Problem 88 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

The functional group present in cresol is: [BHU 1996] (a) alcoholic - OH (b) phenolic \(-\mathrm{OH}\) (c) carbonyl \(>\mathrm{C}=\mathrm{O}\) (d) carboxylic \(-\mathrm{COOH}\)

Step-by-Step Solution

Answer

Cresol contains a phenolic -OH group.

Step 1: Identify the Structure of Cresol

Cresol is an organic compound and comes in three isomers: ortho-cresol, meta-cresol, and para-cresol. All cresols have a benzene ring with a single methyl group (\(-\mathrm{CH}_3\)) and a hydroxyl group attached to it.

Step 2: Determine the Functional Group in Cresol

Cresol contains a hydroxyl group (\(-\mathrm{OH}\)) directly attached to the benzene ring. This specific arrangement classifies the hydroxyl group as a phenolic functional group when it is directly bonded to an aromatic ring.

Step 3: Compare with Given Options

The options given are: (a) alcoholic -OH, (b) phenolic -OH, (c) carbonyl >C=O, and (d) carboxylic -COOH. Based on the identification in Step 2, the correct option that describes the -OH in cresol is option (b), phenolic -OH.

Key Concepts

Cresol Isomers

Cresol is a fascinating chemical compound found in several forms known as isomers. These isomers are structural variations of a molecule that have the same molecular formula but differ in their connectivity or arrangement of atoms. Cresol isomers specifically refer to ortho-cresol, meta-cresol, and para-cresol.

Each of these isomers has a benzene ring as its backbone, which is a common feature in organic chemistry, particularly in aromatic compounds.

In all three isomers, there is a single methyl group (\(-\mathrm{CH}_3\)) and a hydroxyl group (\(-\mathrm{OH}\)) attached to the benzene ring. The only difference between the isomers is the position of these groups on the benzene ring:

• Ortho-cresol: The methyl and hydroxyl groups are adjacent to each other.
• Meta-cresol: They are separated by one carbon atom.
• Para-cresol: They are positioned opposite to each other on the ring.

These structural differences are crucial because they can alter the chemical and physical properties of each cresol, affecting their uses and behavior in reactions.

Phenolic Compounds

Phenolic compounds are a unique class of organic molecules that feature a hydroxyl group bonded directly to an aromatic hydrocarbon group, such as a benzene ring.

This structural configuration is significant because it imparts particular properties to the molecule.

The term 'phenolic' is derived from phenol, which is the simplest compound containing a phenolic group. Cresol, like phenol, is classified as a phenolic compound due to the presence of the hydroxyl group attached to its aromatic ring. This distinguishing feature offers stability and specific reactivity that is characteristic of phenolic compounds.

These compounds are often noted for their ability to act as antioxidants and are common in various naturally occurring substances. Examples of their utility include applications in food preservation, medicines like aspirin, and disinfectants. For cresol, the phenolic -OH group plays a pivotal role in its chemical behavior, such as its acidity and ability to form hydrogen bonds.

Structural Identification

The structural identification of a molecule is a fundamental aspect of understanding its chemistry, particularly in organic chemistry. A clear identification involves recognizing the molecular formula and deducing how the atoms are arranged in the molecule.

Cresol's structural identification depends on pinpointing the position of its functional groups. The presence of the benzene ring combined with specific attachments—a methyl and a hydroxyl group—defines cresol's structure as an aromatic and phenolic compound.

Understanding the structure allows chemists to predict its reactivity, properties, and uses. For instance, by identifying the position of the -OH group in cresol, scientists can determine that it is indeed a phenolic compound, ruling out other functional group possibilities like carbonyl or carboxylic groups.

Structural identification is essential in exercises, like deciding whether the -OH group is phenolic or alcoholic, to guide accurate chemical classification. This process aids in choosing appropriate reactions to synthesize, modify, or analyze the compounds, making structural identification a cornerstone of chemical education and research.