Configurational and conformational analysis of chiral molecules using IR and VCD spectroscopies: spiropentylcarboxylic acid methyl ester and spiropentyl acetate.
The chiral monosubstituted derivatives of spiropentane, spiropentylcarboxylic acid methyl ester, 1, and spiropentyl acetate, 2, have been synthesized in optically active form. Configurational and conformational analysis of 1 and 2 has been carried out using infrared (IR) and vibrational circular dichroism (VCD) spectroscopies. Analysis of the experimental IR and VCD spectra has been carried out using ab initio density functional theory (DFT). For both 1 and 2, DFT predicts two populated conformations. Comparison to experiment of the conformationally averaged IR and VCD spectra of 1 and 2, predicted using DFT, provides unequivocal evidence of the predicted conformations and yields the absolute configurations R(-)/S(+) for 1 and R(+)/S(-) for 2. These absolute configurations are consistent with the R(-)/S(+) absolute configuration of spiropentylcarboxylic acid, assigned previously via X-ray crystallography of its alpha-phenylethylammonium salt.
Devlin
F J
FJ
Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, USA.
Stephens
P J
PJ
Osterle
C
C
Wiberg
K B
KB
Cheeseman
J R
JR
Frisch
M J
MJ