On the structure and energies of protonated cations of H₂CS, HFCS, and F₂CS

Abstract

Using 4-31G basis sets, the geometries of H2CS, HFCS, and F2CS as well as their protonated cations were optimized. In each case, three protonation sites, S, C, and H (for H2CS) or F (for HFCS and F2CS) were considered. The H or F protonation leads to molecular complexes of the form HX … YCS+. For H2CS and F2CS, the S-protonation site is favored, whereas for HFCS the linear complex HF … HCS+ is the most stable protonated form. Predicted proton affinities are 177.4 for H2CS (180.9 experimental), 172.0 for HFCS, and 149.1 kcal/mol for F2CS.

Thiouracils: Acidity, Basicity, and Interaction with Water

“…Furthermore, the substitution of O by S in 2TU and 4TU does not significantly affect the PA(B) value of the other O atom, which is nearly the same as for uracil. As demonstrated in other works, [60][61][62][63][64] thiocarbonyl derivatives are considerably more basic than their carbonyl homologues. In the present case, the PA(B) value of the S2 atom is 23-26 kJ mol -1 larger than that of the O2 atom, and the PA(B) value of the S4 atom is 13-20 kJ mol -1 larger than that of the O4 atom.…”