Rates of detritiation of phenylacetylene-t and chloroform-t measured in amine buffer solutions show simple general base catalysis and give Brernsted relations with essentially unit exponents: 0.05 for phenylacetylene and p = 1.12 * 0.05 for chloroform. These results are taken to indicate that proton transfer is rapid and reversible and separation of the proton transfer products is the rate-determining step in these reactions, Le., that phenylacetylene and chloroform are functioning as normal (in the Eigen sense) rather than as pseudo acids. Arguments based upon Marcus and Lewis-More O'Ferrall rate theory are made in support of this view. The data are also used to estimate aqueous solution pK,'s from these carbon acids: pK, = 20.0 for phenylacetylene and 24.1 for chloroform. = 0.99

We wish to report evidence that the tunnel effect makes an important contribution to hydrogen isotope effects in proton transfers but does not control the form of the dependence of the isotope effect on the strength of the attacking base.

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Carbon-13 isotope effects at C-2 have been determined on the rates of elimination from 2phenylethyl-dimethylsulphonium and -trimethylammonium salts with hydroxide ion in mixtures of dimethyl sulphoxide and water. The effects are consistently larger than those predicted from model calculations for a semi-classical (without tunnelling) isotope effect. The most reasonable interpretation is that the form of the dependence of the isotope effect on solvent composition is controlled by the semiclassical effect with a substantial tunnel effect superimposed.

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