Experimental and theoretical determinations of bond lengths in naphthalene, anthracene and other hydrocarbons

Recent independent determinations by X-ray crystallography of the C-C bond lengths in naphthalene and anthracene are shown to agree well. The experimental values agree to about 0$\cdot$01 $\overset{\circ}{\mathrm A}$ with both the simple molecular orbital and simple Pauling theories. These theories also make satisfactory predictions for 1$\cdot$2:8$\cdot$9-dibenzacridine and chrysene (except for the bond most affected by steric hindrance). The agreement between the two theories for aromatic molecules is traced to a correlation of their respective bond orders. For ethylene, butadiene, cyclooctatetraene and diphenyl the Pauling method is superior to the simple m.o. method.