SUBSTITUENT EFFECTS ON THE CONFORMATIONAL EQUILIBRIUM OF 1,3,5,7-CIS-TETRAOXADECALIN SYSTEMS - FORCE-FIELD CALCULATIONS VERSUS EXPERIMENTALRESULTS

Conformer populations of a number of 1,3,5,7-cis-tetraoxadecalins have been studied by H-1 NMR spectroscopy. While the unsubstituted 4 prefe rs the proximal conformation, all 4,8 disubstituted derivatives 5 pref erred the distal conformation. This was most marked for the di-azidome thyl derivative 5g. Force field calculations were shown to reproduce o nly roughly the trends of the conformer equilibria. Changing the solve nt from toluene-D-8 to more polar solvents increases the population of the proximal conformer.