Far-infrared, Raman, and dispersed fluorescence spectra, vibrational potential energy surface, and the anomeric effect of 1,3-benzodioxole

The far-infrared and Raman spectra of 1,3-benzodioxole vapor have been reco rded and analyzed. Forty-one infrared and six Raman bands were assigned to transitions between the various ring-puckering energy levels in the ground and excited ring-napping states. The determination of the energy levels was assisted by analysis of the single vibronic level fluorescence spectra of the jet-cooled molecules. The puckering levels change substantially in the napping excited state, indicating substantial interaction between the two v ibrational modes. From the spectroscopic data, a two-dimensional vibrationa l potential energy surface was determined. This has a barrier to planarity of 164 cm(-1) and energy minima at puckering and napping angles of +/-24 de grees and +/-3 degrees, respectively. This molecule has a lower barrier to planarity than 1,3-dioxole, reflecting the influence of the benzene ring on the anomeric effect. Nevertheless, the anomeric effect is clearly the orig in of the nonplanarity of this bicyclic ring system.