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🥼organic chemistry review

T-Butyl Cation

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

The t-butyl cation is a carbocation with the formula (CH3)3C+, where a positively charged carbon atom is surrounded by three methyl groups. This highly stabilized carbocation is a key intermediate in various organic reactions, particularly the SN1 mechanism.

5 Must Know Facts For Your Next Test

  1. The t-butyl cation is a highly stabilized carbocation due to the phenomenon of hyperconjugation, which allows for the delocalization of the positive charge.
  2. The three methyl groups surrounding the positively charged carbon atom provide significant stabilization through the donation of electron density from their sigma bonds.
  3. The t-butyl cation is a key intermediate in the SN1 (Nucleophilic Substitution, Unimolecular) reaction mechanism, where it is formed as a result of the loss of a good leaving group.
  4. The stability of the t-butyl cation makes it a favorable intermediate in SN1 reactions, as it can be readily attacked by a nucleophile to form the substitution product.
  5. The formation of the t-butyl cation is often the rate-determining step in SN1 reactions, as the generation of this stable intermediate is the most challenging part of the mechanism.

Review Questions

  • Explain how the structure of the t-butyl cation contributes to its stability.
    • The t-butyl cation is a highly stabilized carbocation due to the phenomenon of hyperconjugation. The three methyl groups surrounding the positively charged carbon atom allow for the delocalization of the positive charge, as the sigma bonds of the methyl groups can donate electron density to the empty p orbital of the carbocation. This extensive stabilization through hyperconjugation makes the t-butyl cation a favorable intermediate in SN1 reactions, where its formation is often the rate-determining step.
  • Describe the role of the t-butyl cation in the SN1 reaction mechanism.
    • The t-butyl cation is a key intermediate in the SN1 (Nucleophilic Substitution, Unimolecular) reaction mechanism. In an SN1 reaction, the first step involves the formation of a carbocation intermediate, which is often the t-butyl cation in the case of tertiary alcohols or alkyl halides. The stability of the t-butyl cation makes it a favorable intermediate, as it can be readily attacked by a nucleophile to form the substitution product. The formation of the t-butyl cation is typically the rate-determining step in SN1 reactions, as the generation of this stable intermediate is the most challenging part of the mechanism.
  • Analyze the importance of the t-butyl cation in the context of the characteristics of the SN1 reaction.
    • The t-butyl cation is a crucial intermediate in the SN1 reaction mechanism due to its high degree of stability. The extensive stabilization of the t-butyl cation through hyperconjugation is a key characteristic of the SN1 reaction, as it allows for the formation of a stable carbocation intermediate that can be readily attacked by a nucleophile. The stability of the t-butyl cation makes it a favorable intermediate, and its formation is often the rate-determining step in SN1 reactions. This stability also contributes to the stereochemical outcome of the SN1 reaction, as the t-butyl cation can be attacked by the nucleophile from either side, leading to the formation of a racemic mixture of products.