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🥼organic chemistry review

Tertiary Alkyl Halide

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

Definition

A tertiary alkyl halide is a type of organic compound where a halogen atom (such as chlorine, bromine, or iodine) is bonded to a carbon atom that is also connected to three other carbon atoms. This unique structure and bonding arrangement give tertiary alkyl halides distinct chemical properties and reactivity compared to other alkyl halides.

5 Must Know Facts For Your Next Test

  1. Tertiary alkyl halides are more stable and less reactive compared to primary and secondary alkyl halides due to the presence of the three alkyl groups attached to the carbon bearing the halogen.
  2. Tertiary alkyl halides undergo $\text{S}_\text{N}1$ (Nucleophilic Substitution, Unimolecular) reactions more readily than $\text{S}_\text{N}2$ (Nucleophilic Substitution, Bimolecular) reactions.
  3. The increased stability of tertiary alkyl halides is due to the ability to form a more stable carbocation intermediate during $\text{S}_\text{N}1$ reactions.
  4. Tertiary alkyl halides are less susceptible to elimination reactions compared to primary and secondary alkyl halides.
  5. The steric hindrance around the carbon-halogen bond in tertiary alkyl halides makes it more difficult for nucleophiles to approach and displace the halogen.

Review Questions

  • Explain how the structure of a tertiary alkyl halide influences its reactivity compared to primary and secondary alkyl halides.
    • The presence of three alkyl groups attached to the carbon bearing the halogen in a tertiary alkyl halide increases the stability of the molecule and the resulting carbocation intermediate formed during $\text{S}_\text{N}1$ reactions. This makes tertiary alkyl halides less reactive towards nucleophilic substitution reactions, favoring $\text{S}_\text{N}1$ over $\text{S}_\text{N}2$ mechanisms. Additionally, the steric hindrance around the carbon-halogen bond makes it more difficult for nucleophiles to approach and displace the halogen, further reducing the reactivity of tertiary alkyl halides compared to primary and secondary alkyl halides.
  • Describe the key factors that contribute to the increased stability of tertiary alkyl halides.
    • The increased stability of tertiary alkyl halides is primarily due to the ability to form a more stable carbocation intermediate during $\text{S}_\text{N}1$ reactions. The presence of three alkyl groups attached to the carbon bearing the halogen provides greater electron-donating stabilization to the partial positive charge developed in the carbocation intermediate. This stabilization makes the formation of the carbocation more favorable, leading to the increased reactivity of tertiary alkyl halides towards $\text{S}_\text{N}1$ mechanisms. Additionally, the steric hindrance around the carbon-halogen bond makes it more difficult for nucleophiles to approach and displace the halogen, further contributing to the reduced reactivity of tertiary alkyl halides.
  • Analyze the differences in the reactivity of tertiary alkyl halides compared to primary and secondary alkyl halides, and explain how these differences impact their respective reaction pathways.
    • Tertiary alkyl halides are significantly less reactive compared to primary and secondary alkyl halides due to their unique structural features. The presence of three alkyl groups attached to the carbon bearing the halogen provides greater stabilization to the carbocation intermediate formed during $\text{S}_\text{N}1$ reactions, making this pathway more favorable for tertiary alkyl halides. Conversely, the steric hindrance around the carbon-halogen bond makes it more difficult for nucleophiles to approach and displace the halogen, reducing the likelihood of $\text{S}_\text{N}2$ reactions. This contrasts with primary and secondary alkyl halides, which are more susceptible to $\text{S}_\text{N}2$ mechanisms due to their lower steric demands. Additionally, tertiary alkyl halides are less prone to elimination reactions compared to their primary and secondary counterparts. These differences in reactivity have significant implications for the synthetic pathways and reaction mechanisms involving tertiary alkyl halides in organic chemistry.