The cyclopropa[b]naphthalene electron donor: nonplanar 8π 7C cycloheptatrienylidene derivatives

Dipole moment measurements and calculations show the cyclopropa[b]naphthalene moiety to be an electron donor that is stronger than cycloheptatriene. Crystallographic analyses of cycloheptatrienylidenecyclopropa[b]naphthalenes, with and without electron donating substituents in the cycloproparene, have the seven-membered ring resisting imposition of 8π 7C antiaromaticity by bending significantly out of the plane that carries the cycloproparene. The extent of this distortion depends upon the level of electron donation from the cycloproparene.