Nitrous oxide as a 1,3-dipole: A theoretical study of its cycloaddition mechanism

The 1,3-dipolar cycloadditions of nitrous oxide and substituted alkynes hav e been studied at the B3LYP/6-31G(d,p) level. The reaction is controlled by LUMO (dipole) - HOMO (dipolarofile) and involves aromatic transition struc tures. The shape of the potential energy surface and the regioselectivity a re not affected by the polarity of the solvents, except in the case of N2O + HC= CSiH3. Different reactivity criteria including FMO coefficients produ ct C, local softness differences A, magnetic susceptibility anisotropy chi (anis), and nucleus-independent chemical shifts NICS were used to predict t he regioselectivity in all studied cases; the C, A criteria turn out to giv e the best results among them. The aromaticity of the transition structure is not a factor in determining the regiochemistry of the cycloaddtition rea ctions.