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Introduction

R-0.1.8 Order of prefixes

In general, two types of prefixes are used in naming organic compounds, detachable and nondetachable; each may be subdivided further. For example, two kinds of nondetachable prefixes are those modifying the skeletal structure of a parent, such as "homo-" and "nor-", and those indicating replacement of skeletal atoms of a parent hydride, the socalled "a" prefixes, such as "aza-" and "oxa-". Each class of prefix has its preferred position in front of the name of a parent structure and is ordered as discussed in the following subsections.

R-0.1.8.1 Nondetachable prefixes that modify the skeletal structure of a parent hydride are cited in alphabetical order immediately preceding the name of the parent hydride. This type of prefix is found commonly in names of natural products (stereoparents) and is discussed more fully in Section F of the IUPAC Nomenclature of Organic Chemistry; however, they are occasionally encountered in trivial and semisystematic names, for example, homocubane.

R-0.1.8.2 Nondetachable prefixes ("a" replacement terms commonly known as "a" prefixes) that indicate replacement of skeletal atoms of a parent hydride are cited in the order of appearance in R-9.3, immediately preceding nondetachable skeleton-modifying prefixes (see R-0.1.8.1), if any, for example, .

R-0.1.8.3 Detachable prefixes describing substituents are cited preceding nondetachable prefixes (see R-0.1.8.1 and R-0.1.8.2), if any, and are alphabetized as follows:

(a) Simple prefixes (i.e., those describing atoms and unsubstituted substituents) are arranged alphabetically; multiplying affixes, if necessary, are then inserted and do not alter the alphabetical order already established.

Examples to R-0.1.8.3(a)

(b) The name of a prefix for a substituted substituent is considered to begin with the first letters of its complete name.

Example to R-0.1.8.3(b)

(Difluorobutyl as a complete substituent is alphabetized under "d".)

(c) When two or more prefixes consist of identical roman letters, priority for citation is given to that group which contains the lowest locant at the first point of difference.

Example to R-0.1.8.3(c)

(d) o- (ortho), m- (meta), and p- (para) substituents, if otherwise identical, are arranged in that order (the same as their numerical equivalents, 2-, 3-, and 4-, respectively).

Example to R-0.1.8.3(d)

R-0.1.8.4 Subtractive prefixes (such as anhydro-, dehydro-, demethyl-) have been used as "detachable" or "nondetachable" in previous editions of the IUPAC Nomenclature of Organic Chemistry, but in these recommendations, they are presented as nondetachable.

Example to R-0.1.8.4

(nondetachable)

R-0.1.8.5 Additive prefixes. According to the previous edition of the IUPAC Nomenclature of Organic Chemistry (C-16.11), the additive prefixes "-dihydro-", "tetrahydro-", etc., could be either detachable and alphabetized among the set of substitutive prefixes, or nondetachable and cites after the substitutive prefixes. In this guide these prefixes are presented as nondetachable.

Example to R-0.1.8.5

4-Oxo-1,2,3,4-tetrahydronaphthalene-1-carboxylic acid

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This HTML reproduction is as close as possible to the published version [see IUPAC, Commission on Nomenclature of Organic Chemistry. A Guide to IUPAC Nomenclature of Organic Compounds (Recommendations 1993), 1993, Blackwell Scientific publications, Copyright 1993 IUPAC]. If you need to cite these rules please quote this reference as their source.

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