Crystal structure of long alkyl 3-(thymin-1-yl)propionates: Style of hydrogen bonding and dependence on the alkyl chain length

Crystal structures of the ester derivatives of thymine having long alkyl chains are described. The crystal structure of the thymine derivative was found to be affected particularly by the carbon number of the alkyl chain. The thymine derivatives having even-numbered alkyl chains formed unusual hydrogen bonds between N3-H and O2 of the thymine base. The interactions between the methyl group and the oxygen were found to play an important role in the crystal structure. The thymine base of the even-numbered alkyl derivatives was surrounded by neighboring molecules with the interactions between the methyl group and the oxygen. Therefore, usual hydrogen bonds between N3-H and O4 were inhibited by steric effects from forming the hydrogen bonds between N3-H and O2.