Determination of the absolute configuration of chiral molecules via density functional theory calculations of vibrational circular dichroism and optical rotation: The chiral alkane D3-anti-trans-anti-trans-anti-trans-perhydrotriphenylene
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The Absolute configuration (AC) of the chiral alkane D3-anti-trans-anti-trans-anti-trans-perhydrotriphenylene (PHTP), 1, is determined by comparison of density functional theory (DFT) calculations of its vibrational circular dichroism (VCD) and optical rotation (OR) to the experimental VCD and OR of (+)−1, obtained in high enantiomeric excess using chiral gas chromatography. Conformational analysis of 1 demonstrates that the all-chair (CCCC) conformation is the lowest in energy and that other conformations are too high in energy to be significantly populated at room temperature. The B3PW91/TZ2P calculated IR spectrum of the CCCC conformation of 1 is in excellent agreement with the experimental IR spectrum, confirming the conformational analysis and demonstrating the excellent accuracy of the B3PW91 functional and the TZ2P basis set. The B3PW91/TZ2P calculated VCD spectrum of the CCCC conformation of S-1 is in excellent agreement with the experimental VCD spectrum of (+)−1, unambiguously defining the AC of 1 to be S(+)/R(−). The B3LYP/aug-cc-pVDZ calculated OR of S-1 over the range 589–365 nm has the same sign and dispersion as the experimental OR of (+)−1, further supporting the AC S(+)/R(−). Our results confirm the AC proposed earlier by Farina and Audisio. This study provides a further demonstration of the excellent accuracy of VCD spectra predicted using Stephens’ equation for vibrational rotational strengths together with the ab initio DFT methodology, and further documents the utility of VCD spectroscopy in determining the ACs of chiral molecules.
KeywordsAbsolute configuration Vibrational circular dichroism Optical rotation Perhydrotriphenylene
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