Hydrogen bonding between adenine and 2,4-difluorotoluene is definitely not present, as shown by concentration-dependent NMR studies

The chloroform-soluble nucleobase derivatives N-9-cyclohexylmethyladenine (A) and N-1-cyclohexylmethylthymine (T) have been synthesized in order to study hydrogen-bonding interactions between A and the thymidine mimic 2,4-difluorotoluene (F) in CDCl3 at high concentrations. Concentration-dependent H-1 NMR experiments show that in the presence of F, A undergoes self-association rather than pairing with F. These results strongly support the assumptions made by Kool with regard to the lack of hydrogen bonding between adenine and 2,4-difluorotoluene.(3).