Experimental circular dichroism and VUV spectra of substituted oxiranes and thiiranes

Abstract

Highly resolved circular dichroism spectroscopy of alkyl-substituted oxirane and thiirane chromophores was investigated in the vacuum ultraviolet region up to 9·0 eV (138 nm) using synchrotron radiation. Comparison of the gas phase and liquid phase spectra, along with results from theoretical calculations, could confirm the predicted Rydberg character of some excited states including their fine structures. The n(O)→R(3d) Rydberg transitions in chiral methyloxirane and the predicted n(S)→σ* valence transition of (S, S)-(−)-(2,3)-dimethylthiirane were detected for the first time. It could be shown that the quadrant rule for the first state previously verified for some chiral oxiranes also holds for (R)-(−)-1,2-epoxy-3-methyl-butane and (R)-(−)-1,2-epoxy-4-methyl-pentane and is found to be expandable for thiiranes. The first ns Rydberg transitions of dimethyloxirane could be fitted to a term formula.