DFT and G4MP2 calculation of proton and electron affinities gas phase basicities and ionization ener gies of sulfinamides

Sulfinamides, R1SONR2, (also known as amino hydrogen sulfoxides), are important chiralbuilding blocks in organic synthesis. Oxidation of sulfinamides using singlet oxygen yieldssulfonamides, which have a wide variety of applications in medicinal chemistry [1]. Protontransfer reactions and ionization processes play a key role in the chemistry and biochemistry.Proton affinity (PA) and gas phase basicity (GB) determine the capability of an atom a moleculeto accept a proton in the gas phase. Ionization energy (IE) is the quantity of energy that a gaseousmolecule in the ground electronic state must absorb to lose its electron, resulting in a cation.Electron affinity (EA) can reflect the ability of an atom to gain electron [2].In this study, the topical PA and GB as well as IE and EA of a set of sulfinamides includingsulfinicamide, methanesulfinamide, benzenesulfinamide, trifluoromethanesulfinamide, Nmethyelsulfinamide, N,N-dimethyl methanesulfinamide, 1,1,1trifluoroN-methyelmethanesulfinamide, 1,1,1trifluoro N,N-dimethyl methanesulfinamide were calculated andcompared using B3LYP/6-311++G(d,p) and G4MP2 methods. Sulfinamides have two suitablesites, oxygen and nitrogen atoms, to accept a proton. Hence, it was calculated two differentvalues for the PA and GB of each molecule. The calculated PA and GB of sulfinamides forprotonation of the oxygen site is higher than that of the nitrogen site in both levels of theory. Inoverall, the values of PA and GB at the B3LYP computational level was more than that ofG4MP2. Electron donor substituents at the SO group increases PA and GPB of sulfinamideswhereas electron acceptor substituents decreases PA and GPB of sulfinamides for protonation ofboth nitrogen and oxygen sites. The proton affinity of R1SONH2 (R1: Ph, Me, H, CF3) werecalculated as, 904, 875, 853, 814 kJ/mol, respectively, for R1SONHMe (R1: Me, CF3) were909.2 and 836 kJ/mol and for R1SONMe2 (R1: Me, CF3) were 922 and 852 kJ/mol, all valueswere obtaind from B3LYP method at 298 K and for protonation of oxygen site. Calculatedadiabatic and vertical IEs were in the range of 8.05-10.14 eV. The results show that the VIEvalues are more than the AIE. As an example, the AIE of trifluoromethanesulfinamide andbenzenesulfinamide calculated at the B3LYP level were 9.58 and 8.51 eV, respectively, whiletheir VIE were 10.14 and 8.87eV, respectively. The calculated AIE of trifluoromethanesulfinamide and benzenesulfinamide at the G4MP2 level were 9.65 and 8.85 eV,respectively. In the same manner, the calculated VEA values were positive than AEA values.

Keywords:

sulfinamides , proton affinity , gas phase basicity , electron affinity , ionization energy References