Question

Arrange the following compounds in decreasing order of their boiling points:

Bromo methane ${\mathrm{CH}}_3\mathrm{Br}$, Bromo ethane ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Br}$, Bromo propane ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{Br}$ and Bromo butane ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{Br}$

• A. $\mathrm{Bromomethane}>\mathrm{Bromoethane}>\mathrm{Bromopropane}>\mathrm{Bromobutane}$
• B. $\mathrm{Bromobutane}>\mathrm{Bromopropane}>\mathrm{Bromomethane}>\mathrm{Bromoethane}$
• C. $\mathrm{Bromobutane}>\mathrm{Bromopropane}>\mathrm{Bromoethane}>\mathrm{Bromomethane}$
• D. $\mathrm{Bromoethane}>\mathrm{Bromomethane}>\mathrm{Bromobutane}>\mathrm{Bromopropane}$

Answer 1

The correct option is C

$\mathrm{Bromobutane}>\mathrm{Bromopropane}>\mathrm{Bromoethane}>\mathrm{Bromomethane}$

Explanation for correct option:

(C) $\mathrm{Bromobutane}>\mathrm{Bromopropane}>\mathrm{Bromoethane}>\mathrm{Bromomethane}$

• The boiling point of haloalkanes decreases with an increase in the number of hydrocarbons in the chain.
• Haloalkanes are nothing but hydrocarbon with electronegative halogen atoms.
• The decreasing order of haloalkanes: The Bromo methane is having the least boiling point ${\mathrm{CH}}_3\mathrm{Br}$, and then there is an ${\mathrm{CH}}_2$increase in Bromo ethane and ${\mathrm{CH}}_2$ increase in Bromo propane and an ${\mathrm{CH}}_2$ increase in Bromo butane which is having higher boiling point than others.
• So, the boiling point of haloalkanes is in the order:
• $\mathrm{Bromobutane}>\mathrm{Bromopropane}>\mathrm{Bromoethane}>\mathrm{Bromomethane}$

Hence, this is the correct option.

Explanation for incorrect option:

(A) $\mathrm{Bromomethane}>\mathrm{Bromoethane}>\mathrm{Bromopropane}>\mathrm{Bromobutane}$

• The Bromo methane should have a lower boiling point. So, this is an incorrect option.

(B) $\mathrm{Bromobutane}>\mathrm{Bromopropane}>\mathrm{Bromomethane}>\mathrm{Bromoethane}$

• The above order does not follow the trend of increasing hydrocarbon chan. So, this is an incorrect option.

(D) $\mathrm{Bromoethane}>\mathrm{Bromomethane}>\mathrm{Bromobutane}>\mathrm{Bromopropane}$

• The above order does not follow the trend of increasing hydrocarbon chan. So, this is an incorrect option.

Hence, the correct option is (C) $\mathrm{Bromobutane}>\mathrm{Bromopropane}>\mathrm{Bromoethane}>\mathrm{Bromomethane}$