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-tetrahydrodibenzo[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 1,4,7,10,13,16-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-(15) and 1,4,7,10-(16) 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.