Question

Which one of the following is the incorrect order of boiling points of the alkyl/aryl halides?

• A. ${\mathrm{CHCl}}_3>{\mathrm{CH}}_2{\mathrm{Cl}}_2$
• B. ${\mathrm{CH}}_3{\left({\mathrm{CH}}_2\right)}_3\mathrm{Cl}>{\mathrm{CH}}_3{\left({\mathrm{CH}}_2\right)}_2\mathrm{Cl}$
• C. ${\left({\mathrm{CH}}_3\right)}_3\mathrm{CCl}>{\left({\mathrm{CH}}_3\right)}_2{\mathrm{CHCH}}_2\mathrm{Cl}$
• D. ${\mathrm{CH}}_3{\left({\mathrm{CH}}_2\right)}_3\mathrm{Cl}>{\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CHCICH}}_3$

Answer 1

The correct option is C

${\left({\mathrm{CH}}_3\right)}_3\mathrm{CCl}>{\left({\mathrm{CH}}_3\right)}_2{\mathrm{CHCH}}_2\mathrm{Cl}$

Explanation for the correct option:

(c ) ${\left({\mathrm{CH}}_3\right)}_3\mathrm{CCl}>{\left({\mathrm{CH}}_3\right)}_2{\mathrm{CHCH}}_2\mathrm{Cl}$

• For isomeric alkyl halide, the boiling point decrease with branching.
• This is because, with branching, the surface area of alkyl halide decreases, and hence, the magnitude of Vanderwall forces of attraction decreases.
• The boiling point of ${\left({\mathrm{CH}}_3\right)}_3\mathrm{CCl}$is lower than that of ${\left({\mathrm{CH}}_3\right)}_2{\mathrm{CHCH}}_2\mathrm{Cl}$.
• Hence this option is correct.

Explanation for the incorrect options:

(a) ${\mathrm{CHCl}}_3>{\mathrm{CH}}_2{\mathrm{Cl}}_2$

• The molecular mass of ${\mathrm{CHCl}}_3$is greater than ${\mathrm{CH}}_2{\mathrm{Cl}}_2$.
• So, the boiling point of ${\mathrm{CH}}_2{\mathrm{Cl}}_2$is lower than that of ${\mathrm{CHCl}}_3$.
• Hence this option is not correct

(b)${\mathrm{CH}}_3{\left({\mathrm{CH}}_2\right)}_3\mathrm{Cl}>{\mathrm{CH}}_3{\left({\mathrm{CH}}_2\right)}_2\mathrm{Cl}$

• For the same halogen atom, the boiling point increase with the increase in the size of the alkyl group.
• So, the boiling point of ${\mathrm{CH}}_3{\left({\mathrm{CH}}_2\right)}_3\mathrm{Cl}$is greater than ${\mathrm{CH}}_3{\left({\mathrm{CH}}_2\right)}_2\mathrm{Cl}$.
• Hence this option is not correct.

(d) ${\mathrm{CH}}_3{\left({\mathrm{CH}}_2\right)}_3\mathrm{Cl}>{\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CHCICH}}_3$

• For isomeric alkyl halide, the boiling point decrease with branching.
• This is because, with branching, the surface area of alkyl halide decreases, and hence, the magnitude of vanderwall forces of attraction decreases.
• So, the boiling point of ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CHCICH}}_3$is lower than that of ${\mathrm{CH}}_3{\left({\mathrm{CH}}_2\right)}_3\mathrm{Cl}$.
• Hence this option is not correct

Hence the correct option is (c ) ${\left({\mathrm{CH}}_3\right)}_3\mathrm{CCl}>{\left({\mathrm{CH}}_3\right)}_2{\mathrm{CHCH}}_2\mathrm{Cl}$