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COMMUNICATIONS TO THE EDITOR
Alternative to Tunneling In Proton-Transfer Reactlons Exhlbiting High Isotope Effects
An explicit expression for the rate constant may be based on the minimal eq 3 as shown in eq 4. The first
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Sir: High kinetic isotope effects in roton transfer reactions have been reported by Lewis‘$ and Caldi1-1~2~ and summarized by BelL5 The conclusions reached after a careful and extensive study by Caldin4 along with discussion of this and other work by workers in the field of proton transfer6 focused on proton tunneling as the explanation for the results. All but one of the cases in which a high isotope effect is found involve a nitroalkane derivative as the proton donor, and hindered bases in medium or low polarity solvents. Another aspect of the behavior of nitroalkanes in proton transfer reactions is that anomalous Bronsted coefficients ( a )(>l,
