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preface to fifteenth edition

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1.20 SECTION 1<br />

attached <strong>to</strong> one another, then the chain chosen as parent should carry the largest number of the<br />

characteristic group. If necessary, the selection is continued as in rule 1.<br />

4. If the characteristic group occurs only in one cyclic system, that system is chosen as the parent.<br />

5. If the characteristic group occurs in more than one cyclic system, that system is chosen as parent<br />

which (a) carries the largest number of the principal group or, failing <strong>to</strong> reach a decision, (b) is<br />

the senior ring system.<br />

6. If the characteristic group occurs both in a chain and in a cyclic system, the parent is that portion<br />

in which the principal group occurs in largest number. If the numbers are the same, that portion<br />

is chosen which is considered <strong>to</strong> be the most important or is the senior ring system.<br />

7. When a substituent is itself substituted, all the subsidiary substituents are named as prefixes and<br />

the entire assembly is regarded as a parent radical.<br />

8. The seniority of ring systems is ascertained by applying the following rules successively until a<br />

decision is reached: (a) all heterocycles are senior <strong>to</strong> all carbocycles, (b) for heterocycles, the<br />

preference follows the decision process described under Heterocyclic Systems, p. 1.11, (c) the<br />

largest number of rings, (d) the largest individual ring at the first point of difference, (e) the<br />

largest number of a<strong>to</strong>ms in common among rings, (f) the lowest letters in the expression for ring<br />

functions, (g) the lowest numbers at the first point of difference in the expression for ring junctions,<br />

(h) the lowest state of hydrogenation, (i) the lowest-numbered locant for indicated hydrogen,<br />

(j) the lowest-numbered locant for point of attachment (if a radical), (k) the lowest-numbered<br />

locant for an attached group expressed as a suffix, (l) the maximum number of substituents cited<br />

as prefixes, (m) the lowest-numbered locant for substituents named as prefixes, hydro prefixes,<br />

-ene, and -yne, all considered <strong>to</strong>gether in one series in ascending numerical order independent of<br />

their nature, and (n) the lowest-numbered locant for the substituent named as prefix which is cited<br />

first in the name.<br />

Numbering of Compounds. If the rules for aliphatic chains and ring systems leave a choice, the<br />

starting point and direction of numbering of a compound are chosen so as <strong>to</strong> give lowest-numbered<br />

locants <strong>to</strong> these structural fac<strong>to</strong>rs, if present, considered successively in the order listed below until<br />

a decision is reached. Characteristic groups take precedence over multiple bonds.<br />

1. Indicated hydrogen, whether cited in the name or omitted as being conventional<br />

2. Characteristic groups named as suffix following the ranking order of Table 1.7<br />

3. Multiple bonds in acyclic compounds; in bicycloalkanes, tricycloalkanes, and polycycloalkanes,<br />

double bonds having priority over triple bonds; and in heterocyclic systems whose names end in<br />

-etine, -oline, or -olene<br />

4. The lowest-numbered locant for substituents named as prefixes, hydro prefixes, -ene, and -yne,<br />

all considered <strong>to</strong>gether in one series in ascending numerical order<br />

5. The lowest locant for that substituent named as prefix which is cited first in the name<br />

For cyclic radicals, indicated hydrogen and thereafter the point of attachment (free valency) have<br />

priority for the lowest available number.<br />

Prefixes and Affixes. Prefixes are arranged alphabetically and placed before the parent name;<br />

multiplying affixes, if necessary, are inserted and do not alter the alphabetical order already attained.<br />

The parent name includes any syllables denoting a change of ring member or relating <strong>to</strong> the structure<br />

of a carbon chain. Nondetachable parts of parent names include

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