Question

If cinnamaldehyde was treated with LiAlH \(_{4}\), what reaction would occur? (A) Reduction, resulting in a primary alcohol (B) Oxidation, resulting in a carboxylic acid (C) An acid–base reaction, resulting in a diol (D) No reaction would occur.

Short answer

(A) Reduction, resulting in a primary alcohol

Step-by-step solution

- Identify the reactants and reagents

Cinnamaldehyde is the starting compound, and LiAlH _4 is the reducing agent. LiAlH _4 is commonly used to reduce aldehydes, ketones, and other carbonyl-containing compounds.

- Understand the functional group in cinnamaldehyde

Cinnamaldehyde contains an aldehyde functional group (—CHO) along with an aromatic benzene ring. The aldehyde group is reactive to reduction.

- Determine the reaction type with LiAlH_4

LiAlH_4 is a strong reducing agent. When it reacts with an aldehyde, it typically reduces the aldehyde to a primary alcohol. The reduction involves the addition of hydrogen to the carbonyl carbon.

- Predict the product

When cinnamaldehyde reacts with LiAlH_4, the aldehyde group (—CHO) is reduced to a primary alcohol (—CH_2OH). The benzene ring remains unchanged.

- Choose the correct answer

Given the product is a primary alcohol, the reaction is a reduction. Therefore, the correct answer is (A) Reduction, resulting in a primary alcohol.

Key concepts

Reduction Reactions

Reduction reactions are a powerful and essential part of organic chemistry. These reactions involve the gain of electrons by a molecule, often achieved by adding hydrogen atoms or removing oxygen atoms from the target compound. Reducing agents, such as lithium aluminum hydride (LiAlH₄), play a key role in facilitating these reactions.

LiAlH₄ is a strong reducing agent commonly used to reduce various carbonyl-containing compounds, including aldehydes, ketones, esters, and carboxylic acids. During the reduction process, LiAlH₄ donates hydride ions (H⁻) that bond with the carbon atoms in the target functional group. This effectively lowers the oxidation state of the carbon, transforming the compound into a more reduced form.
It's important to remember that different reducing agents have different strengths and specificities. For example:

• LiAlH₄ (Lithium Aluminum Hydride) - Very strong, reduces aldehydes, ketones, esters, and carboxylic acids
• NaBH₄ (Sodium Borohydride) - Milder, typically used for reducing aldehydes and ketones

Reduction reactions are crucial for synthesizing diverse organic compounds, making them invaluable in both laboratory research and industrial applications.

Aldehyde Functional Group

Understanding aldehyde functional groups is fundamental for mastering many organic reactions. Aldehydes are organic compounds that feature a carbonyl center (C=O) bonded to a hydrogen atom and an R group (alkyl or aryl group). The general structure of an aldehyde is represented as R-CHO.

The carbonyl carbon in aldehydes is highly reactive, making aldehydes prone to various chemical transformations, including:

• Oxidation to carboxylic acids
• Reduction to primary alcohols
• Nucleophilic addition reactions

In cinnamaldehyde, the aldehyde group is connected to a benzene ring and a double bond, enhancing its reactivity. When aldehydes react with strong reducing agents like LiAlH₄, the carbonyl carbon undergoes reduction. During this reaction, the aldehyde (R-CHO) is converted into a primary alcohol (R-CH₂OH). This change is crucial in synthetic organic chemistry because primary alcohols serve as important intermediates for further chemical reactions and drug synthesis.

Primary Alcohol Synthesis

Reducing aldehydes to primary alcohols is a widely-used and vital process in organic synthesis. Primary alcohols contain a hydroxyl group (—OH) bonded to a carbon atom that is connected to only one other carbon (or hydrogen) atom. The transformation from an aldehyde to a primary alcohol typically involves a two-step mechanism facilitated by a reducing agent like LiAlH₄.

Here's a brief rundown of the typical steps in the reduction of an aldehyde to a primary alcohol:

• 1. The aldehyde's carbonyl carbon is targeted by a hydride ion (H⁻) from the reducing agent.
• 2. The carbonyl oxygen is subsequently protonated (by water or another source) to form the hydroxyl group (—OH).

In the case of cinnamaldehyde, the reduction with LiAlH₄ focuses on the aldehyde group (—CHO), converting it to a primary alcohol group (—CH₂OH) while leaving the benzene ring intact. The resulting compound has valuable applications in flavorings, perfumes, and as intermediates in pharmaceuticals.
Synthesizing primary alcohols from aldehydes is not just limited to laboratory settings. This process is fundamental in industrial chemistry and biochemistry, enabling the creation of essential chemicals used in everyday products.