Hydrogen stretching vibrational circular dichroism in methyl lactate and related molecules

Denise M.P. Gigante, Fujin Long, Louise A. Bodack, Jeffrey M. Evans, James Kallmerten, Laurence A. Nafie, Teresa B. Freedman

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Abstract

The CH- and OH-stretching vibrational circular dichroism (VCD) spectra of methyl lactate and related molecules in CCl4 solution have been investigated to identify solution conformations and establish a correlation between OH- and methine-stretching VCD intensity and molecular structure. Deuterium substitution was used when possible to remove overlapping absorption features in the CH-stretching region. Anisotropy ratios between +2.1 × 104 and +2.8 × 104 were measured for the methine-stretching VCD of the molecules with both α-oxy and α-C=O substituents: (S)-methyl-d3 lactate, (S)-methyl-d3 2-(methoxy-d3)-propionate, di(methyl- d3) D-tartrate, (S)-methyl-d3 mandelate, (S)-methyl-d3 O-(acetyl-d3)-mandelate, and (S)-benzoin. The methine- stretching VCD intensity serves as a marker for both absolute configuration and solution conformation in these molecules, as previously demonstrated for amino acids and peptides. In (S)-methyl 2-chloropropionate, (R)-methyl 3-hydroxy-2-methylpropionate, and (S)-methyl 3-hydroxybutyrate, the net CH-stretching VCD intensity is small relative to that in the other molecules studied. Ab initio calculations of geometries, vibrational frequencies, and unpolarized infrared absorption (IR) and VCD intensities were carried out to identify the most abundant solution conformers from the VCD spectra and to correlate OH- and methine-stretching VCD intensity with molecular conformations. Factors leading to large methine-stretching VCD anisotropy ratios are assessed.

Original languageEnglish (US)
Pages (from-to)1523-1537
Number of pages15
JournalJournal of Physical Chemistry A
Volume103
Issue number11
DOIs
StatePublished - Mar 18 1999

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Gigante, D. M. P., Long, F., Bodack, L. A., Evans, J. M., Kallmerten, J., Nafie, L. A., & Freedman, T. B. (1999). Hydrogen stretching vibrational circular dichroism in methyl lactate and related molecules. Journal of Physical Chemistry A, 103(11), 1523-1537. https://doi.org/10.1021/jp9837885