notes on nomenclature 101, [[011, [~10111,l~iI01111,etc. The 1971 IUPAC Rules for Inorganic Nomenclature recommends that a space be left between the outer square brackets and the remainder of the formula.
Un;rerr;ly of South Florid.
Tompa 3 3 6 2 0
KURT LOENING ROY M. ADAMS
Chemicd Abstrods Service Columbus, Ohio 4 3 2 1 0
Parentheses are used for indicating the other atom involved vhen a double bond is directed to an atom other than that bearing the next highest locant
Geneva College Bearer Follr, Penntylvonio 1 5 0 1 0
Use of Enclosing Marks and Letters How are Enclosing Marks Used?
Enclosing marks are used in formulas to enclose sets of identical groups of atoms CadPod~
BIN(CH&I,
In names, enclosing marks generally are used following bis, tris, etc. around all complex expressions, and elsewhere to avoid any possibility of ambiguity (see previous Notes). As with the case of multiplicative affixes, there are txro attitudes toward the use of enclosing marks. Some use them only when absolutely necessary, while others use them every time a multiplicative affixis used. For example, the former omit enclosing marks in such cases as trisdecyl, tetraltishydroxymethyl, and tridecyl. The use of one set of enclosing marks within another necessitates an order of precedence or nesting order. The normal order is braces supe~ior to brackets and brackets to parentheses or ([()I).' Note, however, that Chemical Abstracts does not use braces (curly brackets) and thereby saves two characters in machine type~etting.~Further, since Werner introduced the oustom in the formulas of coordination compounds, brackets have been reserved to enclose a complex ion or a neutral coordination entity. Hence enclosing marks should be nested with brackets, as follows
In organic names, brackets also have some specific uses. They are used to enclose the locants u.hich define the manner of fusion of the components in names for fused polycyclic hydrocarbons
This same practice is extended t o fused heterocyclic systems. For some bridged systems, brackets are used to enclose the designation of the number of carbon atoms in each bridge CH,-CH-CH,-CH,
I
CH,
bicycl$5.2.0]nonane
CH2-CH*,-CH, T h e Britishusea somewhat different set of names for enclosing marks (
1
)
'l
Ameriean parentheses brackets braces
British curved brackets square brackets curly brackets
The use braces was abandoned in C . A . indexes a i t h the b e ginning in the 7th Collective period, Vol. 56, 1962.
For some spiro systems the designation of the number of atoms linked to the spiro atom is enclosed in brackets. Volume
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Other examples of uses of italicized symbols of the elements in organic namm are CNO
I
0
benzonitrile, N-oxide
How ore Letters Used in Nomencloture?
Capital Letters The symbols of the elements, printed in italics are used to designate (a) The element in a heteroatomic chain or ring a t which there is substitution
(b) The element in a ligand which is coordinated to a central atom
N-ethyl-P,P,P-triphenylphosphineimide
Primed Capital Letters The practices under (a) and (h) in the above section require primed letters when two or more atoms of the same element are involved in the same or similar situations
Lower Case Letters The most familiar use of italicized lower case letters is as abbreviations for certain structural prefmes
(c) The presence of bonds between two metal atoms (oc),F~(c.H~s)~F~(co~) bis-(pethy1thio)-bis(tricarbonyliron)(Fe-Fe)
(d) The point of attachment in some addition compounds (e) A specific isotope in isotopically labeled compounds
o-, m-, and p for orlho-, meta, and para-; n- fqr normal-; asand s-for asymetrioal and syrnetrical; d- and C for deuteriumand tritium; d-and I- far deztro- (dextrarotary)and leuo- (levorotory); and cis-, trans-, anti- and syn- for definite structural relationships. Less common is u- for vieinal. Carbohydate nomenclature has several prefixes such as erylhro- and gluco-.
For distinguishing isomers among fused polycyclic hydrocarbons and fused heterocyclic systems, it is necessary to designate where the fusion is regarded as having taken place. This is dOne by designating the peripheral sides of the base component a, b, c, etc. The letters are enclosed in brackets.
16NH3 ammonia (I6N)
If) The position of hydrogen in some polycyclic hydrocarbons and fused heterocyclics in order to distinguish among possible isomers
( g ) The position of hydrogenin a nearly perfluorinated hydrocarbon CHFaCACFCHFCF8 1H,4H-decafluoropentane
Roman D and L are used for configurational relationships and R and S for absolute configurations. Roman E and Z are used for specifying configurations about double bonds. Italicized symbols of the elements are sometimes used to indicate unusual valence.
254
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Journol of Chemical E+cotion
For fused polycyclic hydrocarbons and heterocycles, locants are assigned only to the peripheral ring atoms and not to the bridgehead atoms. When it is necessary to refer to these bridgehead atoms they are given the number of the preceediug atoms followed by an a, b, etc.
CJI,CH,AsO(OC6H,),
Loner case letters printed in italics are used as locants for the spatial positions around the central atom in a coordination compound
4
d
locants for a n octahedral configuration
diphenyl a-tolueneareonate
and to indicate the distance between two functional groups, as in p-diketones and y-lactones. The letters a! and p are used for stereodescriptors. Omega, w, is used to indicate the last or end position rather than the 24th (order in alphabet). Greek letters are no longer used to designate positions in a heterocyclic ring. Several Greek letters have special meaning
1
This usage is extended to all configurations, to multinuclear coordination compounds and to atomicclu~ters.~ In thc United Kingdom but not so commonly in this country, letters are used as supcrscripts. Thus i, n, s, and t are used with abbrcviations for organic radicals to indicate iso-, normal-, secondary-, and tertiary But = tert-butyl
Greek Letters
Chemical nomenclature makes use of Greek letters in a number of ways. Allotropic and polymorphic forms are commonly distinguished by the use of Greek letters: A-sulfur, ry- and &quartz, as are alloy phases: p-brass. Greek letters arc used to indicate positions on side chains in some aromatic derivatives
A formerly used t o indicate a double bond 6 and A (also A t ~ n d A ) sreused t o indicate chiralitv. q (for hapto) indicates bonding of unsaturated organic groups
to a metal with no theoretical implications as to the nature of the bondine. pis used to designate a bridging group in coordination compounds. r is used in the expression r-bond to indicate a specific kind of linkage; the symbol has been carried into specific names such as bis(r-benzene)ehromium(O) for Cr(CaHa)2. The symbol q is preferred because it carries no theoretical implication es to the type of bonding.4.'
See subsequent discussions on the nomenclature of coordination compounds and boron hydride. 'COTTON,F. A,, J. Amw. Chem. Soc., 90, 6230 (1968). The older organic literature used r as a locant on the camphor molecule. However, d-a-bromo camphor-n-sulfonate is better referred to as d-3-bromo-8-campho~~dfonate.
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