Conformational analysis of δ-lactones by DFT calculations: the parent compound and its monomethyl and selected dimethyl derivatives.

The static and dynamic stereochemistry of unsubstituted δ-valerolactone, all monomethylated δ-lactones, and all nongeminally dimethylated δ-lactones was explored with the B3LYP functional and def2-TZVPP basis set. A search strategy was employed which allowed the entire conformational space of any (poly-)substituted δ-lactone to be scanned. It allowed the lowest threshold conformational interconversion pathways to be mapped. The latter can be visualized in appealingly intuitive yet unprecedented diagrams. They trace the energy versus a circular abscissa which describes the passage of the molecule through one complete conformation interchange. The respective plot is C(2)-symmetrical for the parent compound, which is achiral, and C(1)-symmetrical for all methylated δ-lactones, which are chiral.