Theoretical investigation of Raman optical activity signatures of Tröger's base.

The Raman and VROA spectra of (S,S)-Tröger's base are simulated. We mainly discuss the peaks in the 1140-1400 cm(-1) wavenumber range where an intense VROA signature is found. In this range, nearly all of the Raman-active bands belong to the irreducible representation A (C(2) point group), whereas no such observation is made for the VROA spectrum. The vibrational normal modes associated with the peaks in this range mainly consist of wagging and twisting motions of the hydrogen atoms. From the atomic contribution patterns (ACPs) and the group coupling matrices (GCMs), one finds that the VROA backward-scattering intensities mainly arise from hydrogen and carbon atoms in the vicinity of the two chiral nitrogen atoms. The VROA signatures in the 1140-1400 cm(-1) range are therefore a fingerprint of the local chirality around the two chiral nitrogen centers.