Question

The decreasing order of boiling points of alkyl halides is

• A. $RI>RBr>RCl>RF$
• B. $RF>RCI>RBr>Rl$
• C. $RBr>RCl>RI>RF$
• D. $RCl>RF>Rl>RBr$

Answer 1

The correct option is A $RI>RBr>RCl>RF$

The boiling points of alkyl and aryl halides increase with increase in the molecular size or molecular weight. Although the dipole-dipole interaction is same for all the alkyl halide carry same halogen moiety, the contributing effect is produced by van der waal force of attraction which depends on the size of the molecule. As the size increases, Van der waal force of attraction also increase. It requires more amount of energy to break the attractive force in between the particle in solid and liquid state hence boiling point increases with increase in molecular size or weight.

In case of alkyl halide with same alkyl group and different halogen, boiling point increases from alkyl fluorides to alkyl iodide. This is due to increase in the size of molecule with increase in the size of halogen atom. thus correct boiling point order is $RI>RBr>RCl>RF.$