Hydrogen exchange in phenylacetylene and the hydroxide ion anomaly

Abstract

The general base-catalysed exchange of acetylenic hydrogen in phenylacetylene is found to give a Brønsted correlation with unit slope and no primary isotope effect, indicating that a diffusion or rotation step following proton transfer is the rate-determining stage of this reaction; comparison of this result with the behaviour of chloroform suggests an explanation for the substantial deviations generally shown by hydronium and hydroxide ions from Brønsted plots for proton transfer to or from carbon based on other catalysts.