Gas-phase properties and Fukui indices of sulfine (CH2SO). Potential energy surface and maximum hardness principle for its protonation process. A density functional study

Gas-phase thermochemical properties of sulfine (CH2SO) and the potential en ergy surface of its protonation process were studied by the density functio nal method employing different exchange-correlation potentials. All calcula tions showed that the most stable protonated isomer is planar with the prot on bonded to the oxygen atom in a trans arrangement of the skeleton. Three transition slates were located that allow interconversion between the diffe rent isomers. Hardnesses and Fukui indices were calculated to follow the re activity trend along the protonation path and to explain the preference for a particular protonation site on neutral sulfine. Proton affinity, gas-pha se basicity and heat of formation values, obtained for the first time fully quantum mechanically, agree well with those derived by a recent mass spect rometry experimental study. Good agreement between density functional theor y and previous high-level theoretical and experimental data was also found for the heat of formation of sulfine and its most stable protonated form.