MCAT Question A Day - 3/5/14 - Answer!
The following two reactions were carried out.
The rate constant kI was seven times greater than the rate constant kII. Therefore,
A. the rate-determining step involves the breaking of a beta-carbon-hydrogen bond.
B. the rate-determining step involves the breaking of the carbon-bromine bond.
C. the rate of the reaction does not depend on the breaking of a carbon-hydrogen bond.
D. the rate of the reaction does not depend on the breaking of the carbon-bromine bond.
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The correct answer is (A). A bond to deuterium is broken more slowly than a bond to protium (H). Observation of such a primary hydrogen isotope effect elucidates the rate-determining step in a reaction.
