CH acidity of five-membered nitrogen-containing heterocycles: DFT investigation

The CH acidity in gas phase and in THF and DMSO solution of 12 N-alkyl substituted azoles have been calculated with the density functional theory B3LYP method. The computed pK(a) values of azoles in THF solution and positions of deprotonation agree with experimentally found. The calculation results enabled us to explain a great difference in reactivity of 2-alkyltetrazoles comparing with 1-alkyltetrazoles in processes involving C-H bond cleavage (mercuration, iodination, aminomethylation). For studied compounds and corresponding anions three geometric aromaticity indices were calculated and pi-electron delocalization was studied by means of natural bond orbital analysis. The results obtained were used to explain positions of deprotonation of azoles' molecules. (C) 2009 Elsevier B.V. All rights reserved.