Specify reagents suitable for converting 3-ethyl-2-pentene to each of the following:
(a) 2, 3-Dibromo-3-ethylpentane
(b) 3-Chloro-3-ethylpentane
(c) 2-Bromo-3-ethylpentane
(d) 3-Ethyl-3-pentanol
(e) 3-Ethyl-2-pentanol
(f ) 3-Ethyl-2,3-epoxypentane
(g) 3-Ethylpentane
The Correct Answer and Explanation is :
To convert 3-ethyl-2-pentene to the specified compounds, a variety of reagents and reactions can be employed. Here’s a breakdown of the suitable reagents for each transformation:
(a) 2, 3-Dibromo-3-ethylpentane
- Reagents: Bromine (Br₂) in CCl₄ or with UV light
- Explanation: This reaction involves the addition of Br₂ to the alkene. The addition of Br₂ across the double bond occurs via an anti addition, resulting in the formation of 2,3-dibromo-3-ethylpentane. The Br₂ adds across the double bond in an anti-fashion due to the formation of a bromonium ion intermediate.
(b) 3-Chloro-3-ethylpentane
- Reagents: HCl (hydrochloric acid)
- Explanation: The alkene undergoes electrophilic addition of HCl across the double bond. The proton adds to the carbon with the most hydrogen atoms (Markovnikov’s rule), and the chloride ion (Cl⁻) adds to the other carbon. This gives 3-chloro-3-ethylpentane.
(c) 2-Bromo-3-ethylpentane
- Reagents: HBr (hydrobromic acid)
- Explanation: This reaction is similar to the one above but uses HBr. The addition of HBr follows Markovnikov’s rule, with the proton attaching to the carbon atom with the most hydrogen atoms and the bromide ion attaching to the other carbon. This results in the formation of 2-bromo-3-ethylpentane.
(d) 3-Ethyl-3-pentanol
- Reagents: 1) B₂H₆ (diborane), 2) H₂O₂ (hydrogen peroxide), NaOH (sodium hydroxide)
- Explanation: This is a hydroboration-oxidation reaction. In the first step, diborane (B₂H₆) adds to the alkene in an anti-Markovnikov fashion, placing the boron atom at the carbon with the fewest hydrogens. In the second step, oxidation with H₂O₂ and NaOH replaces the boron with a hydroxyl group, resulting in 3-ethyl-3-pentanol.
(e) 3-Ethyl-2-pentanol
- Reagents: 1) BH₃ (borane), 2) H₂O₂, NaOH
- Explanation: Similar to (d), the hydroboration-oxidation reaction will add the hydroxyl group to the 2-position rather than the 3-position. This leads to 3-ethyl-2-pentanol as the final product.
(f) 3-Ethyl-2,3-epoxypentane
- Reagents: Peracid (e.g., m-CPBA or performic acid)
- Explanation: This reaction involves the electrophilic attack of a peracid (such as m-chloroperbenzoic acid, m-CPBA) on the double bond of 3-ethyl-2-pentene. The peracid adds an oxygen atom to the double bond, forming an epoxide ring at the 2,3-positions, resulting in 3-ethyl-2,3-epoxypentane.
(g) 3-Ethylpentane
- Reagents: Hydrogen gas (H₂) with a catalyst (e.g., Pt or Pd)
- Explanation: This is a hydrogenation reaction. The double bond in 3-ethyl-2-pentene is reduced using hydrogen gas in the presence of a metal catalyst such as platinum (Pt) or palladium (Pd). This results in the saturation of the double bond and the formation of 3-ethylpentane.
These reagents are selected based on the type of transformation required (e.g., addition, reduction, oxidation) and the specific position of functional groups in the desired products.