Why do the SN 1 / E 1 reactions of tertiary alkyl halides favor the substitution product?

Name: Problem 22, Chapter 8: Essential Organic Chemistry
Uploaded: 2021-07-16T18:42:51-08:00
Duration: 3 min 32 s
Channel: Joshua Gibson
Description: Why do the SN 1 / E 1 reactions of tertiary alkyl halides favor the substitution product?

step 1 this question covers predicting the products of S &1 and S &2 reactions. And to start with, we a

Why do the SN 1 / E 1 reactions of tertiary alkyl halides...

Key Concepts

Carbocation Stability

Tertiary alkyl halides lead to the formation of stabilized carbocation intermediates once the leaving group departs. The high degree of alkyl substitution provides electron-donating inductive effects and hyperconjugation, which effectively delocalize the positive charge. This increased stability is crucial in unimolecular reaction pathways and makes the subsequent formation of products more feasible.

Unimolecular Reaction Mechanisms (SN1 and E1)

Both SN1 and E1 mechanisms proceed via the initial formation of a carbocation intermediate in a rate-determining step. In the SN1 pathway, a nucleophile quickly attacks the carbocation to form a substitution product, whereas in the E1 pathway, a base abstracts a proton leading to the formation of an alkene. The competition between these pathways is influenced by factors such as the nature of the nucleophile/base and the reaction environment.

Reaction Conditions Influencing Product Outcome

The predominance of substitution over elimination in these reactions often stems from choices in reaction conditions. Polar protic solvents, commonly used in SN1 reactions, stabilize both the carbocation and the leaving group, and typically support the attack by a relatively weak nucleophile over deprotonation. Additionally, if the reaction is carried out at lower temperatures or with weaker bases, the pathway leading to substitution is arithmetically favored over elimination.

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