The low-lying triplet excited state of N-sulfinylanilines explains their reactivity and inclination to cycloaddition across N–S=O group

Abstract

Density functional theory calculations for p-Br-N-sulfinylaniline and m-nitro-N-sulfinylaniline in the ground singlet (S0) and triplet (T1) excited states are presented and analyzed in terms of their specific physicochemical properties. As all aromatic N-sulfinylamines, these compounds are rather unstable being sensitive to moist air and we assign this instability to the thermally allowed S0T1 excitation induced by internal magnetic forces. Our calculations indicate that the T1–S0 energy gap in these molecules is unexpectedly low and spin-orbit coupling matrix element between these states is relatively high, being allowed by the orbital symmetry selection rules. We also apply the exchange mechanism of spin-catalysis concept in order to explain the prone of N-sulfinylamines to the Diels-Alder cycloaddition with dienes.