skip to main content


Title: Vibrational Raman optical activity of bicyclic terpenes: comparison between experimental and calculated vibrational Raman, Raman optical activity, and dimensionless circular intensity difference spectra and their similarity analysis: Vibrational Raman optical activity of bicyclic terpenes
NSF-PAR ID:
10035766
Author(s) / Creator(s):
 ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Journal of Raman Spectroscopy
Volume:
48
Issue:
2
ISSN:
0377-0486
Page Range / eLocation ID:
305 to 313
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Experimental vibrational Raman and Raman optical activity (ROA) spectra for diacetyl L‐tartaric acid (DAT), two of its esters, namely, monomethyl and lauryl esters (T1OH and T12OH), and corresponding sodium salts (DATNa, T1ONa, and T12ONa), are measured. T12OH and T12ONa represent the first chiral surfactants investigated using ROA spectroscopy. The quantum chemical (QC) predictions using B3LYP functional and 6‐311++G(2d,2p) basis set are used to interpret the ROA spectra for DAT, DATNa, T1OH, and T1ONa. It is found that the use of implicit solvation, as represented in polarizable continuum model (PCM), for predicting the experimental ROA spectra in aqueous solutions is inadequate for DAT and T1OH. However, the same PCM predicts the experimental ROA spectra satisfactorily for the DATNa and T1ONa. This favorable observation for the latter is attributed to the absence of intra‐ and inter‐molecular hydrogen bonding interactions for sodium salts in aqueous solutions. The overwhelming number of conformations resulting from 12‐carbon alkyl chain, in T12OH and T12ONa, makes it impractical to undertake QC predictions for them. Nevertheless, it is found that the predictions made for shorter alkyl chain analogs, namely, T1OH and T1ONa, may be used to explain the experimental ROA spectra of T12OH and T12ONa. The current work highlights the importance of converting carboxylic acids to corresponding sodium salts and of QC predictions for shorter achiral alkyl chain analogs to interpret the ROA spectra of chiral surfactants that contain long achiral alkyl chains.

     
    more » « less
  2. Abstract

    The importance of the electric‐dipole—electric‐quadrupole polarizability contribution to the vibrational Raman optical activity (VROA) and dimensionless circular intensity difference spectra of (1S)‐camphor is examined. The spectra are simulated with and without this tensor contribution using density functional theory calculations, and similarity is evaluated for each against the experimental spectra. Careful examination of the comparison between experimental and calculated spectra reveals multiple vibrational bands, in the ~1,130–950 cm−1region, originating from −C–H bending vibrations that are dominated by the electric‐dipole—electric‐quadrupole polarizability contributions. The similarity overlap analysis also reveals that the similarity overlap between experimental and predicted spectra in the measured spectral range increases, by up to 12%, when electric‐dipole—electric‐quadrupole polarizability contributions are included. The negative VROA band at 1,125 cm−1in the experimental spectrum of (1S)‐(‐)‐camphor can only be reproduced in the predicted spectra when electric‐dipole—electric‐quadrupole polarizability contribution is included. Investigations on additional molecules indicated that (a) two experimental VROA bands of (1S,4R)‐(+)‐fenchone at ~1,740 and 220 cm−1originate from dominating electric‐dipole—electric‐quadrupole polarizability contribution and (b) the symmetric and antisymmetric ring deformation modes of dimethyloxirane have dominating electric‐dipole—electric‐quadrupole polarizability contribution. These observations establish the importance of electric‐dipole—electric‐quadrupole polarizability contribution to VROA for the first time.

     
    more » « less