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Halogen, Nitro, Nitroso and Azido Compounds
In
substitutive nomenclature certain functional groups have not been assigned suffix names and must therefore always be designated by prefixes (see Chapter 8). The most frequently occurring of these groups are halogen atoms and the groups — N O , —NO, and —N3. The naming of compounds containing these substituents is discussed in this chapter, except for acid halides and acid azides (see Chapter 17) and ionic compounds of the quaternary ammonium type (see Chapter 24). 2
Recommended Nomenclature Practice Compounds containing one or more F , Cl, Br, I, NO2, N O , or N3 groups each singly bound to a non-acyl carbon atom are named substitutively by combining the appropriate prefixes (see Table 8.1) with the name of the parent chain or ring system. CH N0 3
CH
Nitromethane
3
2-Azido-2-methylpropane
3
CH C-N 3
CH
2
3
(2-Chloroethy l)benzene
CgH5CH CH Cl 2
2
NO l-Nitrosonaphthalene
GH
3
Br 211 In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
212
NOMENCLATURE OF ORGANIC COMPOUNDS
As illustrated by the last example, prefix names of functional and nonfunctional substituting groups are considered together for arrangement in alphabetical order. The presence of multiplying prefixes does not affect this order of citation (see Chapter 8). Names of several other groups containing halogen or nitrogen that are always cited as prefixes are listed in Table 8.1.
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Discussion Simple halogen and azido compounds have often been given radicofunctional names (see Chapter 9)—e.g., ethyl chloride and benzyl azide—but modern systematic nomenclature calls for the substitutive method, which is of much broader applicability. For two of the groups listed in the first section of Table 8.1 Chemical Abstracts has used prefix names other than those given in the 1965 IUPAC Rules: iodoso (in place of iodosyl for —10 and iodoxy (in place of iodyl) for —10 . The IUPAC names are to be preferred, however, for general use and were adopted by Chemical Abstracts in 1972. When all or nearly all of the hydrogen atoms in an organic compound have been replaced by halogen, citation of a locant for each halogen atom may often be avoided by use of the special multiplying prefix per (1). This prefix denotes replacement of all hydrogen atoms in a parent compound or substituting group by halogen atoms of a single kind, with the exception of hydrogen whose replacement would alter the identity of a functional group, as in perfluoro-l-butanol for F 3 C C F 2 C F 2 C F 2 O H and perchloroethyl for CI3CCCI2—. Although elimination of lengthy series of locants in this manner results in worthwhile simplification of names, usage of per has unfortunately been loose and inconsistent to date. In recent years, accelerated research on highly fluorinated organic compounds has increased the need for new rules, and the Nomenclature Committee of the Division of Fluorine Chemistry of the American Chemical Society has now prepared a proposal whereby use of the prefix perfluoro would be abandoned in favor of the letter prefix F (italicized). The meaning of F would be similar to that given above for per, and the principle could, of course, be extended to the other halogens. The proposal, still under review by other nomenclature committees, has not yet been officially accepted by the Society. 2
A few trivial names for simple, commonly occurring polyhalogen compounds, as shown in the examples below, are acceptable, but systematic names are to be preferred. However, the name "nitroglycerin" for 1,2,3-propanetriyl trinitrate should be abandoned, as should "chloropicrin" for trichloronitromethane. Esters of halogen oxoacids and nitrogen oxoacids are named as such —e.g., tert-buvyl hypochlorite and ethyl nitrate.
In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
Halogens, Nitros, Nitrosos, Azidos
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Table 27.1. Examples of Acceptable Usage 1.
CH I
Iodomethane Methyl iodide
2.
CH =
