Theoretical prediction of proton and electron affinities, gas phase basicities, and ionization energies of sulfinamides

Abstract

Sulfinamides, as an asymmetric synthesizer, especially in drug synthesis, play critical roles in organic chemistry. In this study, the gas phase ion energetics data including the topical proton affinities, topical gas phase basicities, adiabatic and vertical ionization energies (IE), and electron affinities of sulfinamides were calculated at B3LYP/6-311++G(d,p), G4MP2, and MP2/6-311++G(d,p) levels. Determination of the actual protonation sites of sulfinamides is an important challenging issue in the experimental investigations. Three significant centers, including oxygen atom, sulfur atom, and nitrogen atom of the amide functional group of the sulfinamides, can be protonated. Our calculations indicate that in most cases, oxygen center is the most probable protonation site of sulfinamides. Bond polarities and bond lengths of ionic species in comparison with the corresponding neutral molecules are investigated. The effect of these parameters on the calculated topical proton affinity and topical gas phase basicity values is discussed. The energy barriers for internal proton transfer of different sites in protonated sulfinamides were obtained and discussed at MP2/6-311++G(d,p) level of theory. Results show the IEs increase when the electron acceptor substituents are connected to the S—O group, while the electron donor functional groups reduce the IE values. The EAs were shifted to more positive values if the H atom of sulfinamide substitutes with an electron acceptor functional groups.