DEUTERIUM KINETIC ISOTOPE EFFECTS: V TEMPERATURE DEPENDENCE OF Β-Deuterium EFFECTS IN WATER SOLVOLYSIS OF ISOPROPYL COMPOUNDS

Abstract

The secondary 8-deuterium isotope effect ( k n / k~) has been measured over a range of temperature for the water solvolysis reactions of isopropyl ~nethanesnlphonate, p-toluenesulphonate, and bromide. In these cases the isotope effect is due to a difference in entropies of activation of the isotopic analogues rather than a difference in the enthalpies of activation. I t is suggested that the observed isotope effect is due to internal rotatio~lal effects of the methyl groups in the isopropyl radical, and the lack of an isotope effect on the enthalpy of activation is accounted for by a cancellation of an effect from this source and one from zero-point energy.

Kinetics and mechanisms of the reactions of organic cation radicals and dications. IV. First- and second-order reactions of thianthrene cation radical with phenol

“…An eightfold decrease in [TFA] brought about a 3 X 103-fold increase in the rate (runs 39 and 42). That the reaction is first order in phenol was demonstrated by the direct proportionality between &obsd and [PHOH] (runs 18-24, [25][26][27]33). The dependence of kobsd upon unoxidized TH was derived at two different [PHOH] (runs 18-24, 28-31 with [PHOH] = 2 X 10"3 M and runs 32-37 with [PHOH] = 5 X "3 M).…”

E2C mechanism in elimination reactions. VII. Secondary kinetic hydrogen isotope effects in E2 reactions of alicyclics

“…However, although primary hydrogen isotope effects are certainly temperature dependent,23 secondary hyperconjugative isotope effects have been found to vary much less with temperature37 and in some cases to be actually temperature independent. 38 If we assume that secondary isotope effects are the same at 75 and 50°for the reactions in Chart II we can then substitute our value for B into eq 2 and obtain A = 2.14 at 50°w hich can be extrapolated to 75°u sing Melander's data23 to give A = 1.90 at 75°S ubstitution of A and B in eq 3 leads to C =1.20 at 75°T hese derived isotope values are not significantly changed even if secondary isotope effects are slightly temperature dependent to the extent observed by other workers. 37 The component isotope effects thus found for the chloride ion promoted E2 reactions shown in Chart II are consistent with the isotope effects found in this work for reactions of cyclohexyl tosylate with other bases (see Table IV).…”

Secondary Kinetic Isotope Effects in Bimolecular Nucleophilic Substitutions. VI. Effect of α and β Deuteration of Alkyl Halides in their Menschutkin Reactions with Pyridine in Nitrobenzene

“…Since the hydrolysis reactions give a temperature independent isotope effect for isopropyl compounds (26), it is not possible to specify the origin of the isotope effects in the pyridine reaction. However, that normal effects are observed does allow the conclusion that within the SN2 mechanism there is a trend to a less crowded (or possibly a more SN1-like) transition state for secondary compounds than for primary compounds, since this type of structure is required for normal isotope effects whether the explanation is made in terms of the hyperconjugative effects (27) or in terms of internal rotational contributions (26,28).…”