Problem 22 - Chemistry in 30 days

Question

When \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{COOH}\) is reduced with LiAIH \(_{4}\), the compound obtained will be (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHO}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (d) \(\mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{OH}\)

Step-by-Step Solution

Answer

The compound obtained is (d) \( \mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{OH} \).

Step 1: Identify the functional group

The compound given is a carboxylic acid, \( ext{CH}_2= ext{CH}- ext{COOH}\). The functional group present is the carboxylic acid group \(- ext{COOH}\).

Step 2: Recognize the reducing agent and its action

LiAlHt{4} is a strong reducing agent, commonly used to reduce carboxylic acids (\(- ext{COOH}\)) to primary alcohols (\(- ext{CH}_2 ext{OH}\)). It reduces the carboxylic acid completely to an alcohol.

Step 3: Predict the product after reduction

Upon reduction of \( ext{CH}_2= ext{CH}- ext{COOH}\) using \( ext{LiAlH}_4\), the carboxylic acid group \(- ext{COOH}\) is converted to \(- ext{CH}_2 ext{OH}\), resulting in the compound \( ext{CH}_2= ext{CH}- ext{CH}_2 ext{OH}\).

Step 4: Match the product with the options

The product \( ext{CH}_2= ext{CH}- ext{CH}_2 ext{OH}\) matches option (d): \( ext{CH}_2= ext{CHCH}_2 ext{OH}\).

Key Concepts

Carboxylic Acid Reduction

Carboxylic acids are compounds that contain the functional group \(-COOH\). In organic chemistry, reducing a carboxylic acid involves converting this group into a different functional group, typically converting it into an alcohol through a process called reduction.
During reduction, the carboxylic acid is transformed into an alcohol, which is a simpler functional group. Carboxylic acid reduction is valuable in various chemical syntheses, where converting a \(-COOH\) into \(-CH_2OH\) can change the compound's physical and chemical properties. Reducing agents like \( ext{LiAlH}_4\) are often used as they can effectively facilitate this transformation.

LiAlH4 reducing agent

Lithium aluminium hydride, \(\text{LiAlH}_4\), is a strong reducing agent often employed in organic chemistry for reducing certain types of functional groups. It has the capability to reduce carboxylic acids to primary alcohols efficiently.
\(\text{LiAlH}_4\) is preferred due to its powerful reductive capabilities, though care must be taken in its use because it reacts violently with water. When utilized in reduction reactions, \(\text{LiAlH}_4\) transfers hydrogen atoms to the substrate, effectively breaking down the more complex carboxylic acid structure and converting it into an alcohol.

Functional Groups

Functional groups are specific groupings of atoms within molecules that determine the characteristic reactions of those molecules. In organic chemistry, recognizing and understanding functional groups helps to predict how compounds will behave.
Among the common functional groups are carboxylic acids \(-COOH\) and alcohols \(-OH\). The functional group in the original compound, \(\text{CH}_2=\text{CH}-\text{COOH}\), is the carboxylic acid. \(\text{LiAlH}_4\) changes this functional group to an alcohol in the reduction process, converting \(-COOH\) to \(-CH_2OH\), resulting in the formation of \(\text{CH}_2=\text{CH}-\text{CH}_2OH\).

Alcohol Formation

Alcohol formation is the process by which certain functional groups in a molecule are converted into an alcohol group. In the context of the exercise, the reduction of carboxylic acid using \ ext{LiAlH}_4\ is a typical example.
This transformation involves the carbon of the \(-COOH\) group gaining hydrogen atoms while the oxygen double bond is reduced to a single bond, forming \(-CH_2OH\). The resulting alcohol, \(\text{CH}_2=\text{CH}-\text{CH}_2OH\), maintains the carbon framework of the original molecule, while gaining new properties characteristic of alcohols, such as increased solubility in water and reactivity toward specific types of chemical reactions.