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General Principles of Organic Nomenclature

R-1.0 Introduction

Systematic naming of an organic compound generally requires the identification and naming of a parent structure. This name may then be modified by prefixes, infixes, and, in the case of a parent hydride, suffixes, which convey precisely the structural changes required to generate the actual compound from the parent structure.

Most commonly, a parent structure is a parent hydride, i.e., a structure containing, besides hydrogen, either a single atom of an element, for example, phosphane; a number of atoms (alike or different) linked together to form an unbranched chain, for example, cyclohexane, pyridine, naphthalene, and quinoline. It is sometimes convenient to employ parent hydrides, of more complex structure such as ring assemblies or ring/chain systems, for example, biphenyl, styrene, ferrocene, and cyclophanes, and to include structures with implied stereochemistry (stereoparents), for example, 5-cholestane . Rules for naming parent hydrides are given in R-2; in addition, a special class of parent structures termed functional parents, for example, phosphinic acid, is considered in R-3.3. Examples of parent structures are shown below:











Acetic acid

Phosphinic acid
In order to generate the parent structure from a molecule to be named, various formal operations must be carried out. For example, in naming the structure below,

the parent hydride "pentane" is formally derived by replacing the oxygen and chlorine atoms by the appropriate number of hydrogen atoms. For constructing a name, this formal operation is reversed; the prefix "chloro-" and the suffix "-one" indicating substitution of hydrogen atoms of pentane are attached to the parent hydride name, giving the name 5-chloropentan-2-one. Prefixes and suffixes can represent a number of different types of formal operations on the parent structure. These are defined in R-1.2. Frequently, the prefix or suffix denotes the attachment of a characteristic group, for example, "oxo-" or "-one" for =O; lists of such affixes are given in R-3.2. A prefix may describe a group which is derived from a parent hydride, for example, pentan-1-yl or pentyl for (from pentane); such prefixes are described in R-2.5.

The substitutive operation, described in R-1.2.1, is the operation used most extensively in organic nomenclature. Indeed, the comprehensive nomenclature system based largely on the application of this operation to parent structures is, for convenience, termed "substitutive nomenclature", although this system also involves many of the other types of operations described in R-1.2. Examples of this and other nomenclature operations are shown in Table 1.

In constructing the names described in R- (formerly called "radicofunctional names"), the characteristic group of the compound is expressed as a functional class name, and is usually cited as a separate word rather than as a suffix. In these recommendations, however, names obtained by a substitutive operation are preferred.

The replacement operation can be used for naming organic compounds in which skeletal atoms of a parent structure are replaced by other skeletal atoms, or in which oxygen atom and/or hydroxy groups of characteristic groups are replaced by other atoms or groups.

It is very important to recognize that, in general, the rules of organic nomenclature are written in terms of classical valence bonding and do not imply electronic configurations of any kind.

Examples of naming structures in several ways are shown in Table 1.

Full details of the way in which parent names may be combined with appropriate prefixes and suffixes are given in R-4 (Name Construction); rules for selection of a unique systematic name, if required, will be described in a separate document. Methods for the specification of stereochemistry are given in R-7 and those for denoting isotopic modification are described in R-8.

See Also:
R-1.1 Bonding Number
R-1.2 Nomenclature Operations
R-1.3 Indicated Hydrogen

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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