Arrange the following alkyl halides in increasing order of boiling points
(A) 1-lodobutane
(B) 1-Bromobutane
(C) 1-Chlorobutane
(D) Butane
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (D), (C), (B), (A)
Boiling points of these compounds increase with increasing molecular weight (molar mass) because stronger van der Waals forces require more energy to overcome. All are non-polar or nearly non-polar molecules of similar shape (straight chain), so polarity differences are negligible compared to mass.
Molar masses:
- (D) Butane (C₄H₁₀): 58 g/mol
- (C) 1-Chlorobutane (C₄H₉Cl): 92.5 g/mol
- (B) 1-Bromobutane (C₄H₉Br): 137 g/mol
- (A) 1-Iodobutane (C₄H₉I): 184 g/mol
Thus, increasing order of boiling points: Butane < 1-Chlorobutane < 1-Bromobutane < 1-Iodobutane, i.e., (D) < (C) < (B) < (A).
Actual approximate boiling points confirm this:
- Butane: −0.5 °C
- 1-Chlorobutane: 78 °C
- 1-Bromobutane: 101 °C
- 1-Iodobutane: 130 °C