Conformational behaviour of medium-sized rings. Part I. 5,6,11,12-Tetrahydrodibenzo[a,e]cyclo-octene (1,2,5,6-dibenzocyclo-octa-1,5-diene) and heterocyclic analogues

Abstract

The temperature dependence of the n.m.r. spectra of the eight-membered ring compound 5,6,11,12-tetrahydrodibenzo[a,e]cyclo-octene (1) and various aza- and thia-analogues [(7a–c), (8a–e), (9a–f), and (10b)] has been interpreted in terms of the interconversion of chair- and boat-like conformations. The values of the free energies of activation for these conformational changes are discussed in terms of probable transition state geometries and calculated strain energies.