NUCLEOPHILIC REACTIVITY TOWARDS NORMAL AND AMBIDENTATE ELECTROPHILES BEARING THE NITROSO GROUP

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.