Question

Aldehydes are readily oxidized to yield carboxylic acids, but ketones are inert to oxidation. Which is the most likely explanation regarding this difference in reactivity? A. Aldehydes have a proton attached to the carbonyl that is abstracted during oxidation. Ketones lack this proton and so cannot be oxidized. B. Reducing agents like \(\mathrm{HNO}_3\) are sterically hindered by ketone's carbonyl carbon. C. Aldehydes and ketones are of similar hybridization. D. The rate of the forward oxidation reaction is equal to the rate of the reverse redaction reaction in ketones.

Short answer

Option A is the correct answer.

Step-by-step solution

- Understand the Reactivity of Aldehydes

Aldehydes contain a carbonyl group where the carbon atom is bonded to a hydrogen atom and an R group. The hydrogen attached to the carbonyl carbon can be abstracted via oxidation, turning the aldehyde into a carboxylic acid.

- Recognize the Stability of Ketones

In ketones, the carbonyl group is flanked by two R groups. Unlike aldehydes, ketones do not have a hydrogen atom attached to the carbonyl carbon. This means there is no hydrogen to be abstracted, making ketones less reactive to oxidation compared to aldehydes.

- Evaluate Each Option

A. This option is correct as it highlights the presence of a hydrogen in aldehydes that can be abstracted during oxidation.B. This option is incorrect as steric hindrance due to the carbonyl group is not the main reason.C. Hybridization is similar but it does not explain the reactivity difference.D. The rate of the reverse reaction in ketones does not explain their resistance to oxidation.

- Conclude the Answer

Option A offers the most likely explanation since aldehydes have a proton attached to the carbonyl carbon that can be abstracted during oxidation, whereas ketones lack this proton.

Key concepts

carbonyl reactivity

Aldehydes and ketones both contain the carbonyl group (C=O), which is highly reactive. However, the reactivity of these groups differs because of their structures. Aldehydes have a carbonyl carbon bonded to a hydrogen atom, while ketones have the carbonyl carbon bonded to two R groups. This difference greatly impacts their reactivity.

In aldehydes, the hydrogen atom attached to the carbonyl carbon can be easily abstracted, making them more reactive, especially in oxidation reactions. On the other hand, the lack of this hydrogen in ketones makes them less reactive.

The key points to understand are:

• Aldehydes' structure leads to high reactivity due to the presence of the hydrogen atom.
• Ketones lack this hydrogen, making them less prone to oxidation.

oxidation mechanisms

Oxidation involves the increase in oxidation state of a molecule, atom, or ion. For aldehydes, the oxidation process typically converts the aldehyde group to a carboxylic acid. Here's how it works:

• The hydrogen atom on the aldehyde's carbonyl carbon is removed (abstracted).
• This results in the formation of a carboxylic acid (R-COOH).


For ketones, no hydrogen is present on the carbonyl carbon. Therefore, oxidation in the same manner as aldehydes cannot occur.

To summarize:

• Aldehydes can be oxidized to carboxylic acids because of the presence of hydrogen on the carbonyl carbon.
• Ketones cannot undergo the same oxidation due to the lack of hydrogen.

organic chemistry principles

Understanding the principles of organic chemistry is crucial when analyzing the differences in reactivity between aldehydes and ketones.

Some fundamental principles include:

• Functional Groups: The carbonyl group (C=O) is a significant functional group in aldehydes and ketones.
• Electronegativity: Oxygen’s high electronegativity causes partial positive and negative charges.
• Steric Hindrance: The spatial arrangement around the carbonyl carbon can significantly impact reactivity.


Applying these principles, we see:

• The partial positive charge on carbonyl carbon makes aldehydes more reactive than ketones.
• Ketones have more steric hindrance due to two R groups, reducing reactivity compared to aldehydes.