STEREOCHEMISTRY OF THE THERMAL-CONVERSION OF 1-VINYL-2,3-CIS-DIDEUTERIOCYCLOBUTANE TO BUTADIENE AND 1,2-DIDEUTERIOETHYLENES

This study has examined the stereochemistry of the decomposition at 90 0-1000 K in a single-pulse shock tube of 1-vinyl-2,3-cis-dideuteriocyc lobutane to ethylenes and buta-1,3-dienes. The deuterated ethylenes fo rmed during the decomposition, CHD-CH2, (E)-CHD=CHD, and (Z)-CHD=CHD, were quantified via two independent techniques, FTIR and IR absorption spectroscopy using a tunable diode laser spectrometer. The results of both analyses indicated that equal amounts of (E)-CHD=CHD and (Z)-CHD =CHD were formed from the cis-labeled reactant. In an earlier shock tu be study of the decomposition at 1000-1200 K of two deuterium-labeled cyclohexenes to ethylenes plus buta-1,3-dienes, a pathway via a vinylc yclobutane intermediate was implicated in a significant fraction of th e decomposition events; the measured ratios of (E)-CHD=CHD to (Z)-CHD= CHD in that study were consistent with a complex mechanistic model in which the stereochemistry of deuterium labels in the cyclohexene react ant was lost in ethylene products formed via vinylcyclobutane. The pre sent results provide additional support for that model.