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🥼organic chemistry review

Disubstituted Alkenes

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

Definition

Disubstituted alkenes are organic compounds that contain a carbon-carbon double bond with two substituents attached to each carbon atom of the double bond. These types of alkenes are particularly relevant in the context of understanding the stability of alkenes and the hydration of alkenes through the process of hydroboration.

5 Must Know Facts For Your Next Test

  1. Disubstituted alkenes are more stable than monosubstituted alkenes due to increased electron delocalization and steric factors.
  2. The stability of disubstituted alkenes follows the trend: trans > cis, with the trans isomer being more stable.
  3. Hydroboration-oxidation is a method for the addition of water (H2O) to alkenes, producing alcohols.
  4. The regiochemistry of hydroboration-oxidation of disubstituted alkenes results in the formation of the more substituted alcohol.
  5. Steric factors play a significant role in determining the stability and reactivity of disubstituted alkenes.

Review Questions

  • Explain the factors that contribute to the stability of disubstituted alkenes compared to monosubstituted alkenes.
    • Disubstituted alkenes are more stable than monosubstituted alkenes due to increased electron delocalization and steric factors. The presence of two substituents on each carbon of the double bond allows for greater dispersal of the pi electrons, resulting in greater stability. Additionally, the steric interactions between the substituents can influence the stability, with the trans isomer being more stable than the cis isomer due to reduced steric strain.
  • Describe the regiochemistry of the hydroboration-oxidation reaction of disubstituted alkenes and explain the factors that determine the preferred product.
    • In the hydroboration-oxidation reaction of disubstituted alkenes, the borane reagent initially adds to the less substituted carbon of the double bond, followed by oxidation to form the more substituted alcohol. This regiochemistry is determined by the steric factors, where the bulky borane reagent preferentially adds to the less hindered carbon. The formation of the more substituted alcohol is favored as it is the more stable product, reflecting the Markovnikov's rule of addition to alkenes.
  • Analyze how the stability of disubstituted alkenes can impact their reactivity and the outcome of reactions, such as hydroboration-oxidation.
    • The stability of disubstituted alkenes, which is influenced by factors like electron delocalization and steric effects, can have a significant impact on their reactivity and the outcome of reactions. For example, in the hydroboration-oxidation of disubstituted alkenes, the relative stability of the cis and trans isomers can determine the preferred regiochemistry of the reaction. The more stable trans isomer may be less reactive towards the borane reagent, leading to a greater proportion of the more substituted alcohol product. Additionally, the overall stability of disubstituted alkenes can affect their susceptibility to other types of reactions, such as electrophilic addition or elimination, thereby influencing the synthetic strategies employed in organic chemistry.