Abstract
Reaction was induced between trans-2-butene and nitrogen dioxide by exciting trans-2-butene-NO{sub 2} pairs, isolated in solid Ar at red, yellow, and green wavelengths (NO{sub 2}{sup 2}B{sub 2} {l arrow} {anti X}{sup 2}A{sub 1}). The chemistry was monitored by FT-infrared spectroscopy, and Ar ion and cw dye lasers were used for photolysis. Products formed were 2-butene oxide + NO, the former under complete retention of stereochemistry, and an addition product that was identified by {sup 18}O isotopic substitution as a butyl nitrite radical, reported here for the first time. Analysis of the photolysis-wavelength dependence of the butyl nitrite radical and trans-2-butene oxide (NO) growth kinetics revealed that epoxide + NO is formed along two reaction pathways. The first gives trans-2-butene oxide + NO and butyl nitrite radical upon absorption of a single photon by trans-2-butene-NO{sub 2} pairs (one-photon path). The second path is formation of trans-2-butene oxide + NO by photodissociation of trapped butyl nitrite radical by a (second) red or shorter wavelength photon (two-photon path). Two alternative transients are proposed for the one-photon path, namely a hot butyl nitrite radical and an oxirane biradical, respectively. The wavelength dependence of the product branching along the one-photon path indicates that branching occursmore » from a vibrationally unrelaxed transient. This suggests that the observed stereochemical integrity originates from insufficient coupling of the stretching and bending vibrations of the transient with torsion around its central C-C bond on the time scale of reaction to epoxide + NO and its stabilization as butyl nitrite radical.« less
Published Version
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