Question

Match Column I with Column II. Column I (a) Aldol condensation (b) Cannizzaro reaction (c) Reformatsky reaction (d) Benzoin condensation Column II (p) Hydride ion transfer (q) Zinc enolate (r) \(\overline{\mathrm{C}} \mathrm{N}\) as catalyst (s) Enolate ion

Short answer

(a) -> (s), (b) -> (p), (c) -> (q), (d) -> (r)

Step-by-step solution

Understanding Aldol Condensation

Aldol condensation is an organic reaction where the enolate ion of one carbonyl compound attacks the carbonyl carbon of another. This typically produces enolate ions as intermediates. Therefore, match (a) Aldol condensation with (s) Enolate ion.

Understanding Cannizzaro Reaction

The Cannizzaro reaction involves the transfer of a hydride ion and occurs in aldehydes that do not possess alpha hydrogens. It involves intermolecular hydride transfer from one aldehyde to another. Hence, match (b) Cannizzaro reaction with (p) Hydride ion transfer.

Understanding Reformatsky Reaction

The Reformatsky reaction involves the formation of zinc enolates from alpha-halo esters and aldehydes or ketones, facilitated by zinc metal. Therefore, match (c) Reformatsky reaction with (q) Zinc enolate.

Understanding Benzoin Condensation

Benzoin condensation involves the condensation of benzaldehydes to form benzoin utilizing cyanide ion or its derivatives as catalysts, often represented as ar{C}N. So, match (d) Benzoin condensation with (r) ar{C}N as catalyst.

Key concepts

Aldol Condensation

Aldol condensation is a fundamental reaction in organic chemistry that connects smaller carbonyl compounds to form larger molecules. It involves two key steps: the formation of an enolate ion and the subsequent nucleophilic attack on another carbonyl compound. The reaction begins when a base abstracts an alpha-hydrogen from the carbonyl compound, generating an enolate ion.

This enolate ion, which is a reactive nucleophile, attacks the carbonyl carbon of another molecule. As a result, a new carbon-carbon bond is formed, leading to a β-hydroxy carbonyl compound, commonly known as an aldol. Further dehydration can occur to form an α, β-unsaturated carbonyl compound, also known as an enone, especially under acidic or heated conditions.

• The reaction often requires a base such as hydroxide or alkoxide.
• It is important in forming complex molecules in synthetic organic chemistry.

Overall, this reaction is versatile, allowing chemists to build larger, functionalized molecules from simpler ones.

Cannizzaro Reaction

The Cannizzaro reaction is unique among organic reactions, as it involves the transfer of a hydride ion between two molecules of an aldehyde that lack alpha hydrogen atoms. This reaction is notable in that it does not require any alpha hydrogen for the reaction to occur, unlike aldol condensation.

The process begins with the aldehyde being attacked by a base, leading to the formation of an alkoxide ion. This ion subsequently donates a hydride ion to another molecule of the aldehyde, which is then reduced to its corresponding alcohol. Meanwhile, the original aldehyde is oxidized to a carboxylic acid.

• Generally occurs in the presence of a strong base.
• Useful for converting simple aldehydes into useful chemical intermediates like alcohols and acids.

It provides a pathway to prepare alcohols and carboxylic acids simultaneously from aldehydes, showcasing a fascinating example of redox chemistry in organic reactions.

Reformatsky Reaction

The Reformatsky reaction involves the unique formation of zinc enolates, which are key intermediates in creating new carbon-carbon bonds. This reaction starts with the reaction of alpha-haloesters with zinc to form organozinc intermediates, otherwise known as zinc enolates.

These zinc enolates then act as nucleophiles attacking carbonyl compounds like aldehydes or ketones. This forms a beta-hydroxy ester product after protonation. The reaction is distinguished by its use of zinc, which helps in stabilizing the enolate and facilitating the nucleophilic addition.

• Useful in forming complex esters and other organic compounds.
• Conducted under mild conditions compared to other enolate reactions.

The Reformatsky reaction not only expands the toolkit of synthetic chemists but also exemplifies metal-mediated bond formation in organic synthesis.

Benzoin Condensation

Benzoin condensation is a critical reaction in forming a specific type of carbon-carbon bond between two aromatic aldehydes, typically benzaldehyde. This reaction notably employs cyanide ions, denoted as \(\overline{\text{CN}}\), or derivatives as catalysts to facilitate the reaction.

During the process, the cyanide ion attacks the carbonyl carbon of one benzaldehyde molecule, forming a cyanohydrin intermediate. This intermediate then acts as a nucleophile and attacks another carbonyl carbon of a separate benzaldehyde, linking the two molecules together to form benzoin.

• The reaction is an example of how simple molecules can be combined to form more complex structures.
• Cyanide ions are very effective in producing this reaction due to their nucleophilic properties.

The benzoin condensation remains an important industrial and laboratory-scale reaction for constructing aromatic alpha-hydroxy ketones, which are valuable in the further synthesis of other organic molecules.