The interaction of didodecylbarbituric acid with 9-hexadecyladenine or 1-hexadecylthymine through molecular recognition of their complementary moieties is investigated in aprotic solvents and in the bulk. In solution, complex formation was established by NMR spectroscopy while their association constants were determined in heptane by UV spectroscopy at low concentrations in contrast to the determination with NMR or infrared spectroscopy which requires higher concentrations. Intermolecular hydrogen bonding complexation was investigated in the bulk phase, by FT-IR spectroscopy, as a function of the temperature. Due to the bulkiness of the adenine derivative, 1:1 complexation occurs with barbituric acid derivative although the latter possesses two binding sites. The complex formed is stable within a broad temperature range, viz., from room temperature to the second endothermic transition, associated with the complete melting of the interacting mixture. Thymine derivative, on the contrary, forms with alkylated barbituric acid both 1:1 and 1:2 hydrogen-bonded complexes which are stable even at temperatures exceeding second phase transition attributed again to the completion of the sample melting.