Primary kinetic isotope effect of sulfur

The lighter the element, the larger is the ratio of the heavy and the light isotope masses. Thus, the ratio of deuterium and hydrogen masses is 2/1, and that of sulfur-34 and sulfur-32 is 34/32 = 1.0625. This is why the primary kinetic isotope effect of deuterium is relatively high compared to that of sul-fur-34. Consequently, the lowering of the zero-point energies is 

Although the sulfur isotope effect is small, its determination might be very useful in studies of reaction mechanisms. This can be shown on the following example the hydrolysis of tert-butyldimethylsulfonium iodide proceeds according to the scheme  

Reactions (1.14.9) and (1.14.10) have to be taken into consideration, since there is about 95.1% of and 4.2% of in nature. Isotopes (0.74%) and (0.016%) are not taken into account because of their small concentrations. 

Relatively slow reactions (1.14.9) and (1.14.10) are followed by the fast reaction  

The reaction products are ter/-butyl alcohol, and I. The reaction rate can be conveniently followed at 60 °C by titration of cooled aliquots with sodium hydroxide. It should be assumed that slow reaction steps (1.14.9) and (1.14.10) involve breakage of the C-S bonds, that these steps are rate determining and that the C-S bonds are almost broken in the reaction transition state. If so, the rates of formation of reaction products with light and heavy isotopes are given by the first order rate equations  

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