Question

The reaction \(\left.\left.\right|_{\text {CHO }} ^{\text {CHO }} \stackrel{\mathrm{NaOH}}{\longrightarrow}\right|_{\text {COONa }}{\text { CH }_{2} \mathrm{OH}}\) is an example of (a) intramolecular aldol condensation (b) mixed Cannizzaro reaction (c) intramolecular Cannizzaro reaction (d) crossed Cannizzaro reaction \(\Omega\)

Short answer

\(\left.\left.\right|_{\text {CHO }} ^{\text {CHO }}\stackrel{\mathrm{NaOH}}{\longrightarrow}\right|_{\text {COONa }} \text{CH}_{2} \mathrm{OH}\) a) Intramolecular aldol condensation b) Mixed Cannizzaro reaction c) Intramolecular Cannizzaro reaction d) Crossed Cannizzaro reaction Answer: c) Intramolecular Cannizzaro reaction

Step-by-step solution

Write down the given reaction

The given reaction is: \(\left.\left.\right|_{\text {CHO }} ^{\text {CHO }}\stackrel{\mathrm{NaOH}}{\longrightarrow}\right|_{\text {COONa }} \text{CH}_{2} \mathrm{OH}\)

Identify the reactant and product

In the reaction, the reactant molecule has two aldehyde groups (CHO). It reacts with sodium hydroxide (NaOH) to form a product with a carboxylate group (COONa) and a hydroxy group (CH2OH) on adjacent carbon atoms.

Determine if it is an aldol condensation

In an aldol condensation, an aldehyde or a ketone reacts with itself or another carbonyl compound in the presence of a base, leading to the formation of a β-hydroxy aldehyde or a β-hydroxy ketone. Since the product in the given reaction has a β-hydroxy group and a carboxylate group, we can conclude that this is not an example of an aldol condensation.

Determine if it is a Cannizzaro reaction

A Cannizzaro reaction is a redox reaction that involves the oxidation of an aldehyde to a carboxylic acid and the reduction of another aldehyde group to a primary alcohol in the presence of a base. Since the given reaction involves the conversion of an aldehyde group to a carboxylate group and another aldehyde group to a primary alcohol, this is an example of a Cannizzaro reaction. Now we need to determine if it is mixed, intramolecular, or crossed Cannizzaro reaction.

Identify the type of Cannizzaro reaction

- A mixed Cannizzaro reaction occurs between two different aldehydes with no alpha-hydrogen atoms. - An intramolecular Cannizzaro reaction occurs when both aldehyde groups are present in a single molecule, and the reaction takes place within the molecule. - A crossed Cannizzaro reaction occurs when two different aldehyde reactants with no alpha-hydrogen atoms are used in the reaction. In the given reaction, the aldehyde groups are present on a single molecule, and the reaction takes place within the molecule. Therefore, this is an example of an intramolecular Cannizzaro reaction. So, the correct answer is (c) intramolecular Cannizzaro reaction.

Key concepts

Cannizzaro Reaction

The Cannizzaro reaction is a unique type of redox reaction in organic chemistry. It specifically involves the conversion of an aldehyde into two different functional groups: a carboxylic acid and an alcohol. One key aspect of this reaction is that it doesn't require any hydrogen on the alpha carbon of the aldehyde. This is unlike reactions such as the aldol condensation that typically require such hydrogen.

This reaction occurs in the presence of a strong base, commonly sodium hydroxide (NaOH). The base facilitates the reaction, allowing the aldehyde to undergo disproportionation. In other words, some molecules are oxidized to carboxylates, while others are reduced to alcohols.

• In a Cannizzaro reaction, no formation of a carbon-carbon bond occurs.
• It is typically used with aldehydes that lack alpha-hydrogens. A classic example is the reaction involving formaldehyde.

This reaction can take three forms: mixed, crossed, and intramolecular. Each variety depends on the molecular interaction types between aldehydes participating in the reaction.

Aldehyde Chemistry

Aldehydes are organic compounds containing the functional group \(\text{-CHO}\). They play a significant role in many organic reactions due to their structural versatility and reactive nature. Generally, they are susceptible to nucleophilic attack due to the polar nature of the carbonyl carbon.

In their simplest form, aldehydes include formaldehyde, acetaldehyde, and benzaldehyde. Each of these has distinct properties and reactivity.

• Simple aldehydes such as formaldehyde are highly reactive and undergo polymerization easily.
• They can participate in various reactions like oxidation to carboxylic acids or reduction to alcohols.

A clear understanding of aldehyde chemistry is crucial for comprehending reactions like the Cannizzaro reaction, as these reactions highlight the dual ability of aldehydes to be oxidized and reduced.

Redox Reaction in Organic Chemistry

Redox reactions, short for reduction-oxidation reactions, play a fundamental role in organic chemistry. They involve the transfer of electrons between two species, resulting in the change of oxidation states.

In the realm of organic chemistry, redox reactions are involved in numerous processes:

• Oxidation involves the increase of the oxidation state, often seen when alcohols are converted to aldehydes and ketones.
• Reduction involves a decrease in oxidation state, typical when aldehydes are reduced to alcohols.

The Cannizzaro reaction is a perfect example of a redox process. Here, one aldehyde group is reduced to an alcohol, while another is oxidized to a carboxylic acid. It showcases both aspects of redox reactions, emphasizing the balance of electron transfer.

Organic Chemistry Reactions

Organic chemistry features a rich variety of reactions, each serving different purposes in the synthesis and transformation of organic molecules. Reactions can involve changes in bonding, structure, or functional groups and can be driven by factors such as temperature, catalysts, and chemical environment.

Common categories of organic chemistry reactions include:

• Substitution reactions, where one group replaces another on a molecule.
• Addition reactions, involving the addition of groups to unsaturated molecules.
• Elimination reactions, resulting in the loss of water or other small molecules to form double bonds.
• Rearrangement reactions, which lead to structural changes within the molecule.

The Cannizzaro reaction fits into this scheme as a redox reaction that also illustrates the concept of disproportionation. Understanding these basic types provides a foundation for mastering more complex transformations in organic synthesis.