Variation of the π‐electron delocalization in exocyclically substituted heptafulvene derivatives

Abstract

Abstract Eleven mono‐ and eight di‐exocyclically substituted heptafulvene derivatives were optimized at the B3LYP/6–311+G** level of theory. The aromaticity indices REC (ring energy content), Schleyer's NICS, 3 He NMR chemical shift and anisotropy of magnetic susceptibility and the geometry based descriptor HOMA were used to estimate the extent of cyclic π‐electron delocalization due to the substituent effect. A dramatic variation of these indices was found for electron‐accepting substituents indicating great sensitivity of the π‐electron structure of the ring. In the case of monosubstituted derivatives all indices exhibit a perfect or at least very good equivalence, whereas for disubstituted species the mutual correlations are markedly worse. Copyright © 2003 John Wiley & Sons, Ltd.