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preface to fifteenth edition

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ORGANIC COMPOUNDS 1.7<br />

sequence wherever there is a choice. Anthracene and phenanthrene are two exceptions <strong>to</strong> the rule<br />

on numbering. Two examples of numbering follow:<br />

When a ring system with the maximum number of conjugated double bonds can exist in two or<br />

more forms differing only in the position of an “extra” hydrogen a<strong>to</strong>m, the name can be made<br />

specific by indicating the position of the extra hydrogen(s). The compound name is modified with<br />

a locant followed by an italic capital H for each of these hydrogen a<strong>to</strong>ms. Carbon a<strong>to</strong>ms that carry<br />

an indicated hydrogen a<strong>to</strong>m are numbered as low as possible. For example, 1H-indene is illustrated<br />

in Table 1.2; 2H-indene would be<br />

Names of polycyclic hydrocarbons with less than the maximum number of noncumulative double<br />

bonds are formed from a prefix dihydro-, tetrahydro-, etc., followed by the name of the corresponding<br />

unreduced hydrocarbon. The prefix perhydro- signifies full hydrogenation. For example, 1,2-dihydronaphthalene<br />

is<br />

Examples of retained names and their structures are as follows:<br />

Indan Acenaphthene Aceanthrene<br />

Acephenanthrene<br />

Polycyclic compounds in which two rings have two a<strong>to</strong>ms in common or in which one ring<br />

contains two a<strong>to</strong>ms in common with each of two or more rings of a contiguous series of rings and<br />

which contain at least two rings of five or more members with the maximum number of noncumu-

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