| We calculated the singlet-triplet energy splittings for several carbene and nitrenium ion molecular systems. Carbenes and nitrenium ions are single-centered diradicals which incorporate a divalent carbon atom and nitrogen cation respectively. Since they have two nonbonding electrons, they can adopt either a singlet or triplet spin multiplicity, each having different lifetimes and reactivities. Since carbenes are ubiquitous in organic synthesis and nitrenium ions are implicated as carcinogenic agents, understanding of the structural factors which influence the stability of a given spin multiplicity was the goal of this study.;We employed several ab initio computational chemistry methods to characterize the singlet and triplet electronic structures and to determine the singlet-triplet energy splittings for several substituted carbenes and nitrenium ions. Among the methods were Hartree-Fock Self-Consistent Field, Multi-Configuration Self-Consistent Field, and Density Functional Theory methods. The former two methods are well-established while the latter method is relatively new. We calibrated the performance of Density Functional Theory methods for predicting the singlet-triplet energy splittings of the diradicals studied against the established methods since Density Functional Theory may be able to treat larger molecular systems than can currently be treated with the standard molecular orbital methods. |
