Tert-Butyl

Definition

The tert-butyl group is a branched alkyl substituent with the chemical formula (CH3)3C-. It is a tertiary alkyl group, meaning the carbon atom to which the three methyl groups are attached is also bonded to another carbon atom. This structural feature gives the tert-butyl group unique properties that are relevant in the context of organic chemistry topics such as alkyl groups, the stability of alkenes, reactions of ethers, and conjugate carbonyl additions.

5 Must Know Facts For Your Next Test

1. The tert-butyl group is a bulky, highly branched alkyl substituent that can provide steric hindrance in organic reactions.
2. The stability of the tert-butyl group is attributed to hyperconjugation, which delocalizes the positive charge in a carbocation intermediate.
3. Ethers containing a tert-butyl group are more resistant to acidic cleavage due to the steric hindrance around the ether oxygen.
4. In the Michael reaction, a tert-butyl substituent on the acceptor can enhance the rate and stereoselectivity of the conjugate addition.
5. The tert-butyl group is often used as a protecting group in organic synthesis due to its stability and ease of removal.

Review Questions

• Explain how the structure of the tert-butyl group contributes to the stability of alkenes.
  • The tert-butyl group is a highly branched alkyl substituent, which means the carbon atom to which the three methyl groups are attached is also bonded to another carbon atom. This tertiary carbon configuration allows for effective delocalization of the positive charge in a carbocation intermediate through hyperconjugation. The stabilization provided by hyperconjugation makes the tert-butyl group a favorable substituent on alkenes, as it can stabilize the carbocation-like transition state during electrophilic addition reactions.
• Describe the role of the tert-butyl group in the reactivity of ethers during acidic cleavage.
  • Ethers containing a tert-butyl group are more resistant to acidic cleavage compared to other alkyl-substituted ethers. This is due to the bulky, highly branched nature of the tert-butyl group, which creates significant steric hindrance around the ether oxygen. This steric hindrance makes it more difficult for the acid to approach and cleave the ether bond, resulting in increased stability and reduced reactivity under acidic conditions.
• Analyze how the presence of a tert-butyl substituent on the acceptor can influence the outcome of a Michael reaction.
  • In the Michael reaction, a conjugate addition of a nucleophile to an α,β-unsaturated carbonyl compound, the presence of a tert-butyl group on the acceptor can enhance both the rate and stereoselectivity of the reaction. The bulky tert-butyl group can provide steric hindrance that favors the approach of the nucleophile from the less hindered side, leading to improved stereoselectivity. Additionally, the stabilizing effect of the tert-butyl group on the resulting enolate or enolate-like intermediate can increase the rate of the conjugate addition, making the reaction more kinetically favorable.

Related terms

Alkyl Group: An alkyl group is a hydrocarbon substituent derived from an alkane by the removal of one hydrogen atom.

Hyperconjugation: Hyperconjugation is a stabilizing interaction between a σ-bond (typically a C-H bond) and an adjacent π-bond or lone pair of electrons.

Carbocation: A carbocation is a positively charged carbon atom with only three bonds, often an intermediate in organic reactions.