Question

The hemiketal of acetone can be formed by adding: A. \(\mathrm{HCl}\) B. \(\mathrm{CH}_3 \mathrm{OH}\) C. \(\mathrm{NaOH}\) D. formaldehyde

Short answer

B. \( \text{CH}_3\text{OH} \)

Step-by-step solution

Identify the Functional Group of Acetone

Acetone is the simplest ketone with the chemical formula \(\text{(CH}_3\text{)}_2\text{CO}\). The carbonyl group (C=O) is the key functional group in acetone.

Understand What a Hemiketal Is

A hemiketal is formed when a ketone reacts with an alcohol (ROH). The carbonyl group (C=O) reacts with the hydroxyl group (OH) from the alcohol to form a hemiketal (a molecule with both an OH and an OR group attached to the same carbon).

Determine the Correct Reagent

To form a hemiketal, alcohol (\text{ROH}) needs to react with the ketone. Among the options given, \( \text{CH}_3\text{OH} \) is an alcohol.

Eliminate Incorrect Options

Other options provided are \( \text{HCl} \) (an acid), \( \text{NaOH} \) (a base), and formaldehyde (an aldehyde), none of which can form a hemiketal with acetone.

Choose the Correct Answer

Since \( \text{CH}_3\text{OH} \) is the only alcohol provided, it is the correct reagent to form the hemiketal of acetone.

Key concepts

Acetone Functional Group

Acetone is one of the simplest and most commonly known ketones. It has the chemical formula \(\text{(CH}_3\text{)}_2\text{CO}\). The key functional group here is the carbonyl group (C=O), where the carbon atom is double-bonded to an oxygen atom.
This carbonyl group is highly reactive and plays a vital role in many organic reactions.

• Acetone is soluble in water because of its polarity.
• It is often used as a solvent in labs and industrial processes.

Understanding the acetone functional group is critical because it dictates how acetone will react with other molecules. For example, the carbonyl group in acetone can react with different types of molecules, such as alcohols, to form compounds like hemiketals.

Hemiketal Definition

A hemiketal is a specific type of functional group that forms when a ketone reacts with an alcohol.
The reaction occurs at the carbonyl carbon (the carbon in the C=O group) and results in a molecule that has both an -OH (hydroxyl) group and -OR (alkoxy) group attached to the same carbon.

Here's how you can visualize it:

• The carbonyl carbon (C=O) reacts with the hydroxyl (-OH) group from an alcohol.
• One part of the alcohol adds directly to the carbonyl carbon.
• The oxygen in the -OH group stays attached to the carbonyl carbon, resulting in a structure with both -OH and -OR groups.

This formation is crucial in organic chemistry for understanding how ketones can be transformed into more complex molecules through reactions involving alcohols.

Reagents for Hemiketal Formation

To form a hemiketal, you need a ketone and an alcohol. In the given example, acetone serves as the ketone, and you need to identify a suitable alcohol from the provided options.
The correct choice is \(CH_3OH\), also known as methanol. Here's why:

• Methanol contains the necessary -OH group that will react with the carbonyl group in acetone.
• Other choices like \(HCl\), \(NaOH\), and formaldehyde are not suitable because they don't have the -OH group needed for this reaction.

When methanol interacts with acetone, it will attach to the carbonyl carbon, generating a hemiketal. This step is crucial for creating more complex organic molecules from simpler ones.

Organic Reaction Mechanisms

Understanding organic reaction mechanisms helps you to predict how molecules will interact during chemical reactions. In the case of forming a hemiketal, the mechanism follows these broad steps:

• The ketone (acetone) exposes its carbonyl group.
• The alcohol (methanol) provides its hydroxyl group (-OH) to interact with the carbonyl carbon.
• This interaction leads to the formation of a hemiketal with both -OH and -OR groups on the same carbon.

By understanding these steps, you can grasp how specific reagents like alcohols react with carbonyl compounds to form new functional groups.
This knowledge is fundamental in organic chemistry, helping you predict and understand the outcomes of reactions involving different functional groups.