Chiral terpenes in different phases: R-(−)-camphorquinone studied by IR–Raman–VCD spectroscopies and theoretical calculations

Abstract

R-(-)-camphorquinone is a bicyclical terpenoid with many usages and application in different fields. Different experimental and theoretical works reveal that there is only one stable conformer of this chiral chemical species in agreement to the sterical restriction that the bicycle introduces. In the current work, from a complete assignment of the vibrational IR and Raman spectra, we are able to explain the VCD spectrum of the title compound. The recorded spectra of R-(-)-camphorquinone in different phases have been analyzed and compared: the first one in CCl 4 solution, the second one using Nujol and Fluorolube suspensions and the third one using thin films. Finally, to study the coupling between the two C=O stretching normal modes, a NBO analysis is performed. The present work reveals that IR, Raman and VCD, combined with quantum chemical calculations, are helpful complementary techniques to characterize chiral systems, as terpenes, in different phases.

A touch of lavender: gas-phase structure and dynamics of the monoterpene linalool validated by microwave spectroscopy

“…5,6 The only currently available gas-phase structure of a terpene is that on perillaldehyde, a cyclic monoterpene. 7 Almost no reports on gas-phase structures of acyclic monoterpenes have been published except for the millimeter-wave measurements of linalool, 8 geraniol, and verbenone 9 which were very recently recorded, but for which no assignments are available in the literature. This might be due to the fact that even smallest acyclic terpenes contain a large number of atoms and possess many possible conformers with energy differences below 10 kJ/mol.…”

Analysis of thyme essential oils using gas-phase broadband rotational spectroscopy

“…For linalool, we recorded the 8-18 GHz range using chirps of 2.5 GHz spectral width. The microwave chirps were created by an arbitrary waveform generator (AWG), amplified with a 300 W traveling wave tube amplifier (2-8 GHz) or a 50 W solid-state amplifier (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) and then broadcasted into the vacuum chamber using a horn antenna. The molecular signal was collected in the time domain as a free induction decay (FID).…”

“…8 Rotationally resolved high-resolution molecular spectroscopy offers an inherent advantage for mixture analysis because even very similar molecules can be unambiguously identified and differentiated due to its high structure sensitivity. High-resolution rotational spectroscopy in the gas phase (also denoted as microwave or molecular rotational resonance (MRR) spectroscopy) has been used to study the structures of several monoterpenes, for example linalool, 10 carvone, 11,12 fenchone, 13 camphor 14,15 or pulegone. 16 Additionally, the chiral analysis of conformational mixtures 12 and mixtures of different terpenes 17 has been demonstrated with a combination of broadband rotational spectroscopy and the chirality-sensitive microwave three-wave-mixing (M3WM) technique.…”

Study of the Photoinduced Supramolecular Chirality in Columnar Liquid Crystals by Infrared and VCD Spectroscopies

“…Though vibrational circular dichroism (VCD) spectroscopy has been known since the 1970s, − it has been in the last 2 decades when this technique has taken a special relevance in the study of chiral chemical species and materials. In the decade of the 1990s, Stephens and co-workers , developed the theoretical framework that allows simulating the VCD spectra of enantiomers using quantum chemical calculations and the determination of absolute configurations and conformational landscapes − of small molecules in solution. Also, the commercialization of VCD instruments in these 15 last years has allowed this technique to become available in an increasing number of laboratories worldwide. − …”