Electrophilic hydrogen‐deuterium exchange of some deactivated pyrroles

Abstract

AbstractThe rate coefficients and partial rate factors for the hydrogen‐deuterium exchange of some 1‐substituted pyrroles (1‐substituents = ‐COCH3, ‐ COC6H5, ‐SO2CH3, ‐SO2CF3, ‐N(CH3)3, ‐NH(CH3)2, ‐SO2C6H5) in deuterated trifluoroacetic acid have been determined. In all cases the rate of exchange is faster at the 2‐position. Similarly, the hydrogen‐deuterium exchange of some pyrroles with electron withdrawing substituents in the 2‐position indicate a relative reactivity of 4→ 5→ 3‐position with the selectivity being greatest for the more electron withdrawing groups. A nitro group in the 3‐position of pyrrole shows a relative reactivity of 5→2→4‐position for the hydrogen‐deuterium exchange in deuterated trifluoroacetic acid. A linear correlation is observed for the log of the rate coefficient of the hydrogen‐deuterium exchange at the 4‐position of some 2‐substituted pyrroles and the difference in the calculated energy of formation of the pyrrole and the corresponding 4‐deuterated cation.