C344 Homework #1: Review of mechanism and arrow pushing
Mechanism is primarily an explanation of “how” a reaction occurs in terms of bond changing.
Therefore, a real understanding of mechanism is demonstrated by how you are able to answer
questions about reaction mechanism in written statements. Arrow mechanisms are only a short-hand
expression of understanding—they don’t replace a real understanding. But at the same time, they are
the expression that most chemists use most of the time, so we need to be able to use arrows!
1. Answer the following questions in short statements (no arrows.)
A. What is the difference between an SN1 substitution mechanism and an SN2 mechanism?
B. Write a short paragraph of the mechanism of this reaction under E1 conditions. Write a
paragraph for the reaction under E2 conditions.
C. Once the intermediate is formed in this reaction, why is it more likely to go on to products
than to revert to starting material?
D. Why is acid needed to catalyze this reaction? Why is it considered a catalyst, not a reagent?
E. Why is the mechanism of the Diels-Alder reaction considered to be “concerted?” How does
this mechanism explain the sterespecificity?
2. Provide full arrow-pushing mechanisms for each of these reactions. Label each of them with one of
these names: nucleophilic addition, nucleophilic acyl substitution, electrophilic addition, electrophilic
aromatic substitution, nucleophilic aromatic substitution.