Heteroaromatic hydrogen exchange reactions. Part V. Isotope effects for the acid-catalysed exchange of 3-3H1-2-methylindole and 3-2H1-2-methylindole

Abstract

Hydrogen exchange rates are reported for 2-methylindoles labelled with either deuterium or tritium at the 3-position in a range of acetic acid buffer solutions at 25 °C prepared in either H₂O or D₂O. Various isotopic rate ratios calculated from these data are entirely consistent with an A–S_E2 mechanism for the hydrogen exchange, in which the proton is approximately half-transferred to the substrate in the transition state.