Revised Section F: Natural Products and Related Compounds (IUPAC Recommendations 1999)

RF-5. Replacement of Skeletal Atoms

Continued from RF-4.7 Combinations of Prefixes for Modifying a Fundamental Parent Structure

Contents of this section


RF-5. Replacement of Skeletal Atoms

Replacement of skeletal atoms in parent structures whose names are formed according to RF-3 and RF-4 above is indicated by extending the principles of organic replacement nomenclature [see rules B-4 (ref 2), C-0.6 (ref 2) and R-2.3.3.2 (ref 3)]. error details

RF-5.1. Replacement of a Carbon Atom in a Parent Structure

The replacement of a carbon atom in the skeletal system of a parent structure by a heteroatom is described by appropriate replacement "a" prefixes [see R-9.3 (ref 3)]. This procedure is used even though the parent structure may already be a heterocycle. The numbering of the parent structure is retained.

Examples:

3-Azaambrosane2-Thia-5α-androstane


6,8-Dioxamorphinan

RF-5.2. Replacement of a Heteroatom in a Parent Structure

The replacement of a heteroatom in a parent structure of a natural product by a carbon atom is described by the replacement prefix "carba". The original numbering is retained. If the heteroatom in the parent structure is unnumbered, the replacing carbon atom is numbered by affixing the letter "a" to the locant of the immediately adjacent lower numbered skeletal atom. If the immediately adjacent lower numbered skeletal atom is a "homo" atom, the letter "b", "c", etc., as appropriate is used. Stereochemical configuration at the new carbon skeletal atom is described by methods for specifying additional stereochemistry (see RF-10.2).

Examples:

(4βH)-4-Carbayohimban error details16a,22a-Dicarba-5β-spirostan

RF-5.3. Replacement of a Heteroatom in a Parent Structure by Another Heteroatom

Replacement of a heteroatom in a parent structure by another heteroatom is denoted by the appropriate replacement ("a") prefix.

Example:


1-Thiaergoline

RF-5.4. Indicated Hydrogen

When the replacement of a skeletal atom in a portion of the structure of a fundamental parent structure that contains the maximum number of noncumulative double bonds or an extended conjugated system of double bonds results in the creation of a saturated skeletal position, that position is indicated by the symbolism of indicated hydrogen.

Examples:

4H-1-Oxamorphinan2H-5-Thiaporphyrin
(the name porphyrin implies two saturated positions normally shown at 21 and 23)


References for this section

2. International Union of Pure and Applied Chemistry, Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F, and H, l979 edition, Pergamon Press, Oxford, 1979.

3. International Union of Pure and Applied Chemistry, A Guide to IUPAC Nomenclature of Organic Compounds, Blackwell Scientific Publications, Oxford, 1993. [Corrections see Pure Appl. Chem., 71, 1327-1330 (1999).]


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