Circular dichroism studies of optically active 1,3-dioxolan-4-ones in the vacuum ultraviolet region

The circular dichroism spectra of substituted 1,3-dioxolan-4-ones in the gas phase from 230-160 nm are reported. The Cotton effect sign in the n-π ^* region is dependent of the conformational equilibrium of the five-membered ring. Molecular mechanics (MM2) calculations show that the envelope conformer with bulky substituents in equatorial positions is the most preferred conformation. The circular dichroism corresponding to the Rydberg transitions is less conformationally dependent. Comparison of the dioxolanone (1) and the analogous dioxolane (6) spectra shows that the Rydberg transitions are mainly due to the promotion of electrons from the diether moiety.