Conformational analysis and CD calculations of methyl-substituted 13-tridecano-13-lactones

Conformational models covering an energy range of 3 kcal/mol were calculated for (13S)-tetradecano-13-lactone (3), (12S)-12-methyltridecano-13-lactone (4). and (12S,13R)-12-methyltetradecano-13-lactone (8), starting from a semiempirical Monte-Carlo search with AM1 parametrization. and subsequent optimization of the 100 best conformers at the 6-31G*/B3LYP and then the TZVP/B3LYP level of density-functional theory. CD Spectra for these models were calculated by the time-dependent DFT method with the same functional and basis sets as for the ground-state calculations and Boltzmann weighting of the individual conformers. The good correlation of the calculated and experimental spectra substantiates the interpretation of these conformational models for the structure-odor correlation of musks. Furthermore. the application of the quadrant ride in the estimation of the Cotton effect for macrolide conformers is critically discussed.