Optical Activity due to Isotopic Substitution. Vibrational Circular Dichroism and the Absolute Configurations of α-Deuterated Cyclohexanones

Article abstract of DOI:10.1021/ja00408a012

The first syntheses of optically active cyclohexanone (1) and <2-3H>cyclohexanone (2) are presented.These compounds are synthesized by use of the enzyme acetoacetate decarboxylase (AAD), and assignments of configurations based on chemical degradation and spectroscopy are described.Circular dichroism spectra for electronic transitions and fundamental vibrational transitions are reported for both enantiomers of 1 from 2000 to 40 000 cm^-1.The results of observation and calculation of vibrational circular dichroism (VCD) intensities of 1 and its α-monodeuterio analogue, 3, are presented in both the C-H and C-D stretching regions.Qualitative agreement is obtained between experiment and theory in the C-H region of 1, confirming the results of independent determinations of absolute configurations.Measurable VCD in the C-H stretching region was not observed for dilute solutions of either enantiomer of 3 in cyclohexanone-CCl4 although strong VCD bands were observed in the C-D stretching regions of both enantiomers.Only minimal VCD is predicted in the C-D stretching regions of 1 and 3; however, large observed intensities over a wide frequency range in this region indicate a pronounced and possibly obscuring contribution from overtone and combination bands.The utility of enzymic methods for synthesis of chirally deuterated molecules is described, along with the potential for assignment of absolute configuration by VCD compared with chemical degradation.