The study of the aromaticity and the rotational isomerism of 6-di-methylaminofulvenes by nuclear magnetic resonance spectroscopy

Abstract

The energy barriers restricting rotation about the C(6)–N bond and the C(1)–C(6) bond of a number of 6-dialkylaminofulvenes have been examined using nuclear magnetic resonance spectroscopy. The steric and electronic effects of substituents upon the rotational barriers are discussed, and it is found that solvent effects are consistent with a dipolar transition state for rotation about the C(1)–C(6) bond. From the magnitude of the C(6)–N rotational barrier in 6-dimethylaminofulvene and previous estimates of the delocalisation energy of simple fulvenes, it is concluded that 6-dimethylaminofulvenes possess a substantial delocalisation energy of the order of 25–32 kcal. mole^–1.