compounds:

1,2[lambda]4,3-Benzodithiazolium chlorides (formed in the reaction of aniline and derivatives thereof with disulfur dichloride).


Analogues of alkenes in which a doubly bonded carbon atom is replaced by a heteroatom. E.g. H2Si=CH2 methylidenesilane (silene less preferred), MeN=CH2 N-methylmethanimine.


Cumulenes in which one or more carbon atoms of the cumulative bond system have been replaced by heteroatoms. E.g. O=C=C=C=O, but not CH2=C=O, ketene, nor O=C=O, carbon dioxide, which are heteroallenes.

hydrocarbyl groups:

Univalent groups formed by removing a hydrogen atom from a hydrocarbon. Cf. heterocyclyl, organoheteryl, organyl groups. E.g. ethyl, phenyl.

hydrocarbylene groups:

Divalent groups formed by removing two hydrogen atoms from a hydrocarbon, the free valencies of which are not engaged in a double bond. E.g. 1,3-phenylene, -CH2CH2CH2- propane-1,3-diyl, -CH2- methylene.

hydrocarbylidene groups:

Divalent groups, R2C=, formed by removing two hydrogen atoms from the same carbon atom of a hydrocarbon, the free valencies of which are engaged in a double bond.

hydrocarbylidyne groups:

Trivalent groups, RC[triple bond], formed by removing three hydrogen atoms from the same carbon atom of a hydrocarbon, the free valencies of which are engaged in a triple bond.

inclusion compounds:

Compounds in which one kind of molecule (the guest compound) is embedded in the matrix of another (the host compound). See also clathrates, crown compounds, cryptands/cryptates and intercalation compounds. J. L. Atwood, J. E. D. Davies and D. D. MacNicol, Eds., Inclusion Compounds, Academic Press, 1984.

intercalation compounds:

Compounds resulting from reversible inclusion, without covalent bonding, of one kind of molecule in a solid matrix of another compound, which has a laminar structure. The host compound, a solid, may be macromolecular, crystalline, or amorphous. See also inclusion compounds. M. S. Whittingham and A. J. Jacobson, Eds., Intercalation Chemistry, Academic Press, 1982.

lariat ethers:

Crown ethers (see under crown compounds) having a side chain that holds one or more additional coordinating sites. G.W. Gokel, K.A. Arnold, M. Delgado, L. Echeverria, V.J. Gatto, D. A. Gustowski, J. Hernandez, A. Kaifer, S.R. Miller and L. Echegoyen, PAC 60, 461-465 (1988).

leuco bases:

Colourless compounds formed by reduction of triphenylmethane dyes. Generally, they are amino or hydroxy derivatives of triphenylmethane. Use of this class name, which is more or less parochial to the technology of dyes, is not endorsed. E.g. (p-Me2NC6H4)2CHPh the leuco base of Malachite Green.

leuco compounds:

Dihydroxy polycyclic aromatic compounds which on oxidation form polycyclic quinone dyes (intermediates in vat dyeing). Use of this class name, which is more or less parochial to the technology of dyes, is not endorsed.


A prefix meaning part, partial, or fragment, used in formation of compound words. E.g. merocyanines are compounds related to cyanines but have a nitrogen atom at only one end of the chromogenic system instead of at both ends.


Compounds having two [beta]-haloalkyl groups bound to a sulfur atom, as in (XCH2CH2)2S, and their analogues, the nitrogen (and phosphorus) mustards, (XCH2CH2)2NR. Compounds having one [beta]-haloalkyl group and one [beta]-hydroxyalkyl group on S are termed hemi- or semi-mustards by some chemists.

organoheteryl groups:

Univalent groups containing carbon, which are thus organic, but which have their free valence at an atom other than carbon. This collective term is seldom used; specific subclasses are more frequently encountered (organothio- or organylthio, organogermanium- or organylgermanium groups). The synonymous term organoelement groups is occasionally encountered. E.g. phenoxy, acetamido, pyridinio (C5H5N+-), thiocyanato (N[triple bond]C-S-), trimethyl silyl; but not hydroxyphenyl, aminoacetyl. Cf. organyl.

organyl groups:

Any organic substituent group, regardless of functional type, having one free valence at a carbon atom. See heterocyclyl groups, hydrocarbyl, organoheteryl. E.g. CH3CH2- , ClCH2- , CH3C(=O)-, 4-pyridylmethyl. Note: organyl is also used in conjunction with other terms, as in organylthio- (e.g. MeS-) and organyloxy.

oxo compounds:

Compounds containing an oxygen atom, =O, doubly bonded to carbon or another element. The term thus embraces aldehydes, carboxylic acids, ketones, sulfonic acids, amides and esters. Oxo used as an adjective (and thus separated by a space) modifying another class of compound, as in oxo carboxylic acids, indicates the presence of an oxo substituent at any position. To indicate a double-bonded oxygen that is part of a ketonic structure, the term keto is sometimes used as a prefix, but such use has been abandoned by IUPAC for naming specific compounds. A traditional use of keto is for indicating oxidation of CHOH to C=O in a parent compound that contains OH groups, such as carbohydrates. E.g. 3-ketoglucose. Cf. ketoaldonic acids, ketoaldoses.


