| Abstract
| - The three isomeric methylpyridines and the three isomeric cyanopyridines each constitute a photochemicaltriad. Irradition of each methylpyridine or each cyanopyridine in the vapor phase at 254 nm results in theformation of the other two isomers as primary photoproducts. Dideuteration of the 2-substituted or3-substituted methyl or cyanopyridines expanded each triad to a pentad. Due to symmetry, 2,6-dideuterationof 4-methyl-or 4-cyanopyridine did not expand the triad. Trideuteration of 4-methylpyridine removedthis symmetry and resulted in a photochemical pentad. These results are consistent with a mechanisminvolving 2,6-photocylization, migration of nitrogen around the five sides of the cyclopentenyl ring, andrearomatization. This mechanism exactly predicts the observed distribution of deuterium in thephotoproducts.
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