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

Understanding Melting Point Trends:
The melting point of organic compounds, especially haloalkanes, depends on several factors:
  • Molecular symmetry: More symmetrical molecules pack better in the crystal lattice, leading to higher melting points.
  • Branching: Branched isomers usually have lower melting points than their straight-chain counterparts.
  • Molecular weight: Heavier molecules generally have higher melting points.

Now, let's evaluate the options:

Option 1: 1-Bromopropane
  - Straight chain, small size. Less symmetrical than some other options.
  - Moderate melting point.

Option 2: 1-Bromopropane
  - Repetition of Option 1.

Option 3: 1-Bromobutane
  - Longer chain than bromopropane, higher molecular weight.
  - But it's still not very symmetrical. Melting point is higher than propyl derivatives but not the highest.

Option 4: 1-Bromo-2-methylpropane
  - Highly branched, hence poor packing.
  - Lower melting point due to irregular shape.

Important Insight:
Among haloalkanes, the most symmetrical structure contributes significantly to a higher melting point — not just molecular weight.
1-Bromobutane, being the longest straight-chain molecule among the options, offers better packing than branched isomers and thus has a higher melting point.

Final Answer: Option 3: 1-Bromobutane