KINETICS OF THERMAL RACEMIZATION OF (2S,3S)-1-C-13-1,2,3-D(3)-CYCLOPROPANE FOLLOWED BY VIBRATIONAL CIRCULAR-DICHROISM SPECTROSCOPY

Vibrational circular dichoism spectra recorded for (2S,3S)-1-C-13-1,2, 3-d(3)-cyclopropane and for mixtures of it and the three related stere oisomers prepared through gas-phase thermal stereomutation reactions a t 407 degrees C lead to the rate constant for racemization: k(alpha) = (4k(1) + 4k(12)) = (3.12 +/- 0.04) x 10(-5) s(-1). This and the rate constant measured for geometrical equilibration between the two chiral and the two achiral stereoisomers of 1-C-13-1,2,3-d(3)-cyclopropane, k(i) = (8k(1) + 4k(12)) = (4.63 +/- 0.20) x 10(-5) s(-1), give two equ ations in two unknowns, and allow one to solve for one-center (k(1)) a nd two-center (k(12)) epimerization rate constants for cyclopropane st ereomutations. They are nearly equal, a clear indication of closely co mpetitive reaction pathways.