Structures and photodimerizations of 1-alkylthymine crystals obtained fromN,N-dimethylformamide

Single crystals of I-alkylthymine (carbon numbers of the alkyl chain were 8 , 11, 12, 13, 14, and 16) were obtained from N,N-dimethylformamide (DMF) so lution as plates, and the crystal structures were determined by X-ray cryst al analysis. The terminal methyl group of the alkyl chain was found to appr oach to the double bond of the thymine base in the crystal. The thymine bas es in these crystals did not give the photodimer by UV irradiation, while t he crystals obtained from ethyl acetate and acetonitrile gave the photodime r as reported previously. The terminal methyl group of the alkyl chain was concluded to inhibit the relation of the thymine bases in crystal, which ma de the crystal from DMF inactive for the photodimerization.