Question

STATEMENT-1: \(\quad p\) -Hydroxybenzoic acid has a lower boiling point than \(o\) -hydroxybenzoic acid. because STATEMENT-2: o-Hydroxybenzoic acid has intramolecular hydrogen bonding. (A) Statement-1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement-1 (B) Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1 (C) Statement-1 is True, Statement-2 is False (D) Statement- 1 is False, Statement- 2 is True

Short answer

(A) Statement-1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement-1

Step-by-step solution

Examine Statement-1

Analyze the statement that p-Hydroxybenzoic acid has a lower boiling point than o-Hydroxybenzoic acid. By considering the general trends in boiling points, substances that cannot form intermolecular hydrogen bonds tend to have lower boiling points than similar molecules that can.

Examine Statement-2

Consider the statement that o-Hydroxybenzoic acid has intramolecular hydrogen bonding. Intramolecular hydrogen bonding within a molecule would typically reduce the ability for intermolecular hydrogen bonding, which is important for higher boiling points.

Relate Both Statements

Determine if Statement-2 explains Statement-1. Since intramolecular hydrogen bonding in o-Hydroxybenzoic acid reduces its capability to form intermolecular bonds, molecules would have a harder time sticking together, potentially lowering the boiling point compared to substances that can freely form intermolecular bonds.

Choose the Correct Option

Based on the analysis, agree with statement 1, confirm the truth of statement 2, and assess if statement 2 provides a valid explanation for statement 1, which it does because the intramolecular hydrogen bonding prevents more extensive, stronger intermolecular bonding.

Key concepts

Intramolecular Hydrogen Bonding

Understanding intramolecular hydrogen bonding is essential when analyzing organic compounds. This phenomenon occurs when a hydrogen atom, covalently bonded to a highly electronegative atom like oxygen or nitrogen within a molecule, also associates with another electronegative atom within the same molecule. This leads to an attractively stable ring of atoms.

For instance, in o-Hydroxybenzoic acid, the proximity of the hydroxyl group (-OH) to the carboxylic acid group (COOH) allows a hydrogen bond to form within the molecule itself. This bonding affects the molecule's properties including, as in the case given in the exercise, its boiling point. Since the intramolecular hydrogen bonding holds part of the molecule tightly together, there's a decreased number of hydrogen bonds between different molecules, which can reduce the overall boiling point.

Boiling Point Trends in Organic Compounds

The boiling point of an organic compound is indicative of the strength of the intermolecular forces between its molecules. Generally, stronger intermolecular attractions correspond to higher boiling points.

For organic acids and similar compounds, any feature that enhances intermolecular hydrogen bonding tends to increase their boiling point. p-Hydroxybenzoic acid doesn't have intramolecular hydrogen bonding and thus can participate more freely in intermolecular bonding. This, in turn, leads to a higher boiling point in comparison to o-Hydroxybenzoic acid, where intramolecular forces dominate. This trend underscores the concept that the availability for forming intermolecular bonds can be a significant factor in determining the boiling points of closely related compounds.

Intermolecular vs Intramolecular Forces

It is critical to differentiate between intermolecular and intramolecular forces when discussing chemical properties and the behavior of substances. Intermolecular forces are the attractions between different molecules; these include hydrogen bonds, dipole-dipole interactions, and London dispersion forces, with hydrogen bonding being particularly strong among them.

In contrast, intramolecular forces are the forces that hold a molecule together, such as covalent bonds and, in some cases, intramolecular hydrogen bonds. While intramolecular forces define a molecule's shape and stability, intermolecular forces are responsible for the physical properties observed in bulk material, like melting and boiling points. The interplay between these forces influences substance characteristics profoundly, as evidenced in the behavior of various organic compounds when comparing their boiling points and solubility.

Physical Properties of Organic Acids

The physical properties of organic acids, including their melting and boiling points, solubility, and acidity, can be heavily influenced by the presence of hydrogen bonding. Acids containing more hydroxyl or carbonyl groups typically can form more hydrogen bonds, leading to higher boiling points and greater solubility in water.

p-Hydroxybenzoic acid, lacking intramolecular hydrogen bonding, is a prime candidate for strong intermolecular bonding, which contributes to its relatively higher boiling point. Understanding the kind of hydrogen bonding present in organic acids, along with their molecular structure, is crucial for predicting and rationalizing their physical properties and behavior.