Intramolecular Photochemical Hydrogen Abstraction in 2-Alkylpyrazines and 2-Alkylpyridines

Article abstract of DOI:10.1021/jo00080a029

Photochemical hydrogen abstraction in 2-alkylpyrazines 5-8 and 2-alkylpyridines 9-11 proceeds analogously to the process of eq 1.Hydroxylic solvent causes quantum yields for pyrazine fragmentation products (Φ_p) to increase about 1 order of magnitude.Pyridine fragmentation takes place from both singlet and triplet states.Pyrazine fragmentations follow Stern-Volmer kinetics with modest bond strength selectivity (1 deg : 3 deg ca. 1:17 for 5a and 5c).Methyl substitution lowers the rate of abstraction in pyrazines and trifluoromethyl substitution increases Φ_p in pyridines.It is suggested that these effects reflect changes in the n?^* and ??^* character of the reactive excited states.