Vibrational circular dichroism as a criterion for local-mode versus normal-mode behavior. Near-infrared circular dichroism spectra of some monoterpenes

Vibrational circular dichroism (VCD) spectra are presented for (S)-(-)-limonene, (R)-(+)-limonene, (S)-(- )-perillyl alcohol, (S)-(-)-perillaldehyde, (R)-( + )-p-menth-1-ene, and (R,R)-( + )-p-menth-1-en-9-ol in the region 130G-800 nm. Bisignate couplets are observed for all six compounds; these are ascribed to overtones associated with CH stretching vibrations. The ordering of the signs in the couplets correlates with the known absolute configuration in all cases. The presence of such couplets for the terpenes just mentioned, and the absence of such couplets for closely related cyclic compounds, is interpreted in terms of normal-mode versus local-mode behavior.