A theoretical investigation on the cycloaddition reaction between azocarbenium ions and nitriles.

The 1,3-dipolar cycloaddition reactions of the cationic 1,3-dipolarophiles of azocarbenium ion 1 with HCN in the gas phase were examined using the density functional theory, QCISD method (Quadratic configuration interaction using single and double substitutions) and CCSD(T) (Coupled cluster calculations with single and double excitations and a perturbative estimate of triple contributions calculations) calculations. The theoretical results revealed that the reaction takes place via an initial formation of a 1:1 complex of the two reactants, mainly driven by charge interaction, followed by an asynchronous concerted cyclization forming the 3H-[1,2,4]-triazolium ion 3, which undergo [1,2]-H shift to provide the 1H-[1,2,4]-triazolium ion 4. The effect of the solvent has been modeled by using the isodensity-surface polarizable continuum (IPCM) model and the calculation showed that the reaction in CH₂Cl₂ solution proceeds in a similar manner as in gas phase with only a slight derivation of activation barrier. The substituent effects have also been investigated. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]