Two alternative mechanisms have been proposed for the acid-catalyzed hydration of an…
CHEMISTRY · Multi-part · A Level · Chemistry · Introduction to organic chemistry · Introduction to organic chemistry
Problem
Two alternative mechanisms have been proposed for the acid-catalyzed hydration of an alkene to form an alcohol.
Mechanism A
1. H3O++C2H4→C2H5++H2O (slow)
2. C2H5++H2O→C2H5OH+H3O+ (fast)
Mechanism B
1. H2SO4+C2H4→C2H5HSO4 (slow)
2. C2H5HSO4+H2O→C2H5OH+H2SO4 (fast)
Assume that no other elementary steps occur in either mechanism and that each mechanism, if correct, completely accounts for the observed macroscopic reaction.
A research team seeks to determine which mechanism is correct.
(a) For each mechanism, write the overall balanced chemical equation obtained by summing its elementary steps and canceling species that appear on both sides.
(b) For each mechanism, identify the species that fulfills the role of a catalyst. Provide specific evidence from the elementary steps and the overall equation to support your identification.
(c) Design an experiment that would distinguish between Mechanism A and Mechanism B by monitoring the concentrations of one or more species over time. Clearly state what measurements you would make, what result you would expect for each mechanism, and how the result would allow you to choose between the mechanisms.
(d) Discuss how the identification of the catalyst in the correct mechanism explains the effect of solution pH on the reaction rate.