Problem 55 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

Carbolic acid is: (a) \(\mathrm{C}_{6} \mathrm{H}_{3} \mathrm{CHO}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (c) \(\mathrm{C}_{\mathrm{c}} \mathrm{H}_{3} \mathrm{COOH}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{3} \mathrm{OH}\)

Step-by-Step Solution

Answer

Option (d), although inaccurately printed, represents carbolic acid – phenol.

Step 1: Understand the Chemical Composition of Carbolic Acid

Carbolic acid is another name for phenol, which is a chemical compound with the formula \(\mathrm{C}_{6} \mathrm{H}_{5}\mathrm{OH}\). It consists of a benzene ring bonded to a hydroxyl group \(\text{–OH}\).

Step 2: Analyze Each Option

Let's evaluate each of the given options:- (a) \(\mathrm{C}_{6} \mathrm{H}_{3} \mathrm{CHO}\): This is benzaldehyde, not phenol.- (b) \(\mathrm{C}_{6} \mathrm{H}_{6}\): This is benzene, without the hydroxyl group.- (c) \(\mathrm{C}_{\mathrm{c}} \mathrm{H}_{3} \mathrm{COOH}\): The formula is incomplete or not typically related to known carbolic compounds. Assuming this is an error, the closest similar formula might be for an acid like benzoic acid, which is \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\).- (d) \(\mathrm{C}_{6} \mathrm{H}_{3} \mathrm{OH}\): This option incorrectly represents phenol as it should be \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\). However, this is the closest representation to phenol when accounting for common misprints or typographical errors.

Step 3: Choose the Correct Answer

The closest correct representation for carbolic acid (phenol) among the misprinted options is (d), even though the correct chemical formula for phenol is \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\).

Key Concepts

Phenol

Phenol is an aromatic organic compound, also known colloquially as carbolic acid. Its chemical formula is \( \text{C}_6\text{H}_5\text{OH} \). This compound consists of a benzene ring attached directly to a hydroxyl group (\(\text{–OH}\)).
Phenol is a colorless or white crystalline solid that can be volatile. It is slightly soluble in water and has a distinctive sweet and tarry odor.

• Historically, phenol was first extracted from coal tar, and modern synthetic methods allow its production from benzene.
• Phenol derivatives are used as precursors to plastics and related materials.
• Due to its antiseptic properties, phenol was one of the first surgical antiseptics.

Despite its usefulness, phenol can be corrosive to human skin, and caution is advised when handling it in laboratories.

Chemical Compounds

Chemical compounds are substances composed of two or more different chemical elements bonded together. Each compound has a unique chemical formula that denotes the ratio of its constituent elements.

• Chemical bonding in compounds can occur through ionic bonds, covalent bonds, or metallic bonds.
• The chemical and physical properties of compounds are distinct and determined by their molecular structure.
• Notable examples of chemical compounds include water (\( \text{H}_2\text{O} \)), carbon dioxide (\( \text{CO}_2 \)), and phenol (\( \text{C}_6\text{H}_5\text{OH} \)).

In organic chemistry, compounds such as phenol have functional groups that define their chemical reactions and properties. For phenol, the hydroxyl group \(\text{–OH}\) is a pivotal aspect.

Benzene Ring

The benzene ring is an iconic structure in organic chemistry, composed of six carbon atoms arranged in a hexagonal ring with alternating double bonds. This structure is denoted by the chemical formula \( \text{C}_6\text{H}_6 \).
Each carbon atom in the benzene ring is covalently bonded to one hydrogen atom, allowing benzene to maintain a balanced and stable structure known as "aromaticity."
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The concept of aromaticity provides benzene with unique stability and chemical qualities.

It serves as a building block for various important chemical compounds, including phenol.

A benzene ring's structure contributes to the distinct scent associated with aromatic compounds.

Phenol's structure involves substituting one hydrogen atom in benzene with a hydroxyl group, forming a functional group attached to the aromatic ring.

Hydroxyl Group

The hydroxyl group, symbolized as \(\text{–OH}\), is a functional group consisting of an oxygen atom covalently bonded to a hydrogen atom.
In phenol, the hydroxyl group is directly attached to the benzene ring, which influences the compound's chemical properties significantly.

• The presence of the hydroxyl group makes phenol more acidic than alcohols due to resonance stabilization of the phenoxide ion.
• The hydroxyl group in organic chemistry is often involved in hydrogen bonding, affecting a molecule's boiling point and solubility.
• Understanding the behavior of hydroxyl groups helps in predicting chemical reactions, particularly in the context of alcohols and phenols.

This group plays a critical role in defining the reactivity and interactions of organic molecules like phenol.