Ring energy content of benzene rings in benzenoid hydrocarbons

Ring Energy Content of benzene rings in benzenoid hydrocarbons 

Two different values of REC for particular rings of benzene and phenanthrene result from different measurements of their molecular geometry. The different REC values for symmetrically equivalent rings in other benzenoid hydrocarbons result from the method of X-ray structure determination. If the symmetrical molecule does not lie at the symmetry element in the crystal lattice, each of the rings is measured independently and its geometry (and in turn its REC value) is biased by the another error of measurement. The differences in REC values for symmetrically equivalent 

Ring energy content Ring energy content 

Another conclusion may also be drawn. This strong dependence of REC values (as well as formerly stated EN and HOMA values) of benzene rings in the benzenoid hydrocarbons on topology may be of a key importance for understanding of the successful treatments of benzenoid hydrocarbons by the so-called graph-topological models [27]. 

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