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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.
(b) The name of a prefix for a substituted substituent is considered to begin with the first letters of its complete name.Examples to R-0.1.8.3(a)
(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(b)
(Difluorobutyl as a complete substituent is alphabetized under "d".)
(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(c)
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 ChemistryExample to R-0.1.8.3(d)
, but in these recommendations, they are presented as nondetachable.
R-0.1.8.5 Additive prefixes. According to the previous edition of the IUPAC Nomenclature of Organic ChemistryExample to R-0.1.8.4
(nondetachable)
(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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