Electrical and mechanical anharmonicities from NIR-VCD spectra of compounds exhibiting axial and planar chirality: The cases of (S)-2,3-pentadiene and methyl-d(3) (R)- and (S)-[2.2]paracyclophane-4-carboxylate.

The IR and Near infrared (NIR) vibrational circular dichroism (VCD) spectra of
molecules endowed with noncentral chirality have been investigated. Data for fundamental,
first, and second overtone regions of (S)-2,3-pentadiene, exhibiting axial chirality, and methyl-d3
(R)- and (S)-[2.2]paracyclophane-4-carboxylate, exhibiting planar chirality have been measured
and analyzed. The analysis of NIR and IR VCD spectra was based on the local-mode model and
the use of density functional theory (DFT), providing mechanical and electrical anharmonic
terms for all CH-bonds. The comparison of experimental and calculated spectra is satisfactory
and allows one to monitor fine details in the asymmetric charge distribution in the molecules:
these details consist in the harmonic frequencies, in the principal anharmonicity constants, in
both the atomic polar and axial tensors and in their first and second derivatives with respect to
the CH-stretching coordinates.