Enthalpy and Entropy of Conjugative Interaction in a Nearly Coplanar Styrene and Cinnamyl Radical

Abstract

Listen

Translate article

Conjugative interaction in styrenes designed to constrain the dihedral angle between the planes of the phenyl and olefinic groups near to coplanarity (21° by X-ray) is greater by 0.7 kcal mol-1 than that in a styrene in which the phenyl group is unconstrained (ad libitum) (−35° by MM2 molecular mechanical calculation). Conjugative interaction in a cinnamyl radical similarly constrained to maintain the phenyl and allyl moieties nearly coplanar (15° by MM2) is greater by 1.1 kcal mol-1 than in a cinnamyl radical in which the phenyl group is ad libitum. Efforts to separate the contribution of π-electron delocalization from the nonbonded steric factor by employing MM2 calculations proved quantitatively unsatisfactory.