2-alkyl-5-aryltetrazoles as hydrogen bond acceptors

The dissociation constants of the H-complexes formed by 2-alkyl-5-aryltetrazoles and p-fluorophenol in carbon tetrachloride (pK _HB 0.9–1.3) were determined by Fourier-transform IR spectroscopy. 2-Alkyl-5-aryltetrazoles were found to act as medium-strength hydrogen bond acceptors comparable with diazines. The thermodynamic parameters of the equilibrium formation of H-complex with 2-isopropyl-5-phenyltetrazole were determined. The electronic nature of substituents in the tetrazole ring only slightly affects the pK _HB values of tetrazoles.