Question

Conversion of cyclohexene to cyclohexanol can be conveniently achieved by (a) hyboration-hydrolysis (b) hydroboration-oxidation (c) \(\mathrm{NaOH}-\mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{Br}_{2}-\mathrm{H}_{2} \mathrm{O}\)

Short answer

The correct answer is (b) hydroboration-oxidation.

Step-by-step solution

Understand the Starting Material

The starting material given is cyclohexene, which is an alkene with a double bond within a six-carbon ring.

Desired Product

The target conversion is to cyclohexanol, indicating that an alcohol group (-OH) should replace the double bond in cyclohexene.

Determine Reaction Type Needed

To convert an alkene (cyclohexene) to an alcohol (cyclohexanol), a reaction involving the addition of -OH across the double bond is needed.

Evaluate Options

Examine the provided options: - Option (a) "hyboration-hydrolysis" may be a misspelling or misconception as it does not directly relate to common reactions. - Option (b) "hydroboration-oxidation" is a well-known reaction sequence for converting alkenes to alcohols, involving the addition of water across the double bond. - Option (c) "NaOH-H2O" typically involves a basic environment without specific mechanisms to add -OH across a double bond. - Option (d) "Br2-H2O" involves electrophilic addition of bromine, which does not convert alkenes to alcohols.

Choose the Correct Reaction

Hydroboration-Oxidation is the correct approach: 1. Hydroboration step: BH3 is added to the double bond. 2. Oxidation step: H2O2/NaOH is used to replace the boron group with an -OH group. This results in the formation of cyclohexanol from cyclohexene.

Key concepts

Hydroboration-Oxidation

Hydroboration-Oxidation is a two-step reaction process utilized in organic chemistry for the conversion of alkenes into alcohols. This reaction is often favored due to its regioselectivity and stereospecificity. It provides a way to add a hydroxyl group (-OH) across a double bond, transforming an unsaturated compound such as an alkene into a saturated alcohol.

• Hydroboration Step: In this initial stage, borane (BH₃) or a related reagent is added across the double bond of the alkene. The boron atom attaches to the less substituted carbon, while hydrogen attaches to the more substituted carbon. This selective addition is known as anti-Markovnikov addition.
• Oxidation Step: The subsequent step involves treating the organoborane with hydrogen peroxide (H₂O₂) and sodium hydroxide (NaOH). This results in the replacement of the boron atom with an -OH group, forming the alcohol.

The entire process is typically stereospecific, meaning the configuration of the starting material is preserved in the product, ensuring that no rearrangements occur. Overall, hydroboration-oxidation is a practical and useful method for obtaining alcohols from alkenes in organic synthesis.

Cyclohexene to Cyclohexanol Conversion

Cyclohexene is a cyclic alkene, which makes it an excellent candidate for oxidation reactions that transform it into an alcohol. Converting cyclohexene into cyclohexanol is a classic example of hydroboration-oxidation in action.

• Starting Material: Cyclohexene, with its six-carbon ring and present double bond, forms the basis for the reaction.
• Reaction Mechanism: In the hydroboration step, BH₃ adds across the double bond of cyclohexene. This results in the formation of a trialkylborane intermediate.
• Oxidation Outcome: Subsequent oxidation with H₂O₂ and NaOH transforms the trialkylborane into cyclohexanol. The location of the -OH group is derived from the former position of the boron atom during the hydroboration step.

This transformation exemplifies how straightforward alkene conversion can be, demonstrating the value of hydroboration-oxidation methodology in producing targeted alcohol derivatives from unsaturated hydrocarbons.

Alcohol Synthesis from Alkenes

Synthesizing alcohols from alkenes through the hydroboration-oxidation route is an elegant and precise method. This transformation is efficient, providing high yields with minimal byproducts.

• Regioselectivity and Stereospecificity: The anti-Markovnikov addition ensures that the hydroxyl group attaches to the less substituted carbon, a feature particularly advantageous when working with complex molecules.
• Simplicity of Procedure: The reactions are conducted under mild conditions, typically at room temperature, and are generally free from harsh reagents, making it accessible for a range of experimental setups.
• Applications: This methodology is widely employed in the synthesis of complex natural products and pharmaceuticals, where the precise placement of functional groups is crucial.

By understanding the fundamental principles underlying this reaction, chemists can apply it to design efficient synthetic pathways, ultimately expanding the diversity of alcohols accessible from simple alkene starting materials.