Question

Nitration of resorcinol and catechol maximum lowers their boiling point if nitration is carried out at position respectively (A) \(\mathrm{C}-2, \mathrm{C}-2\) (B) C-2, C-3 (C) C-3, C-2 (D) C-4, C-3

Short answer

The nitration of resorcinol should be carried out at position C-2 to maximally lower its boiling point, while for catechol, the nitration should occur at position C-3 for the same effect. Therefore, the correct answer is (B) C-2, C-3.

Step-by-step solution

Structure of Resorcinol and Catechol

Resorcinol has a benzene ring with two hydroxyl groups at positions 1 and 3. Its molecular formula is C₆H₄(OH)₂. Catechol also has a benzene ring, and it has two hydroxyl groups at positions 1 and 2. Its molecular formula is C₆H₄(OH)₂. Now let's analyze the nitration of both compounds.

Nitration of Resorcinol

Whenever nitration occurs on a benzene ring, it happens on the carbon adjacent to the -OH group. In the case of resorcinol, we have -OH groups at positions 1 and 3, so nitration is more likely to occur at position 2 (C-2). This nitration will lower the boiling point of resorcinol, as the nitro group will be adjacent to the hydroxyl groups.

Nitration of Catechol

For catechol, the -OH groups are at positions 1 and 2. The nitration is more likely to take place at position 3 (C-3) in Catechol, as this position is adjacent to both hydroxyl groups. By introducing the nitro group at this position, the boiling point of catechol will be lowered.

Identifying the Correct Answer

Now that we have analyzed the nitration of resorcinol and catechol, we can conclude that for resorcinol, the nitration should occur at position C-2, while for catechol, the nitration should be carried out at position C-3 to maximally lower their boiling points. Hence, the correct answer is: (B) C-2, C-3.

Key concepts

Resorcinol

Resorcinol is a chemical compound that belongs to the family of aromatic diols. It consists of a benzene ring with two hydroxyl (\( -OH \)) groups attached at positions 1 and 3. This setup not only determines its chemical behavior but also contributes to its physical properties such as solubility and melting point. Resorcinol is often used in pharmaceuticals and as a chemical intermediate.
When it comes to nitration, the presence of hydroxyl groups on the benzene ring enhances electrophilic substitution reactions. Nitration typically occurs at the ortho or para positions relative to the \( -OH \)group. Therefore, in resorcinol, nitration is most favored at carbon-2 (C-2) since it is ortho to both hydroxyl groups. This introduces a nitro (\( -NO_2 \))group, which can affect properties like boiling point by disrupting intermolecular forces. This is because nitro groups are more likely to form hydrogen bonds with neighboring molecules, leading to changes in physical properties.

Catechol

Catechol, which is also known as 1,2-dihydroxybenzene, features a benzene ring with two hydroxyl groups at positions 1 and 2. This isomeric configuration gives catechol unique chemical properties including reactivity and the ability to form strong hydrogen bonds.
Similar to resorcinol, catechol undergoes nitration reactions where the fidelity of hydroxyl groups promotes substitution reactions. In catechol, the most susceptible site for nitration is the third carbon (C-3) because it is adjacent to both hydroxyl groups. When a nitro group is added to catechol at this position, it can significantly lower the boiling point. This effect is due to the new arrangement of molecules, which interferes with the molecule’s ability to form stable intermolecular interactions.

Boiling Point

The boiling point of a substance is determined by the strength of intermolecular forces between its molecules. Generally, the stronger these forces, the higher the boiling point.
For compounds like resorcinol and catechol, intermolecular forces are primarily influenced by hydrogen bonding due to the presence of hydroxyl groups. Nitration, which introduces a nitro group such as \(-NO_2\), can decrease the boiling point by altering these forces. The \(-NO_2\)group may produce steric hindrance or disrupt existing hydrogen bonds, resulting in less effective intermolecular interactions.
Understanding how nitration affects boiling points can help in predicting the behavior of similar aromatic compounds in different environments. This knowledge is valuable not just in academic settings but also in various industrial processes.