Photochemical deuterium exchange

A quinone methide makes a surprising appearance as an intermediate of the photochemical exchange of deuterium from D20 into the 2 -position of 2-phenylphenol (13).27 29 No photochemical deuterium exchange is observed for reactions of the related phenylanisole 10 or phenylphenols 11 and 12, and deuterium exchange at the 4 -phenyl position of 13 is very much slower than... 

Electrophilic deuterium exchange reaction is also photosensitized. Thermal and photochemical processes show a different orientation of deuterium exchange. 

Mason and Smith (1969) found that for a series of mono- and bicyclic aromatic hydrocarbons the changes in the fluorescence spectrum with acidity reflected the ground state protonation reaction. The p Sj )-values calculated for benzene, toluene, naphthalene, azulene, and indolizine do not correspond to observable processes since the rate of protonation is too slow to compete with deactivation of the Sj state. Photochemical deuterium and tritium exchange experiments in 1 mole dm-3 perchloric acid indicate that the radiative deactivation rate of an electronically excited aromatic hydrocarbon is faster than the rate of protonation by a factor >10s. 

Studies of the photochemical formation of benzyl carbanions have been reported for two systems this year. Ultra-violet light irradiation of (420) in aqueous acetonitrile resulted in formation of (421) exchange of the benzylic hydrogens of (420) was also observed when heavy water was used in the solvent. Compound (421) was shown to arise by two pathways a di-7r-methane rearrangement, and a 1,7-hydrogen shift followed by electrocyclic closure. The deuterium exchange reaction is presumed to occur due to... 

Aromatic compounds similarly undergo photoprotonation, as evidenced by their fluorescence quenching in acidic media, acid-catalyzed ipso photosubstitution of alkoxy benzenes, and photochemical deuterium exchange of aromatic ring protons [100,101]. McClelland has summarized in a recent review the observation of transient spectra from cyclohexadienyl cations upon laser flash photolysis of several aromatic compounds in HFIP [5,98,102-105]. 

For example, we can easily tell how to make a forbidden reaction in the ground state, allowed photochemically. Consider a simple reaction, hydrogen deuterium exchange... 

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