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 (SO32–, SCN–, thiourea, cysteine, S2O32– 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.