Fortunately I was finally able to publish my results on the conformational analysis of δ-lactones at the beginning of 2013:
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 C2-symmetrical for the parent compound, which is achiral, and C1-symmetrical for all methylated δ-lactones, which are chiral.
F. Weber, R. Brückner, Chemistry – A European Journal 2013, 19, 1288-1302. DOI: 10.1002/chem.201202988
As a part of a recent presentation on the topic I created videos where the viewer can take a ride on the two “Roller Coaster Diagrams” introduced in the article:
Moving version of the Roller Coaster Diagram of δ-valerolactone:
Moving version of the Roller Coaster Diagram of 5-methyl-δ-valerolactone:
The full presentation (password protected) can be downloaded here.