Conformational behaviour of medium-sized rings. Part 6. 5,6,11,12,-17,18-hexahydrotribenzo[a, e, i]cyclododecene and its 2,3,8,9,14,15- and 1,4,7,10,13,16-hexamethyl derivatives. 2,3,8,9- and 1,4,7,10-tetramethyl-5,6,11,12-tetrahydrodi benzo[a, e]cyclo-octene

Abstract

The temperature dependences of (i) the broad-band decoupled 13C n.m.r. spectrum of 5,6,11,12,17,18-hexahydrotribenzo[a.e, i]cyclododecene (1) and (ii) the 1H n.m.r. spectra of its 2,3,8.9,14,15- (2) and 1.4,7,10,13.16- (3) hexamethyl derivatives have been interpreted in terms of ring inversion between enantiomeric C2 conformations. Conformational analysis on these molecules has been carried out with the aid of strain energy calculations on selected conformations of the parent hydrocarbon (1) and its 1.4.7.1 0,13.16-hexamethyl derivative (3). Useful correlations between calculated and experimental thermodynamic parameters were found. The temperature dependences of the 1H n.m.r. spectra of the 2.3.8.9- (1 5) and 1,4,7,10- (1 6) tetramethyl derivatives of 5,6,11,12-tetrahydrodibenzo[a, e]cyclo-octene (14) have been interpreted in terms of interconversion of chair- and boat-like conformations. Strain energy calculations on selected conformations of the 1.4.7.10-tetramethyl derivative (14) have led to useful correlations between calculated and experimental thermodynamic parameters. © 1978, Royal Society of Chemistry.