Deuterium effect

Chung and coworkers tried to observe similar species in y-irradiated DMSO-h6 at 77 K, however, repeated attempts were unsuccessful. Besides no free -CH3 radicals were detected in the y-irradiated DMSO-h6. They suggested that this remarkable difference of an all-or-nothing deuterium effect might be connected with the very much larger reactivity of the methyl radical in a subsequent reaction of hydrogen abstraction due to the greater reactivity of the C—H over the C—D bond. 

Dethionylation 462 Detosylation 940 Deuterium effects 892, 898 Dewar benzenes 651... 

The j8-deuterium effect was studied and discussed in detail in a later... 

The dependence of the j3-deuterium effect on the spatial orientation of the isotopic bond with respect to the developing -orbital, on the a-carbon atom was elegantly demonstrated by Shiner and Humphrey (1963). This work will not be discussed in detail here suffice it to say the suggestion is made that j8-deuterium effects are better correlated by the postulate of hyperconjugation and its angular dependence than by the simple steric model (Shiner and Humphrey, 1963). 

The aforementioned deuterated derivatives were prepared by way of reduction of a ketone, aldehyde, or ester with sodium borodeu-teride, or by deuteroboration of an alkene. An interesting reaction, perhaps eventually applicable to direct deuteration of polysaccharides, was reported by Koch and Stuart413 and by them and their coworkers,41b who found that treatment of methyl a-D-glucopyranoside with Raney nickel catalyst in deuterium oxide results in exchange of protons attached to C-2, C-3, C-4, and C-6. In other compounds, some protons of CHOH groups are not replaced, but the spectra may nevertheless be interpreted with the aid of a- and /3-deuterium effects. 

Considering the deuterium effect on naphthalene, Ci0H8, in which all the hydrogen atoms are replaced by deuterium, the Franck-Condon factor is decreased and consequently the rate of internal conversion... 

The hydroxo complex [D] is assumed to rearrange to the cr-bonded compound [A] since only a secolidary isotope effect is observed with C2D4, and if the n complex went directly to acetaldehyde Henry claims that the hydride shift involved would have produced a primary deuterium effect. Although the hydroxo complex [D] would have been expected to be traris, it was suggested that kinetically significant amounts of the cis isomer are present. 

This mechanism seems to imply that if some substitution occurs at the classical position of attack (the first a-complex), then such a substitution should show the deuterium isotope effect for proton loss from this position. The deuterium effect is absent in the majority of nitration cases, except for nitration in sterically shielded positions (Schoffield 1980). Perhaps a systematic investigation of... 

The formation of acrolein comprises several steps. The first and ratedetermining step is generally assumed to be abstraction of an allylic hydrogen atom. Evidence is provided from several sources, e.g. the deuterium effect of the reaction (Adams [2]) and the analogy between oxidation and DzO exchange (Christie et al. [86]), and for various catalysts. 

The very rapid conversion of 2-propanol to acetone under these conditions can be consistent with such a mechanism, although it conflicts with the deuterium effect for the central H-atom reported by Buiten. The high velocity of the 2-propanol oxidation, on the other hand, hampers the finding of clear evidence in favour of one of the above mechanisms. 

The relation between the acid strength of the catalysts and the mechanism has also been demonstrated by correlations [55,123] of the reaction parameter, p, of the Taft equation for the dehydration of secondary alcohols on A1203 + NaOH, Zr02, Ti02 and Si02 (see Table 4) with the sensitivity to pyridine poisoning, the heat of adsorption of water and diethylether and the kinetic isotope deuterium effects (Table 3) on the same catalysts (Fig. 5). The parameter p reflects the mechanism being... 

Figure 3.35 The deuterium effect in non-radiative transitions. The spacing of the vibrational levels of CD (carbon-deuterium) is much smaller than that of CH, so that for the same energy gap a much more distorted geometry of RD must be reached...

N-Deuterium Effect on Ratio of Trans to Total Non-Geminal Isomers in Reaction... 

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