Question

Dimerisation of solute molecules in low dielectric constant solvent is due to :

• A. Hydrogen bond
• B. Covalent bond
• C. Co-ordinate bond
• D. Ionic bond

Answer 1

The Correct Option is A

Dimerisation of solute molecules in solvents with a low dielectric constant occurs predominantly due to hydrogen bonding.

Detailed Explanation: 

• (A) Hydrogen bond: Correct Answer. In solvents with low dielectric constants, intermolecular hydrogen bonds become stronger due to the reduced solvent polarity, leading to the formation of stable dimers. This phenomenon is typical in carboxylic acids (e.g., acetic acid dimerisation in benzene).
• (B) Covalent bond: Incorrect. Covalent bonds involve electron sharing within molecules, not between distinct molecules in solution under these conditions.
• (C) Co-ordinate bond: Incorrect. Coordinate bonds involve electron donation from one species to another, usually seen in complex formation, not typical for dimerisation in low dielectric solvents.
• (D) Ionic bond: Incorrect. Ionic bonds generally require solvents with high dielectric constants (like water) for ion stabilization and dissociation. They are not favored in solvents with low dielectric constants.

Conclusion:

The correct answer is Option (A): Hydrogen bond.

Answer 2

In solvents with low dielectric constants, the solute molecules tend to form dimers through **hydrogen bonding**. Hydrogen bonds are attractive forces that occur between hydrogen atoms and electronegative atoms like oxygen or nitrogen. In solvents with low dielectric constants, the solvent's ability to dissociate ions or solvate molecules is limited, making intermolecular forces like hydrogen bonding more significant in promoting dimer formation.

Hydrogen bonds can lead to the dimerisation of molecules by forming bonds between hydrogen atoms attached to electronegative atoms (like O-H or N-H) and lone pairs of electrons on other electronegative atoms (such as O or N).
- Other types of bonds such as covalent, co-ordinate, and ionic bonds do not generally lead to dimerisation in low dielectric solvents in the same way as hydrogen bonds do.

Thus, the correct answer is hydrogen bond.