Experimental and Theoretical Quantitative Studies of the Hydrogen Bonding Basicity of 2,5-Disubstituted Tetrazoles...

The tetrazole cycle is a well-known pharmacophore fragment that is part of the structure of a large number of biologically active compounds, including drugs. The diverse biological properties of such heterocylic systems and related compounds are largely determined by their ability to form strong hydrogen bonds with the targets. However, quantitative data on the hydrogen bonding of such heterocycles are limited. In the present article, we have determined the hydrogen bonding basicity constants (pK_HB) of a series of 2-substituted-2H-tetrazoles as well as of some 1,5-disubstituted-1H-tetrazoles, 1H-triazoles in 1,1,2,2-tetrachloroethylene by means of FTIR spectroscopy. The influence of the nature of the substituents on the pK_HB values of these compounds has been evaluated. Also, the structure of the HB complexes and the theoretically predicted pK_HB values have been discussed by means of the DFT approach using the B3LYP/6-311++G(d,p) basis set and CPCM model. It was shown that in the case of 2,5-disubstituted-2H-tetrazoles, the endocyclic nitrogen atom at position 4 is the most preferred basicity center. Thermodynamic parameters of the hydrogen bonding complex formation have been also determined experimentally and calculated by the theoretical method.