Kinetic isotope effect models as a function of ring substituent for indole-3-carboxylic acids and indolin-2-ones.

Abstract

The original strategic objective of my PhD researches in 1972-74 was to explore how primary kinetic hydrogen isotope effects might be influenced by the underlying structures of the transition states involved. Earlier posts dealt with how one can construct quantumchemical models of these transition states that fit the known properties of the reactions. Now, one can reverse the strategy by computing the expected variation with structure to see if anything interesting might emerge, and then if it does, open up the prospect of further exploration by experiment. Here I will use the base-catalysed enolisation of 1,3-dimethylindolin-2-ones and the decarboxylation of 3-indole carboxylates to explore this aspect. The systems and results are shown in the table below, summarised by the points: 1,3-DIMETHYL-INDOLINONES: 1 . The free energy barriers are very low, but show an overall increase when changing the substituent from nitro to amino, with the 6-position being more sensitive than the 5. However, the increase is not consistent. 2 . The transition state mode changes regularly, the wavenumber more than doubling along the