Competing sigmatropic shift rearrangements in excited allyl radicals.
The competition between rearrangement of the excited allyl radical via a 1,3 sigmatropic shift versus sequential 1,2 shifts has been observed and characterized using isotopic substitution, laser excitation, and molecular beam techniques. Both rearrangements produce a 1-propenyl radical that subsequently dissociates to methyl plus acetylene. The 1,3 shift and 1,2 shift mechanisms are equally probable for CH(2)CHCH(2), whereas the 1,3 shift is favored by a factor of 1.6 in CH(2)CDCH(2). The translational energy distributions for the methyl and acetylene products of these two mechanisms are substantially different. Both of these allyl dissociation channels are minor pathways compared to hydrogen atom loss.
Stranges
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Dipartimento di Chimica, Università La Sapienza, Rome, Italy. domenico.stranges@uniroma1.it
O'Keeffe
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Scotti
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Di Santo
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Houston
P L
PL
D000498:Allyl Compounds / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D003198:Computer Simulation; D005609:Free Radicals / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation
D000498:Allyl Compounds; D005609:Free Radicals; D002244:Carbon; D006859:Hydrogen