Classification of reaction pathways via momentum–space and quantum molecular similarity measures

For four rearrangement reactions, we evaluate (i) values of the moments of momentum 〈pn〉(−2⩽n⩽+1) for reactants, products and transition states (ii) position–space similarity indices between reactants, products and transition states using wavefunctions generated from both Hartree–Fock and density-functional theory (B3LYP). Both the momentum–space expectation values and the similarity measures can be used to distinguish Hammond and anti-Hammond behaviour. In position–space, two new parameters, δ and φ, are introduced to quantify the position and character of the transition state relative to the reactants and products.