Nucleophilic reactivity towards ‘normal’ and ambidentate electrophiles bearing the nitroso group

Abstract

Bimolecular rate constants for the reactions of N-methyl-N-nitrosotoluene-p-sulfonamide (MNTS) and 2-ethoxyethyl nitrite (EEN) with oxygen nucleophiles [HO^–, CF₃CH₂O^–, HO₂^–, CH₃(CO)NHO^– and ClO^–], sulfur nucleophiles (SO₃^2–, SCN^–, thiourea, cysteine, S₂O₃^2– and HS^–) and I^– have been determined. For MNTS, ‘soft’ nucleophiles react at the nitroso group, whereas ‘hard’ nucleophiles react at least in part at the sulfonyl group. A discussion on the validity of nucleophilicity scales (N₊ and n) is carried out and clearly for soft nucleophiles (N- and S-nucleophiles and I^–) there is a good correlation with N₊ with a slope close to 1 which implies a frontier orbital controlled reaction and a markedly diradicaloid transition state. For reactions at the sulfonyl group (O-nucleophiles), nucleophilic reactivity is better explained using the n scale which can be rationalized in terms of a larger electrostatic contribution to the interaction energy.