Fourier transform vibrational circular dichroism from 800 to 10,000 cm−1: Near-IR-VCD spectral standards for terpenes and related molecules

Near-infrared (near-IR) and mid-infrared (mid-IR) vibrational circular dichroism (VCD) spectra in the region 800–10,000 cm−1 were recorded for nine enantiomeric pairs (or enantiomer and racemate pairs) of molecules with three ChiralIR Fourier transform (FT) VCD spectrometers equipped with various light sources and detectors and modified for dual polarization modulation (DPM) operation. Correlations across these sets of spectra permit conclusions regarding expected VCD intensities in the near-infrared compared to the conventional mid-IR regions. These VCD spectra also provide spectral standards for future studies in the near-infrared region. Compared with recent near-IR measurements carried out elsewhere using dispersive instrumentation, better signal-to-noise ratios were obtained for all but the frequency region above 8000 cm−1 where VCD spectra of comparable quality were obtained. These results are the first comprehensive set of VCD spectra for a set of simple chiral molecules with continuous coverage from the mid-infrared to nearly the visible region of the spectrum. This study demonstrates that with suitably equipped FT-VCD spectrometers, VCD and IR spectra can be measured with high quality across a wide spectral range.