# 22.1: Nomenclature of Arenes

The naming of benzene derivatives was considered in Section 3-5 and is relatively straightforward. However, many benzene derivatives have acquired trivial names, and we draw your attention to a few of these below. The accepted name for the $$\ce{C_6H_5}-$$ group as a substituent is phenyl.

The more complex ring systems having two or more fused benzene rings have nonsystematic names and illogical numbering systems. They are described as polynuclear aromatic hydrocarbons, the three most important examples being naphthalene, anthracene, and phenanthrene. In anthracene the rings are connected in a linear manner, whereas in phenanthrene they are connected angularly:

The accepted numbering system for these hydrocarbons is as shown in the structures. The 1- and 2-positions of the naphthalene ring sometimes are designated as $$\alpha$$ and $$\beta$$, but we prefer not to use these designations. Some illustrative substitution products are:

The names that have been give to these and other more elaborate types of polynuclear aromatic hydrocarbons are for the most part distressingly uninformative with respect to their structures.$$^1$$

$$^1$$A thorough summary of names and numbering systems has been published by A. M. Patterson, L. T. Capell, and D. F. Walker, Ring Index, 2nd ed., American Chemical Society, 1960. Less complete but useful summaries are given in various handbooks of chemistry.