ROLE OF FRONTIER MOLECULAR ORBITAL ENERGIES IN [3+2]-CYCLIZATION OF NITRILE OXIDE TO ACETONITRILE
The reaction [3 + 2] of cycloaddition of nitrile oxide, the product of the intramolecular transformation of a substituted aromatic nitrosooxide, to acetonitrile was studied using quantum chemical methods. The main stationary points of the chemical trajectory are localized in the approximation of hybrid M06L functional with triple split valence basis set [6-311 + G (d, p)]. It was found that groups possessing electron-withdrawing (-CN, -NO2), as well as electron-donating (-OMe, NMe2) properties and located in β/dand α/γ/e-positions, respectively, contribute to a relative decrease in the activation enthalpy of the reaction. The topology and energy of the highest occupied and the lowest unoccupied molecular orbitals (MO) of nitrile oxide and acetonitrile are analyzed using the Sustman classification. The role of an electron donor uncharacteristic for acetonitrile in the cyclization reaction was established on the base of frontier molecular orbital (FMO) formalism: it was shown that the effectiveness of nitrile oxide as an electron density acceptor does not depend on the position and nature of the substituents included in it, and it is most likely due to the action of the terminal oxygen atom localized in the region of the active part of the molecule for the reaction.