Deuteron transfer

The conductivity of DC1 in D20 solution depends to a large extent on the ease with which a deuteron can jump from a (D30)+ ion to an adjacent D20 molecule. From the value given for DC1 in Table 7 it is clear that such deuteron transfers take place with greater difficulty than the corresponding proton transfers in H20 see Sec. 79. 

The Dissociation Constant of Nitric Add. Alodcrately Weak Acids. The Variation of J with Temperature. Proton Transfers between Solute Particles. A Proton Transfer in Methanol Solution. Proton Transfers with a Negative Value for. / . The Hydrolysis of Salts. Molecules with Symmetry. Substituted Ammonium Ions. Deuteron Transfers in D2(). The Dissociation of Molecular Ions. 

Deuteron Transfers in D20. As shown in Table 1 the characteristic temperature d for the dielectric constant of D20 is almost the same as for H20. The values of the dielectric constant of D20 are given with... 

These observations indicate conclusively that the ionic sequence responsible is a proton and deuteron transfer sequence. Individual steps in... 

Effects of Temperature on Ionic Reactions in TD/D2 CH4/ CD4. Observation that the methanium ion proton (deuteron) transfer sequence fails to exhibit a temperature coefficient within experimental uncertainties leads unavoidably to the conclusion that none of the reactions from 1 to 12 requires thermal activation between —78° and 25°C. From Equations I, II, III, appropriate steady state assumptions, and representing both neutralization steps by kX2, we find that... 

Ionic Reactions in TD/D2 Ethane Mixtures. The data in Table III show that deuteron transfer occurs in irradiated mixtures of D2 and ethane as well. Data are shown only for temperatures (<25°C.) at which ionic reactions clearly predominate. Analysis of data concerning thermal atomic and free-radical reactions at higher temperatures will be published elsewhere in the near future. The reaction of D3 + with ethane has been observed directly (1) and postulated (2) by other workers. Both groups have proposed that the sequence initiated by deuteron transfer to ethane proceeds as follows ... 

Two parameters that are accessible to the experimentalist have been the effect of the interchange of a deuteron for a proton upon the dynamics of transfer and the effect of temperature variation upon the kinetics of proton-deuteron transfer [49]. As previously mentioned, the semiclassical model has been employed in the rationalization of kinetic deuteron isotope effects that exceed the factor of 7.0, the maximum predicted by the classical model [5]. However, the full quantum model also allows for the wide range in the kinetic deuteron isotope effect, the range of which overlaps that predicted by the semiclassical model [53]. Thus, the kinetic deuteron isotope effect in and of itself cannot be used to distinguish between the two models. 

The Truhlar group has reported an interesting theoretical study of H/D kinetic isotope effects for conversion of 2 phospho-D-glycerate to phosophoenolpyruvate catalyzed by the yeast enolase enzyme. The proton transfer step (first reaction step in Fig. 11.10) is the rate limiting step and was chosen for theoretical study. The KIE for proton/deuteron transfer is kn/kD = 3.3 at 300 K. 

Finally, two studies have reported on the reactions of carbocations with Mg atoms using mass spectrometry The types of products formed depend on the nature of the carbocation. The labeled methanium ion, CH4D+, reacts via proton transfer (equation 11), deuteron transfer (equation 12) and charge transfer (equation 13). The ethyl cation reacts via charge transfer (equation 14) while the tert-butyl cation reacts via proton transfer (equation 15). In all cases there was no evidence for formation of an organomagnesium species. 

In the experiment of proton (respectively deuteron) transfer it is understandable that both the fast component (t i = 0.2 ps) and the... 

To proceed further it is necessary to make some assumption concerning the connection between acidity constant and rate constant of proton (deuteron) transfer ( hl,o or DLao)- A connection is suggested by the Brensted catalysis law (Brensted and Pedersen, 1924 Brensted, 1928) ... 

It should be noted that it is, of course, not permissible to use the Bronsted catalysis law to relate rates of proton transfers to rates of deuteron transfers. No such suggestion is implied by the application of equations (68) and (69). 

H)+ and (D)+ represent the transition states for proton and deuteron transfer, respectively. To an excellent approximation (Bigeleisen, 1955) /cH//cD should be uninfluenced by secondary effects. It has a value very close to that suggested as a maximum by simple theory (Bell, 1959c). 

Nishikawa S, Huang H, Dong SJ. Ultrasonic relaxation kinetics on fast deuteron transfer reaction. J Phys Chem A 1999 103 3804-3808. 

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