1-Naphthaldehyde, photoreduction

To test this hypothesis, a-naphthaldehyde, which is apparently inert toward photoreduction, was irradiated in the presence of optically active 2-octanol. If a reversible hydrogen abstraction were to occur, a loss of optical activity in the 2-octanol should result. The results showed no loss in optical activity thus the question of a reversible reaction has been answered/33 ... 

The photoreductions of a number of carbonyl compounds with either lowest mr or jiji triplet states in the presence of tributyltinhydride are reported24. The carbonyl compounds include cyclohexanone and acetone which possess nrr lowest-energy triplets, and 2-acetonaphthone, 1-naphthaldehyde and 2-naphthaldehyde which possess lowest-energy mr triplets. In the case of the two njr triplets, a simple mechanism is proposed which involves the abstraction of a hydrogen atom from the tributyltinhydride by the triplet state... 

Reluctance to photoreduction shown by 1-naphthaldehyde has also been attributed to lack of reactivity of the lowest (7t,7i )-triplet state... 

Quantum yields for photoreduction of 1-naphthaldehyde, 2-acetonaphthone,370 and p-phenylbenzophenone365,366 in 2-propanol are all 0.1 or lower, as compared with a limiting value of 2 for benzo-phenone. Since the triplets of the first three compounds undoubtedly possess a 77,77 configuration366,370 and a hundredfold longer lifetime... 

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