Oxoacids (and its variants oxyacids, oxo acids, oxy-acids, oxiacids, oxacids) is a traditional name for any acid having oxygen in the acidic group. The term stands in contradistinction to 'hydracids' (e.g. HCl) lacking oxygen.

The term oxoacid now refers to a compound which contains oxygen, at least one other element, and at least one hydrogen bound to oxygen, and which produces a conjugate base by loss of positive hydrogen ion(s) (hydrons). CNIC, Nomenclature of Inorganic Chemistry, Recommendations 1990, Blackwell Scientific Publications, Rule I-9.2. E.g. P(OH)3 , RC(=O)OH, HOSOH, HOCl, HON=O, (HO)2SO2, RP(=O)(OH)2. See also oxo carboxylic acids.


Compounds consisting wholly of carbon and oxygen. E.g. CO, O=C=O , O=C=C=C=O,

oxyacid/oxy-acid: See oxoacid.

peroxo compounds: See carbonyl oxides.

phenonium ions:

The traditional generic name for those cyclohexadienyl cations that are spiro-annulated with a cyclopropane unit. Phenonium ions constitute a subclass of arenium ions. GTPOC (bridged carbocations).


3,3-Bis(hydroxyaryl)-2-benzofuran-1(3H)-ones generally derived from the condensation of phthalic anhydride with phenols. Cf. xanthene dyes. E.g. phenolphthalein.


3,3-Di(hydrocarbyl) or 3-hydrocarbylidene-2-benzofuran-1(3H)-ones. Cf. phthaleins.


Salts or charge-transfer complexes of picric acid (2,4,6-trinitrophenol). Cf. styphnates.

pseudo acids:

Potentially acidic compounds that require some structural reorganization, such as keto-enol tautomerization, having a non-negligible activation energy, in order to show normal acidic properties. E.g. nitroalkanes:

pseudo bases:

Hydroxy compounds that give salts with acids by formation of water accompanied by a change of constitution. Cf. anhydro bases.


Compounds that resemble the halogen elements, X2, in their chemistry. E.g. (CN)2 cyanogen, (SCN)2 thiocyanogen, ICN iodine cyanide. Certain ions that have sufficient resemblance to halide ions are sometimes referred to as pseudohalide ions. E.g. N3-, SCN-, CN-.


A prefix designating compounds formed by heating a compound, usually with the elimination of water, carbon dioxide, or other simple molecule. E.g. pyroglutamic acid from glutamic acid.

Reissert compounds:

Compounds formed by formal addition of an acyl group and a cyano group to a nitrogen atom and carbon atom, respectively, of a nitrogen-carbon bond in quinolines, isoquinolines, and related nitrogen heterocycles. E.g.

rhodamine dyes:

Dyes derived from condensation of phthalic anhydride with m-dialkylaminophenols. Cf. xanthene dyes.


Salts or charge-transfer complexes of styphnic acid (2,4,6-trinitrobenzene-1,3-diol). NOC Rule C-816.5. Cf. picrates.


Mesoionic compounds having the 1,2,3-oxadiazole skeleton bearing an oxygen atom attached to the 5 position:

(These structures represent only two canonical forms.)

sydnone imines:

Imines of sydnones (i.e. having an imino group in place of the exocyclic oxygen atom).

(These structures represent only two canonical forms.)


This term has inconsistently been used to mean cyclohepta-1,3,5-trienes or to mean cyclohepta-1,3,5-trienes in dynamic equilibrium with bicyclo[4.1.0]hepta-2,4-dienes, so that the structure of the bulk substance is indeterminate in the time scale of the method of observation. Use of this term is therefore discouraged.


2-Hydroxycyclohepta-2,4,6-trienones and derivatives formed by substitution. Cf. tropones.


Compounds that contain the cyclohepta-2,4,6-trienone ring system.

tropyl radicals:

The delocalized radicals derived formally by abstraction of one hydrogen from the CH2 group of cyclohepta-1,3,5-triene and substitution derivatives thereof.

tropylium ions:

The delocalized carbenium ion, cycloheptatrienylium, C7H7+, derived formally by detachment of one hydride ion from the CH2 group of cyclohepta-1,3,5-triene and substitution derivatives thereof.


1,1'-Di(hydrocarbyl)-4,4'-bipyridinium salts.

xanthene dyes:

Dyes derived by condensation of phthalic anhydride with resorcinol (and derivatives) or m-aminophenol (and derivatives), of which fluorescein is the prototype (all such dyes have the xanthene nucleus). See also phthaleins, rhodamine dyes.


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