A semiempirical investigation of identity-reaction proton transfers using the AMI and PM3 methods has been carried out. Enthalpy differences between separated reactants and the ion-dipole complex (well depth) and between the complex and the transition structure (barrier height) were calculated. A comparison of carbon-to-carbon and oxygen-to-oxygen proton transfers led to the unexpected result that barriers were higher for the latter than for the former, in contrast to experimental observations in solution. The calculated values are compared with experiment and with ab initio calculations where possible, and the reliability of semiempirical calculations of well depths and barrier heights is assessed
