Multiple Choice
Which of the following could not clearly be a contributor to general acid-base catalysis (circle all that apply)?
6. Enzymes and Enzyme Kinetics
Catalysis
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The catalytic mechanism below is an example of:
A
General acid catalysis.
B
Specific acid catalysis.
C
General base catalysis.
D
Specific base catalysis.
Verified step by step guidance1
Examine the mechanism provided in the image. Notice that the reaction involves a nucleophilic attack by a hydroxide ion (OH-) on the carbonyl carbon of an ester, leading to the formation of a tetrahedral intermediate.
Observe that the imidazole group (in red) is involved in the reaction. It is acting as a base, accepting a proton from the hydroxide ion, which facilitates the nucleophilic attack.
In the second step, the tetrahedral intermediate collapses, leading to the expulsion of the leaving group (the alcohol part of the ester), and the imidazole group donates a proton back to the leaving group.
This mechanism is an example of general base catalysis because the imidazole group is acting as a base to facilitate the reaction by accepting a proton, which is a characteristic of general base catalysis.
General base catalysis involves a base that is not the solvent (water) accepting a proton to increase the nucleophilicity of a reactant, which is what is observed in this mechanism with the imidazole group.
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