Abstract

N-sulfinyl compounds RNSO show a wide range of reactivities to water with a change of the substituent R. For several N-sulfinylamines, Mironova and Konoplva proposed that the reaction of a pyridine-H 2 O complex with the N-sulfinylamine is the rate-determining step in its hydrolysis. And later, Cerioni et al. observed complexes of N-sulfinylamines with pyridine by 13 C and 17 O NMR spectroscopies and proposed an equilibrium between "free" and "complexed" N-sulfinylamines. Muchall proposed an anti-hydrogen bond, C-H...0, in N-sulfinylamines through an analysis of the calculated electron density. We are interested in whether the C-H...O interaction has an effect on the reactivity of the sulfur atom in RNSO compounds, especially in N-sulfinylanilines. Using 1 H and 17 O NMR spectroscopies we have obtained experimental evidence for the C-H...O interaction. The 17 O chemical shifts are more sensitive to the polarity or polarizability of a solvent rather than to its H-bonding capabilities, which support the fact that the oxygen atom is involved in an intramolecular C--H...O interaction. The small dependence of the 17 O chemical shift of all N-sulfinylanilines on the H-donating ability of a solvent supports the idea of planar molecules with intramolecular C--H...O bonds. The strength of the C--H...O interaction is dependent on the strength of the S...N interaction in the complexes of N-sulfinylanilines with pyridine. Temperature studies show an increasingly deshielded (shielded) 17 O ( 1 H) nucleus upon an increase in temperature, and ortho 1 H nuclei are deshielded as the pyridine concentration is increased. These changes can be interpreted to demonstrate a strengthening of the C--H...O interaction upon S...N complexation. Equilibrium constants show that an electron donating substituent leads to a weaker complex. It is also shown that a weaker complex possesses a stronger C--H...0 interaction based on substituent effects on the temperature dependence of the 17 O nucleus in a complex. It is deduced that a "strong" C--H...0 interaction could inhibit complexation, and maybe lead to a reduced reactivity of a N-sulfinylaniline.