The kinetics and mechanism of the electrophilic substitution of heteroaromatic compounds. Part XXXIV. The hydrogen-exchange rates of methylpyrazoles

Abstract

Acid-catalysed hydrogen-exchange rates are recorded for 1-methylpyrazole and for its 3-, 4-, and 5-mono- and 3,4-, 3,5-, and 4,5-dimethyl derivatives, together with those for the corresponding 2-methylpyrazolium cations. The rates have been extrapolated to give rate constants at 100° and pH 0: these are discussed with reference to the effect of the methyl groups and of the two cyclic pyrazole nitrogen atoms on electrophilic substitution rates.