Question

Match the following: List I (Compounds to be reduced) 1\. \(\mathrm{BrCH}_{2} \mathrm{CH}_{2} \mathrm{CHO}\) 2\. \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COCH}_{3}\) 3\. \(\mathrm{PhCH}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{COCH}_{2} \mathrm{CH}_{3}\) 4\. \(\mathrm{PhCOCH}_{3}\) List II (most suitable reduction) (i) Clemmensen reduction (ii) Wolf-Kishner reduction (iii) Both The correct matching is: The correct matching is: 1 2 3 4 (a) (iii) (ii) (ii) (i) (b) (i) (ii) (ii) (iii) (c) (i) (iii) (iii) (ii) (d) (ii) (iii) (ii) (i)

Short answer

The correct match is option (a): 1-(iii), 2-(ii), 3-(ii), 4-(i).

Step-by-step solution

Analyze Compound 1

Compound 1 is \( \mathrm{BrCH}_{2} \mathrm{CH}_{2} \mathrm{CHO} \), an aldehyde with bromine. Clemmensen and Wolf-Kishner reductions are typically used for ketones, not aldehydes. Both methods could potentially reduce the carbonyl group, but Clemmensen is the better choice for substrates with sensitive functional groups like bromide.

Analyze Compound 2

Compound 2 is \( \left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COCH}_{3} \), which contains an alcohol and a ketone. Wolf-Kishner reduction is more suitable for converting ketones to alkanes, especially when alcohols are present, as it does not affect them.

Analyze Compound 3

Compound 3 is \( \mathrm{PhCH}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{COCH}_{2} \mathrm{CH}_{3} \), with an alcohol and a ketone. Wolf-Kishner reduction would be the best choice as it directly targets the carbonyl without altering the alcohol group.

Analyze Compound 4

Compound 4 is \( \mathrm{PhCOCH}_{3} \), a pure ketone. Clemmensen reduction is effective for reducing ketones to alkanes even in the presence of unsaturated or aromatic systems.

Match Compounds to Methods

Based on the analyses: 1 -> Clemmensen (i) 2 -> Wolf-Kishner (ii) 3 -> Wolf-Kishner (ii) 4 -> Clemmensen (i)

Verify and Select Answer

Looking at the options given, the correct match for the analysis is in answer option (a) which aligns with our deduced pairings.

Key concepts

Clemmensen Reduction

The Clemmensen reduction is a powerful method used in organic chemistry to convert ketones and aldehydes into alkanes. It involves using zinc amalgam (zinc mixed with mercury) in concentrated hydrochloric acid. This reduction is particularly useful for compounds that have acid-sensitive functional groups.

• Origin: Named after Erik Christian Clemmensen, who developed the technique.
• Key Feature: Best suited for reducing carbonyl groups in aldehydes and ketones while preserving other functional groups that may be heat or base-sensitive.
• Limitations: Generally not suitable for compounds sensitive to acidic conditions.

In the context of the exercise, Clemmensen reduction is favored for substrates like bromides, where exposure to harsh basic conditions or prolonged heating could lead to side reactions.

Wolf-Kishner Reduction

The Wolf-Kishner reduction offers a different approach to reducing carbonyl groups similarly to Clemmensen reduction. Instead of acidic conditions, it operates under strongly basic conditions with hydrazine ((NH\(_2\))\(_2\)H) and a strong base such as potassium hydroxide (KOH). The process converts ketones directly into alkanes.

• Origin: Developed through the work of Nikolai Wolf and Kishner in the early 20th century.
• Compatibility: Ideal for molecules that may have sensitive groups not tolerant of acidic conditions, such as alcohols.
• Advantages: Can be run at relatively high temperatures without affecting stable functional groups such as alcohols.

In practice, the Wolf-Kishner reduction is an excellent choice for reducing ketones in the presence of other functional groups, like alcohols, as it avoids degradation.

Chemistry Problem Solving

Solving chemistry problems effectively requires a combination of theoretical knowledge and analytical skills. When approaching reduction reactions in organic chemistry:

• Understand Reactions: Familiarize yourself with different reduction methods like Clemmensen and Wolf-Kishner, and their appropriate applications.
• Analyze Functional Groups: Assess which functional groups are present in a compound and predict how they might react under different conditions.
• Select Appropriate Method: Choose the reduction method that complements the structure of the starting material without causing unwanted side reactions.
• Practice Deductive Reasoning: Use logical steps to match chemical compounds with the correct reduction method based on their characteristics.

Practicing with these strategies can enhance problem-solving skills and increase efficiency when tackling various chemical reduction scenarios.

Aldehydes and Ketones

Aldehydes and ketones belong to a class of organic compounds known as carbonyl compounds, characterized by the presence of a carbon-oxygen double bond (C=O). They are central to various chemical transformations due to their reactivity.

• Structure: Aldehydes have a carbonyl group attached to at least one hydrogen atom, while ketones feature a carbonyl group bonded to two carbon atoms.
• Reactivity: Both can undergo reduction to form alcohols or further to alkanes under different conditions.
• Role in Synthesis: Aldehydes and ketones are critical intermediates in organic synthesis and are used to create a wide range of products including alcohols, acids, and hydrocarbons.

Understanding the behavior of aldehydes and ketones can provide insight into which reduction method might be most appropriate for their conversion into simpler hydrocarbons.

Functional Group Reduction

Functional group reduction is a fundamental process in organic chemistry, transforming compounds by reducing the oxidation state of specific functional groups. This changes the chemical properties, creating new compounds with desired traits.

• Process: Typically involves the use of reagents that donate electrons or hydrogen to the target functional group.
• Importance: Key in converting carbonyl groups (found in aldehydes and ketones) to alkane groups, especially using reagents like Clemmensen and Wolf-Kishner.
• Applications: Widely used in pharmaceuticals, synthesis of complex molecules, and material science to fine-tune molecular characteristics.

Successfully applying reductions requires balancing the choice of method with the stability of the target compound, ensuring both efficient and selective transformations.