CH-stretching vibrational circular dichroism of α-hydroxy acids and related molecules

Vibrational Transition Current Density in (S)-Methyl Lactate: Visualizing the Origin of the Methine-Stretching Vibrational Circular Dichroism Intensity

“…These circulations occur under conditions of approximately constant electron probability density during molecular vibration, since the current feeds into itself around the atom. This pattern has been observed previously in formaldehyde, 3,10 ethylene, 10 and oxirane 12 for modes that are symmetry allowed for components of the angular momentum operator. The existence and beauty of these atomic current patterns were unknown before the implementation of vibrational TCD plots.…”

“…For four vibrations of a chiral molecule, (2S,3S)-oxirane-d 2 , we showed how TCD plots provide insight into the origins of the electronic contributions to both infrared and VCD intensity. 12 In this study, we demonstrate how TCD plots can be used to understand the differences in VCD intensity for a molecule in a variety of conformations. VCD is measured as the difference in absorbance or molar absorptivity for left and right circularly polarized infrared radiation, ∆ ) L -R .…”

“…We recently introduced a method for calculating and visualizing the flow of electron density produced by electronic excitation or nuclear motion, utilizing plots of electron transition current density (TCD) for electronic and vibrational transitions. 3,[8][9][10][11][12] The TCD vector field, which is related to the integrand of the velocityform electric dipole transition moment, gives the magnitude and direction of vibrationally generated electron density current at each point in space. In practice, this corresponds to a TCD vector at each electron density volume element in a grid of points encompassing a molecule.…”

“…Vibrational circular dichroism (VCD) intensity is proportional to the rotational strength R = Im(μ) 01 ·( m⃗ ) 10 , the scalar product of the electric dipole transition moment, (μ) 01 , originating from linear oscillation of charge, and the magnetic dipole transition moment, ( m⃗ ) 10 , originating from circular oscillation of charge, generated by the nuclear vibrational motion. − Although vibrational circular dichroism (VCD) spectra can now be calculated fairly routinely, with good agreement to experiment, − the electronic motion from which the intensities are generated cannot be deduced from such calculations. We recently introduced a method for calculating and visualizing the flow of electron density produced by electronic excitation or nuclear motion, utilizing plots of electron transition current density (TCD) for electronic and vibrational transitions. ,− The TCD vector field, which is related to the integrand of the velocity-form electric dipole transition moment, gives the magnitude and direction of vibrationally generated electron density current at each point in space. In practice, this corresponds to a TCD vector at each electron density volume element in a grid of points encompassing a molecule.…”

Hydrogen Stretching Vibrational Circular Dichroism in Methyl Lactate and Related Molecules

“…The methine-stretching TCD for the four conformations of methyl lactate has been calculated and will be reported separately. 50 Appendix: Synthetic Procedures General Procedure for Transesterification: (R)-Methyld 3 lactate. To 1.017 g of (R)-methyl lactate in 3 mL of methanol-d 4 was added 0.075 g of 10-camphorsulfonic acid, and the resulting mixture was heated at 65 °C for 24 h. Solvent was distilled from the reaction, an additional 3 mL of methanold 4 was added, and the reaction mixture was heated for an additional 24 h at 65 °C.…”