Chiroptical Properties of 2-Chloropropionitrile

Abstract

(S)-(-)-2-chloropropionitrile has been prepared from (S)-(+)-alanine, and the ORD curves have been obtained in several solvents and in the gas phase. A reaction field extrapolation of the solution data to the gas phase led to an estimated value of [alpha]D = -21 degrees, whereas the interpolated gas phase value is -8 degrees. The specific rotation was found to be temperature dependent in ethylcyclohexane solution over the range 0-100 degrees C. Although rotation of the methyl group leads to large calculated effects on the specific rotation, it does not lead to the temperature dependence. Rather, a low frequency mode at 224 cm(-1) was found to be responsible. This is a mixed mode involving methyl torsion and C-C[triple bond]N bending. The specific rotations calculated at the B3LYP/aug-cc-pVDZ level including electric field dependent functions are in very good agreement with the measured gas phase values.

The effects of conformation and solvation on optical rotation: Substituted epoxides

“…This would tend to place doubts on the analyses of optical activity contributions in EPB, suggesting that the conformer specific [a] k,h parameters are in error or that complete exclusion of vibrational dynamics is an oversimplification. 25,[35][36][37][38][39] The disparate behavior seen for the three epoxide systems targeted by the present study might also reflect the greater degrees of conformational freedom available to the ethyl group of EPB as opposed to the less flexible halomethyl substituents of ECH and EFH.…”

“…While the restriction of calculations to localized conformer geometries greatly facilitates evaluation of ensemble-averaged properties, this approximation has excluded vibrational degrees of freedom and their potentially important influence upon chiroptical effects. 25,[35][36][37][38][39]61,62 Likewise, our theoretical description of solvation has been limited to an implicit (continuum dielectric) model that neglects the detailed nature of solute-solvent interactions in the cybotactic region. This treatment has enabled solvent-mediated changes in conformer structures and populations to be estimated, but attendant modifications in chiroptical behavior caused by the surrounding medium (as reflected in the dynamical response of the solvent to oscillating electric and magnetic fields) 51 have not been taken into account.…”

Molecular Structure Determination Using Chiroptical Spectroscopy: Where We May Go Wrong?

“…77 It should also be kept in mind that in the analysis of experimental ORs using quantum chemical predictions, vibrational contributions can influence the signs and magnitudes of predicted ORs. [78][79][80] Shifting the discussion to a different aspect, errors associated with experimental ORs are often not reported in the literature, although a procedure for estimating the errors in conventional polarimetric measurements has been suggested. 81 The lack of information on errors in experimental ORs poses problems in assessing the precision in the reported values and also in estimating the agreement between quantum chemically predicted and experimentally observed OR values.…”

Comparison of measured and predicted specific optical rotation in gas and solution phases: A test for the polarizable continuum model of solvation

“…[16][17][18][19][20][21][22] Despite extensive efforts, such large effects have eluded a robust theoretical characterization. The work of the Vaccaro group on the measurement of dispersive chiroptical signatures in the vapor phase by means of cavity ring-down polarimetry (CRDP) has revealed unexpectedly large changes in the magnitude and even the sign of α ½ T λ upon transferring chiral species from the vacuum to the condensed phase.…”