Vibrational circular dichroism of (S,S)-[2,3-2H2]oxirane in the gas phase and in solution

1991 ◽  
Vol 69 (11) ◽  
pp. 1619-1629 ◽  
Author(s):  
Teresa B. Freedman ◽  
Kevin M. Spencer ◽  
N. Ragunathan ◽  
Laurence A. Nafie ◽  
Jeffrey A. Moore ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Gas Phase ◽  
Vibrational Circular Dichroism ◽  
Vibrational Modes ◽  
Chiral Perturbation ◽  
Linear Charge ◽  
Deuterium Substitution ◽  
Symmetry Species ◽  
Charge Oscillation ◽  
Circular Dichroïsm

Vibrational circular dichroism (VCD) spectra of an exceptionally simple chiral three-membered ring molecule, (S,S)-[2,3-2H2]oxirane, have been obtained for samples in the gas phase and in C2Cl4 and CS2 solution. The VCD band contours for the gas phase samples of this molecule with C2 symmetry follow those of the absorption spectra, with the modes of A symmetry species giving rise to bands with two sharp Q-branch maxima on either side of a distinct minimum, and the modes of B symmetry species giving rise to bands with a strong central Q-branch. The signs and relative intensities of the VCD bands can be understood in terms of chiral perturbation by the deuterium substitution of the vibrational modes of the parent oxirane molecule, which mixes modes of A1 and A2 symmetry, and modes of B1 and B2 symmetry, thus introducing angular charge oscillation about the direction of linear charge oscillation. Key words: vibrational circular dichroism, oxirane, chiral perturbation.

Vibrational Circular Dichroism Of Simple Chiral Molecules In The Gas Phase

1989 ◽  
Author(s):  
T. B. Freedman ◽  
K. M. Spencer ◽  
C. McCarthy ◽  
S. J. Cianciosi ◽  
J. E. Baldwin ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Gas Phase ◽  
Vibrational Circular Dichroism ◽  
Chiral Molecules ◽  
Circular Dichroïsm

The VCD spectrum of 2-methylthietane: measured (800–1500 cm−1) and computed with semi-empirical models

1991 ◽  
Vol 69 (2) ◽  
pp. 345-356 ◽  
Author(s):  
R. A. Shaw ◽  
N. Ibrahim ◽  
H. Wieser
Keyword(s):  
Circular Dichroism ◽  
Vibrational Circular Dichroism ◽  
Equatorial Orientation ◽  
Partial Charge ◽  
Vibrational Modes ◽  
Harmonic Force ◽  
Polar Tensor ◽  
Charge Flow ◽  
Semi Empirical ◽  
Circular Dichroïsm

The vibrational circular dichroism (VCD) spectrum (800 to 1500 cm−1) is reported for 2-methylthietane (2MT). Fixed partial charge (FPC), atomic polar tensor (APT), and charge flow (CF) methods are used to compute the VCD spectra for both stable conformers (CH3 in the axial or equatorial orientation) for the complete range of fundamental vibrations, based on 3-21G and 6-31G* harmonic force fields. The experimental and computed absorption and VCD spectra of R-(+)-2MT are compared to the previously reported spectra of R-(−)-2-methyloxetane. The success of the APT and CF models for reproducing the dominant ring stretching IR and VCD features of that compound is rationalized by a comparison of APT and FPC intensity expressions. Further comparison of the APT and FPC calculated electric dipole moment derivatives are interpreted to suggest values for the diagonal CS and CH stretching charge flow terms for 2MT. These investigations then provide a rationale for previously reported successes of the FPC model, and permit identification of specific vibrational modes of 2MT that are amenable to FPC-VCD modeling. The previously established conformational mixture of ~30% axial and 70% equatorial is shown to be in accord with FPC-VCD predictions for the most appropriate (β-CH2 wagging) mode. Key words: vibrational circular dichroism, 2-methylthietane, fixed partial charge, atomic polar tensor, charge flow

Synthesis and gas-phase vibrational circular dichroism of (+)-(S,S)-cyclopropane-1,2-2H2

1989 ◽  
Vol 111 (5) ◽  
pp. 1913-1915 ◽  
Author(s):  
Steven J. Cianciosi ◽  
Kevin M. Spencer ◽  
Teresa B. Freedman ◽  
Laurence A. Nafie ◽  
John E. Baldwin
Keyword(s):  
Circular Dichroism ◽  
Gas Phase ◽  
Vibrational Circular Dichroism ◽  
Circular Dichroïsm

Kinetics of thermal racemization of (2S,3S)-1-13C-1,2,3-d3-cyclopropane followed by vibrational circular dichroism spectroscopy

1998 ◽  
Vol 76 (6) ◽  
pp. 806-810 ◽  
Author(s):  
Teresa B Freedman ◽  
Diane L Hausch ◽  
Steven J Cianciosi ◽  
John E Baldwin
Keyword(s):  
Circular Dichroism ◽  
Gas Phase ◽  
Rate Constant ◽  
Rate Constants ◽  
Circular Dichroism Spectroscopy ◽  
Vibrational Circular Dichroism ◽  
Clear Indication ◽  
Competitive Reaction ◽  
Kinetics Of ◽  
Circular Dichroïsm

Vibrational circular dichoism spectra recorded for (2S,3S)-1-13C-1,2,3-d3-cyclopropane and for mixtures of it and the three related stereoisomers prepared through gas-phase thermal stereomutation reactions at 407°C lead to the rate constant for racemization: kα = (4k1 + 4k12) = (3.12 ± 0.04) x 10-5 s-1. This and the rate constant measured for geometrical equilibration between the two chiral and the two achiral stereoisomers of 1-13C-1,2,3-d3-cyclopropane, ki = (8k1 + 4k12) = (4.63 ± 0.20) x 10-5 s-1, give two equations in two unknowns, and allow one to solve for one-center (k1) and two-center (k12) epimerization rate constants for cyclopropane stereomutations. They are nearly equal, a clear indication of closely competitive reaction pathways.Key words: cyclopropane stereomutations, thermal epimerizations, chirality through deuterium and carbon-13 labeling, vibrational circular dichroism.

ChemInform Abstract: Synthesis and Gas-Phase Vibrational Circular Dichroism of (+)-(S,S)-Cyclopropane-1,2-2H2.

ChemInform ◽  
1989 ◽  
Vol 20 (23) ◽  
Author(s):  
S. J. CIANCIOSI ◽  
K. M. SPENCER ◽  
T. B. FREEDMAN ◽  
L. A. NAFIE ◽  
J. E. BALDWIN
Keyword(s):  
Circular Dichroism ◽  
Gas Phase ◽  
Vibrational Circular Dichroism ◽  
Circular Dichroïsm
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