Hydrogen Donating Solvent Participation in the Photochemistry of Benzaldehyde and Deoxybenzoin: A 13C CIDNP Study
Photolysis of Benzaldehyde (1; 90percent (13)C=O) in cyclohexane-d12 results in the formation of benzaldehyde-h and -d with emissive CIDNP for the (13)C=O function.This observation requires a secondary encounter of the free benzoyl radical with either phenylhydroxymethyl or cyclohexyl-d11 radicals.Photolysis of deoxybenzoin (5; 99percent (13)C=O) and p-chloro-5 (99percent (13)C=O) in cyclohexane-d12 also generates benzaldehyde-h and -d with the same emissive CIDNP for the (13)C=O function.These observations are rationalized in terms of previously unreported primary intermolecular deuterium abstraction by photoexcited deoxybenzoin from the (deuterated) solvent.This assignment is supported by the significantly decreased measured lifetime of triplet deoxybenzoin in cyclohexane-h and -d (429 and 724 ns, respectively) compared to the lifetime in benzene (847 ns).
Mechanistic aspects of the C-H alkynylation reaction of acetylenic triflones. Determination of phenyl versus cyclohexyl migratory aptitude for a vinylidine carbene
13C-2 labeled phenyl ethynyl triflone undergoes regiospecific C-H alkynylation upon reaction with cyclohexane. The 13C label is found to be exclusively adjacent to the phenyl group in the product phenyl cyclohexyl acetylene, consistent with cyclohexyl radical addition at the α-position. Control studies show preferential phenyl migration from a vinylidine carbene, thus excluding the presence of such an intermediate.
Xiang, Jason S.,Fuchs
p. 5269 - 5272
(2007/10/03)
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