Local Aromaticity in Benzo- and Benzocyclobutadieno-Annelated Phenanthrenes

Abstract

The effects of benzo- and benzocyclobutadieno-(BCBD-)annelation on the local aromaticity of the central ring (X) of phenanthrene were examined. The local aromaticity of the ring X was estimated using a graph-theory-based index and two geometry-based indices. DFT calculations of phenanthrene congeners showed that many of these molecules are nonplanar, with significant steric strain. All three indices indicate that the effect of benzo-annelation is opposite to that of BCBD-annelation. The deviation of some phenanthrene derivatives from planarity does not influence the effects of annelation. This finding is in accord with some previously reported studies on the dependence of the aromaticity of the ring(s) on distortion from planarity.

Key Words:

• phenanthrene
• benzo-annelated phenanthrenes
• benzocyclobutadieno-annelated phenanthrenes
• aromaticity
• deviation from planarity

Acknowledgments

The authors thank the support of the Ministry of Science of Serbia, through Grant no. 174033 and 172016.