Question

Correct order of boiling points among following is: $\underset{\left(X\right)}{C{H}_3(C{H}_2{)}_{3}C{H}_3},\underset{\left(Y\right)}{C_2{H}_{5}O{C}_2{H}_5},\underset{\left(Z\right)}{C{H}_3(C{H}_2{)}_{3}OH}$

• A. X > Y > Z
• B. Y > X > Z
• C. Z > X > Y
• D. Z > Y > X

Answer 1

The correct option is D Z > Y > X

The boiling point of a molecule depends on the strength of intermolecular interaction such as Vandewaal's attraction, hydrogen bonding etc.

Alkanes, such as $\underset{X}{C{H}_3(C{H}_2{)}_{3}C{H}_3}$, being non-polar have the weakest force of attraction called dispersion or London forces.

Ethers, such as $\underset{\left(Y\right)}{C_2{H}_{5}O{C}_2{H}_5}$, have small dipole moment or weakly polar thus have dipole-dipole interaction. This is stronger than the London forces.

Alcohols, such as $\underset{\left(Z\right)}{C{H}_3(C{H}_2{)}_{3}OH}$, are polar molecules, therefore, have strong dipolar interaction. Moreover, they form an intermolecular hydrogen bond that further increases the attraction (association).

Hence the order of their boiling point will be:

$\underset{\left(Z\right)}{C{H}_3(C{H}_2{)}_{3}OH}>\underset{\left(Y\right)}{C_2{H}_{5}O{C}_2{H}_5}>\underset{X}{C{H}_3(C{H}_2{)}_{3}C{H}_3}$

OR $Z>Y>X$