Bases in proton transfer, reacting

ACS Symposium Series American Chemical Society Washington, DC, 1975. 

Having, thus far, given a very brief survey of the general shape of the theory and results on primary isotope effects in thermal reactions, I would like next to turn to secondary isotope effects. Here,for the sake of simplicity and brevity, will confine my examples to the isotopes of hydrogen,since secondary isotope effects are usually so small that their reliable observation is difficult and they have been reported for isotopes other than those of hydrogen in only a few instances. It is convenient to divide secondary isotope effects into at least two kinds (one of which could be further subdivided)  

The second general kind of secondary isotope effects are those caused by isotopic substitution at positions in the molecule more remote from the reaction center. There are two general possible causes for such effects. 

Many isotope effects due to substitution of deuterium for hydrogen at positions g- or more remote from the reaction center have been observed. (18) There is only space here to refer the reader to more detaile3 summaries or to the original literature and to comment that each of the big three mechanisms of intramolecular interaction between reaction and isotopic centers has been shown in one case or another to cause isotope effects 1) Hy-perconjugative electron release from a C-H bond causes normal 

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