Asymmetric hydrogenation deuterium isotope effects

The differences in deuterium and carbon isotope effects indicate the asymmetric transition state with more advanced carbon-carbon bond formation to the terminal Cl atom. The difference between deuterium isotope effects for HCI-S and Htmns hydrogens probably originates from experimental uncertainty. Theoretical calculations (B3LYP/6-31G, B3LYP/6-311+G ) for carbene addition to 1-butene were carried out for two modes with carbene approaching carbon atom Cl or C2. The best agreement for experimental isotope effects is for carbene attack on terminal carbon atom and the carbene-alkene separation in the transition state of 2.5 A. 

Isotope effects on chemical shifts can be used to reveal tautomeric equilibria in symmetric as well as asymmetric tautomeric systems. The isotope effects may also provide information about hydrogen-bond potentials. A number of different isotope effects, short-range as well as log-range, may be used. Deuterium isotope effects are by far the most useful, both from an effect point of view and also because deuterium is easy to introduce in most situations. Heavy isotopes are not used extensively. and are excellent as observing nuclei for secondary isotope... 

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