Local spin III: Wave function analysis along a reaction coordinate, H atom abstraction, and addition processes of benzyne

The recently derived local spin operator directly determines the spin state of an atom or molecular fragment A, whereas the <(SASB)-S-.> operator represents the Heisenberg Hamiltonian spin coupling between A and B. Although one typically associates such spin properties with open-shell molecules, in the singledeterminant molecular orbital approximation, these operators may be related to chemically relevant quantities such as bond order reaardless of whether the system has impaired electrons. Here we demonstrate the usefulness of these operators as molecular properties that can be applied to wave functions for which many properties are not defined, namely, multi determinant wave functions. Analysis of the wave functions of o-, m-, and p-benzyne indicates that these spin operators are able to detect subtle differences in electronic structure within a series of isomers with unpaired electrons. Hydrogen atom addition and abstraction processes are then used to illustrate that the operators are able to track changes in a wave function along a reaction coordinate and to obtain chemically relevant information about the development of radical character on an atom and the extent of spin coupling between atoms that are involved in bond formation.