Benzpinacol, from benzhydrol

We saw earlier that when benzophenone is photoreduced in the presence of optically active 2-butanol, the alcohol recovered from the reaction loses no optical activity/541 This was presented as evidence that there could be no appreciable reversibility of the initial hydrogen abstraction since this should lead to racemization of the unreacted alcohol. However, if one uses relabeled benzhydrol and examines the initially produced benzpinacol for the presence of the label, one finds that the product pinacol contains no 14C. This would indicate that there must be some type of rapid transfer of the hydrogen radical from the ketyl radical produced upon abstraction from benzhydrol,... 

Category 5. Hydrogen Atom Abstraction. When benzophenone is irradiated in isopropyl alcohol, the initially formed Si state crosses to the Ti state, which abstracts hydrogen from the solvent to give the radical 7. Radical 7 then abstracts another hydrogen to give benzhydrol (8) or dimerizes to benzpinacol (9) ... 

Exists in stable and labile modifications Stable form rhombic prisms, m.p. 49° B.p 306°. Sol. EtOH, EtgO, AoOH, Insol. HgO 1 0976. Labile form monoclinio prisms, m.p. 26°. Sunlight — benzpinacol. Na -1-EtOH — diphe lmethane. NaHg —> benzhydrol. Zn + HgSOg —> benzpinacol —> a-benzpinaoolin — -benzpinaoolin, Di-Meacetal plates from Et 0. M.p. 106-7° B.p. 288-90°. 

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