Question

Which of the following compound has high melting point?

• A. 1-Bromopropane
• B. 1-Bromopropane
• C. 1-Bromobutane
• D. 1-Bromo-2-methylpropane

Hint:

The greater the molecular weight and the length of the carbon chain in organic molecules, the higher the melting point, due to stronger intermolecular forces.

Answer 1

The Correct Option is C

Melting Point of Organic Compounds (Haloalkanes):
Melting points are influenced by:

• Molecular Symmetry: Increased symmetry enhances crystal lattice packing, resulting in higher melting points.
• Branching: Branched isomers typically exhibit lower melting points than their unbranched counterparts.
• Molecular Weight: Higher molecular weight generally correlates with higher melting points.

Analysis of Options:

Option 1: 1-Bromopropane

• Straight-chain, small molecule. Less symmetrical compared to some alternatives.
• Expected to have a moderate melting point.

Option 2: 1-Bromopropane

• This is a duplicate of Option 1.

Option 3: 1-Bromobutane

• Possesses a longer carbon chain and greater molecular weight than bromopropane.
• However, its symmetry is limited. Its melting point is higher than propyl derivatives but not the maximum among the options.

Option 4: 1-Bromo-2-methylpropane

• Highly branched structure, leading to inefficient packing in the crystal lattice.
• Irregular molecular shape results in a lower melting point.

Key Consideration:
For haloalkanes, molecular symmetry plays a crucial role in determining melting point, often more so than molecular weight alone. The straight-chain structure of 1-Bromobutane allows for superior packing compared to branched isomers, contributing to its elevated melting point.

Conclusion: Option 3: 1-Bromobutane