A theoretical study of the structure, charge distribution and gas-phase basicity of 1-H-indazole and its N-methyl derivatives

Abstract

We have done ab initio calculations, using an STO-3G minimal basis set, for 1-H-indazole and its N-methyl derivatives, to illustrate that important structural differences exist between the two tautomers and that appreciable geometrical changes take place upon methyl substitution. Theoretical geometries, fully optimized at INDO level, are reported. The variations observed in the structures of the two tautomers are explained in terms of σ-valenceshell electron-pair repulsions and of changes in the π-densities of the HOMO'S of these compounds. It was also found that the tricoordinated nitrogen atom in 2-methylindazole (N2) is a much stronger π-donor center than N1 in the 1-methyl derivative, explaining some of the properties of these species. The calculated PA's indicate that these compounds are nitrogen bases and that the 2-methyl derivative is a much stronger base than the 1-methyl analog. Our calculated charge densities reproduce well the most important features of the 13C and 14 N NMR spectra of these molecules.