Bond distortions in nonbenzenoid phanes

Abstract

The C–C bond alternations in syn-[2.2]azulenophane, syn-[2.2]cycloprop[f]indenophane, and [2.2]pentalenophane have been investigated by use of second-order Jahn–Teller theory and the Pariser–Parr–Pople-type SCF MO method. It has been shown that syn-[2.2]azulenophane suffers no bond distortions, whereas syn-[2.2]cycloprop[f]indenophane suffers a₂ bond alternation, which is attributed to transannular interaction. Further, in [2.2]pentalenophane and [2.2]-s-indacenophane, C_2h and D₂ bond-alternating structures are obtained, the transannular interaction stablising the D₂ more than the C_2h structures.