Chirality transition in the epoxidation of (−)-α-pinene and successive hydrolysis studied by Raman optical activity and DFT

Abstract

Characterization of the chirality evolution involved in chemical and biochemical reaction processes is extremely important to the understanding of the chiral catalysis mechanism. In this work, the chiral transition from the epoxidation of (-)-alpha-pinene to alpha-pinene oxide and successive hydrolysis to (-)-pinanediol has been studied as an archetype of the asymmetric catalysis by Raman optical activity (ROA) and the DFT calculation. Minor changes of the absolute configuration of the chiral products from (-)-alpha-pinene to (-)-pinanediol lead to the dramatic variation in ROA spectra indicating that the chirality is delocalized in the whole molecule rather than only concentrated on the chiral centers. The oxygen atom of alpha-pinene oxide contributes strong ROA signals while the two hydroxyl groups of (-)-pinanediol give no apparent contribution to the chirality in terms of ROA signals. Isolation of the two symmetric anisotropic invariants shows that the predominant contribution to the ROA signals stems from the electric dipole-magnetic dipole invariant, and the bond polarizability model is indeed found to be a good approximation for molecules composed of entirely axially-symmetric bonds in alpha-pinene oxide and (-)-pinanediol. This study demonstrates the feasibility of using ROA to sensitively monitor the variation of the chirality transition during the chiral reactions either in the chemical or biological system.

In situ analysis of chiral components of pichtae essential oil by means of ROA spectroscopy: experimental and theoretical Raman and ROA spectra of bornyl acetate

“…All these bands are associated with the scissoring vibrations of-CH 2 groups and the antisymmetric-CH 3 deformations and reflect the chiral environment in the bycyclic ring structure. [38] It seems that, in the experimental spectrum, there are also other noticeable features similar to those reported in the literature, such as positive peaks at 1165, 1197 and 1208 cm −1 (corresponding to theoretical bands at 1169, 1202 and 1214 cm −1 , respectively). According to our calculations, the origin of the band at 1165 cm −1 with a large positive ROA activity is the combination of predominant wagging vibrations localized at two chiral centres, that is the C 4 and C 1 carbon atoms.…”

“…Thus, among others, we can see in these spectra characteristic bands at 1688, 1659 and 1639 cm −1 due to C C stretchnig vibrations originating from 3-carene, α-pinene and probably camphene, respectivety, and well-structured marker bands for these components attributed to ring deformations at 669 cm −1 for α-pinene or 717 cm −1 for 3-carene. [12,35,38,39,41] However, above all, we are able to define several characteristic key bands for BA, which do not overlap with other principal component bands of pichtae oil (Fig. S2), including those at 1736, 1049, 839, 746, 657, 642 and 591 cm −1 described earlier (text or Table 1).…”

Vibrational spectroscopic identification of isoprene, pinenes and their mixture

“…In addition, attention may need to be paid if judging the strongest peak at 1644 cm À1 (C5 5C stretching) [39] as it also allows for peakvalue shifts according to the calculation results in this study. It is worth mentioning that the fruitful Raman peaks as a whole could still be a piece of evidence to recognize the presence of b-pinene and even likely its proportion of ingredients.…”

“…First glance could focus on the 644 cm À1 mode (ring breathing) in the experimental Raman spectrum which allows a red-shift of $14 cm À1 (i.e., a peak at 630 cm À1 ) by comparing the theoretically predicted Raman activity. It is suggested that the series of peaks at 1413 cm À1 (CH 2 scissoring), 1439 cm À1 (CH 2 scissoring), 1458 cm À1 (CH 2 scissoring, CH 3 asymmetric deformation) and 1478 cm À1 (CH 2 scissoring, CH 3 asymmetric deformation) [39] could be regarded as another fingerprint of b-pinene.…”

Chiral Sulfur Compounds Studied by Raman Optical Activity: tert‐Butanesulfinamide and its Precursor tert‐Butyl tert‐Butanethiosulfinate

“…[43][44][45][46] As a given chiroptical spectroscopic method may not give complete and entirely correct structural information for a given molecule, the simultaneous use of more than one spectroscopic method may provide the complete information. [62][63][64][65] The chiroptical variant of Raman scattering, ROA, is proven to be an effective tool to determine the configuration, conformation, and behavior of chiral molecules in recent years, 43,45,[66][67][68][69][70][71][72][73][74][75][76] and thus a presumably good candidate for the study of sulfur chirality. 48 The high polarizability of sulfur atom makes Raman spectroscopy a sensitive technique to identify sulfur compounds, and much effort has been focused on correlation between C-S, S-S stretching modes and the S-S dihedral angle.…”