| Ab initio calculations support assignment of the vacuum ultraviolet circular dichroism (CD) of simple saccharides to 11A 1 → 21B1 and 11A 1 → 11A2 transitions centered on the oxygen atoms of the acetal group treated as two weakly coupled ether chromophores. The calculations are consistent with assignments previously made on the basis of a deconvolution of CD spectra. Estimates of the oxygen centered contributions to magnetic transition dipole moments were made.;A low energy CD band arises in 3,6- and 1,6-anhydrosugars when agreement with the experimental NaD molar rotations is achieved. It is proposed that this band is a real feature in the spectrum. The origin of the band is primarily the interaction between b1 symmetry-oriented transition dipoles in the COC groups with other transition dipoles in the molecule. Comparison with experimental spectra leads to an assignment of this band to 11A1 → 21B1 transitions centered on the COC groups.;Semiempirical calculations were performed to model the NaD molar optical rotation of 1,6- and 3,6-anhydrosugars. For 1,6-anhydrosugars, current parameters produce reasonable agreement with experimental values. For 3,6-anhydrosugars, modifications to the ether parameters had to be introduced. The most relevant included a reorientation of the bond-centered s→s* transition dipole charges in the ether chromophore to a C2v orientation, and a shift from prolate polarizability ellipsoids to general ellipsoids. These changes result in good agreement with experimental Na D molar rotations for 3,6-anhydrosugars. |
