Problem 32 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is oxidized to the corresponding carbonyl compound? (a) o-nitrophenol (b) 2 -hydroxypropane (c) 2 -methyl-2-hydroxypropane (d) phenol

Step-by-Step Solution

Answer

2-hydroxypropane (b) is oxidized to the corresponding carbonyl compound.

Step 1: Understand Oxidation

Oxidation in organic chemistry often involves the increase in the number of bonds to oxygen (commonly forming a carbonyl group) or the loss of hydrogen atoms. Look for functional groups that can be oxidized to a carbonyl compound (aldehyde or ketone).

Step 2: Analyze Each Option

Examine each option to determine if it contains a functional group that can be oxidized to form a carbonyl group. Options with hydroxyl groups attached to carbon atoms are candidates for oxidation to carbonyls.

Step 3: Evaluate o-Nitrophenol

o-Nitrophenol is a phenol with a nitro group in the ortho position. The hydroxyl group in phenols is generally resistant to oxidation to a carbonyl compound because the aromatic ring stabilizes it.

Step 4: Evaluate 2-Hydroxypropane

2-Hydroxypropane (also known as isopropanol or isopropyl alcohol) is a secondary alcohol. Secondary alcohols are commonly oxidized to form ketones, which are carbonyl compounds.

Step 5: Evaluate 2-Methyl-2-Hydroxypropane

2-Methyl-2-hydroxypropane (or tert-butanol) is a tertiary alcohol. Tertiary alcohols are generally resistant to oxidation to carbonyl compounds since they require the removal of a C–C bond, which is challenging.

Step 6: Evaluate Phenol

Phenol itself, like o-nitrophenol, is a hydroxyl group directly attached to an aromatic ring. This structural feature makes phenols less reactive towards oxidation to carbonyl compounds.

Step 7: Determine the Correct Answer

Among all the options, only 2-hydroxypropane can be oxidized to form a carbonyl group (acetone) as it is a secondary alcohol. The other compounds are not suitable for oxidation to carbonyl compounds.

Key Concepts

Carbonyl Compounds

In organic chemistry, carbonyl compounds play a crucial role and are characterized by a carbon atom double-bonded to an oxygen atom. This structure is known as a carbonyl group. Common examples include aldehydes and ketones. These are highly reactive and versatile functional groups, central to many chemical reactions.
Carbonyl compounds are significant because they are intermediates in numerous organic transformations. This makes them essential in producing various products, from simple commercial products to complex pharmaceutical drugs.

• Aldehydes: These contain the carbonyl group at the end of the carbon chain, bonded to at least one hydrogen atom.
• Ketones: These have the carbonyl group situated between two carbon atoms, somewhere along the carbon chain.

Understanding carbonyl compounds is key as they exhibit distinct reactivity patterns, which is vital for both synthetic and analytical chemistry.

Secondary Alcohols

Secondary alcohols are a type of alcohol where the hydroxyl group (-OH) is attached to a secondary carbon atom. This means the carbon with the hydroxyl group is connected to two other carbon atoms. A characteristic feature of secondary alcohols is their ability to be oxidized to form ketones, which are carbonyl compounds.
One common example is 2-hydroxypropane, or isopropyl alcohol, which can be oxidized to produce acetone. Oxidation of secondary alcohols involves the loss of hydrogen atoms from the carbon bonded to the hydroxyl group, forming a double-bonded oxygen in its place.

• The oxidation process can be represented as:
  Secondary alcohol (e.g., R₂CHOH) → Ketone (e.g., R₂C=O)

Understanding the behavior of secondary alcohols in oxidation reactions is important for predicting chemical transformations and is widely used in industrial and laboratory processes.

Phenols

Phenols are a unique class of aromatic compounds characterized by a hydroxyl group (-OH) directly bonded to an aromatic benzene ring. Unlike alcohols, phenols exhibit different reactivity due to the influence of the aromatic ring.
Phenols are less reactive in typical oxidation scenarios that convert alcohols into carbonyl compounds. The aromatic ring's stability offers resistance to transformation into carbonyl derivatives because the aromatic system tends to maintain its structure.

• Phenols usually undergo oxidation to quinones rather than carbonyl compounds.
• The presence of substituents like nitro groups can further influence reactivity, as seen in o-nitrophenol.

Understanding phenols' stability and reactivity is important for applications involving antioxidants and synthetic polymers.

Functional Groups in Organic Chemistry

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In organic chemistry, recognizing these functional groups is crucial. They determine how a molecule behaves and reacts during chemical processes.
Some common organic functional groups include:

• Hydroxyl (-OH): Present in alcohols and phenols, this group affects solubility and reactivity.
• Carbonyl (C=O): Present in aldehydes and ketones, known for their reactivity.

The ability to identify and understand how these functional groups interact helps chemists predict reaction outcomes. Recognizing these groups enables effective planning for syntheses and modifications in organic compounds.