Question

Wolff-Kishner reduction of benzophenone gives (a) benzene (b) toluene (c) diphenylmethane (d) ethylbenzene

Short answer

Answer: The product formed when benzophenone undergoes Wolff-Kishner reduction is diphenylmethane.

Step-by-step solution

Identify the starting compound

The starting compound is benzophenone, which has a carbonyl group and two phenyl groups, as shown below: Benzophenone: C6H5C(O)C6H5

Understand the Wolff-Kishner reduction reaction mechanism

The Wolff-Kishner reduction involves treating the carbonyl compound with hydrazine (N2H4) and a strong base. This reaction converts the carbonyl group into a methylene group (-CH2-). The overall reaction mechanism is as follows: 1. Formation of the hydrazone: The carbonyl compound reacts with hydrazine to form a hydrazone derivative. 2. Formation of the nitrogen anion: The strong base deprotonates the hydrazone, which then eliminates the dinitrogen (N2) molecule to form the nitrogen anion. 3. Formation of the final reduced product: The nitrogen anion acts as a nucleophile and attacks one of the phenyl groups, resulting in the formation of a methylene group in between the two phenyl groups.

Determine the product based on the reaction mechanism

Applying the Wolff-Kishner reaction mechanism to benzophenone, the carbonyl group is reduced to a methylene group and the molecule becomes: Diphenylmethane: C6H5CH2C6H5 Now, we can match this product with the given options.

Choose the correct option

Comparing the product obtained in step 3 with the given options, we find that the correct option is: (c) diphenylmethane

Key concepts

Benzophenone

Benzophenone is an organic compound commonly used in various chemical reactions. It consists of a carbonyl group (C=O) flanked by two phenyl groups (C6H5). This makes it a part of the ketone family in organic chemistry. Because of its structure, benzophenone is reactive and can undergo reduction, turning the carbonyl group into a functional group with fewer oxygen atoms.
Benzophenone is also a popular starting material in synthesis due to its robust aromatic rings and carbonyl reactivity. These properties make it a good candidate for various reduction reactions, such as the Wolff-Kishner reduction, which eliminates the carbonyl group entirely.

Reduction Reactions

Reduction reactions are processes in chemistry where a molecule gains electrons, often reducing the number of oxygen atoms. In organic chemistry, this typically involves transforming a carbon-oxygen bond into a carbon-hydrogen bond.
The Wolff-Kishner reduction is a specific type of reduction reaction that targets carbonyl groups (like those in ketones and aldehydes). By replacing the oxygen in the carbonyl group with hydrogen atoms, the reaction effectively transforms the group into a methylene unit (-CH2-). This kind of reaction is key to modifying chemical structures in organic synthesis, allowing for the alteration of molecules' properties and functions.

Organic Chemistry

Organic chemistry is the study of carbon-containing compounds, their properties, reactions, and structures. It is a vast field that encompasses everything from simple molecules like methane to complex polymers and biomolecules.
Within organic chemistry, understanding reaction mechanisms is critical. Mechanisms give insight into how and why reactions proceed in specific ways. The transformation of benzophenone through reduction reactions like Wolff-Kishner is an excellent example of applying mechanistic understanding to achieve desired chemical changes. It demonstrates the intricacy of manipulating molecular structures to produce new compounds.

Reaction Mechanism

The reaction mechanism is a detailed step-by-step account of the transformation from reactants to products. For the Wolff-Kishner reduction, the mechanism begins with the formation of a hydrazone from a carbonyl group and hydrazine.

• First, hydrazine reacts with the carbonyl group to form a hydrazone.
• Next, a strong base helps to eliminate nitrogen gas (N2), converting the hydrazone into a nitrogen anion.
• Finally, this anion facilitates further changes, ultimately replacing the carbonyl group with a methylene group.

This multi-step process also highlights vital concepts like nucleophilicity and stable intermediate states. Understanding the detailed steps of reaction mechanisms helps chemists predict and control the outcomes of chemical reactions, ensuring the successful formation of target products like diphenylmethane from benzophenone.