Organic Chemistry: Sn1E1 Reactions

Topics

Organic Chemistry: Sn1E1 Reactions SN1 and E1 Reactions

Save

Topics Organic Chemistry: Sn1E1 Reactions SN1 and E1 Reactions

S_N2 and E2 vs. S_N1 and E1

The S_N2 and E2 mechanisms require a good nucleophile or a strong base. In contrast, S_N1 and E1 mechanisms need weak nucleophiles and bases.

The nucleophiles and bases in S_N1 and E1 reactions aren't strong enough to eject the leaving group by themselves. Instead, both S_N1 and E1 reactions are characterized by the formation of a common carbocation intermediate. Even weak bases and poor nucleophiles will react with the carbocation.

Consequences of the Carbocation Intermediate

The carbocation intermediate lends a number of unique features to S_N1 and E1 reactions. First, both mechanisms require a stable carbocation intermediate. Thus S_N1 and E1 will only work for secondary or tertiary α-carbons**. Second, S_N1 and E1 reactions involve a carbocation intermediate and are not concerted. Because of the geometry of the carbocation and their non- concerted nature, both reactions result in a loss of stereochemical configuration. Third, S_N1 and E1 reactions are favored by polar, protic solvents. Polar, protic solvents stabilize the carbocation. Fourth, secondary carbocations may rearrange to form tertiary carbocations. This greatly increases the number of products.