An improved procedure using vibrational circular dichroism spectroscopy for high-precision determinations of enantiomeric excess (ee) in chiral samples is described. Chiral trans-dideuteriocyclopropane is employed in the gas phase for percent ee measurements. This molecule is a member of the class of simple hydrocarbons made chiral by virtue of isotopic substitution for which no convenient and accurate alternative method of percent ee measurement is available. Percent ee determinations to within 1% are demonstrated for several ee values with and without contamination by the achiral cis-dideuteriocyclopropane species.
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