Question

Reactivity order of halides for dehydrohalogenation is:
[1 mark]

• A. $R-F>R-Cl>R-Br>R-I$
• B. $R-I>R-Br>R-Cl>R-F$
• C. $R-I>R-Cl>R-Br>R-F$
• D. $R-F>R-I>R-Br>R-Cl$

Answer 1

The correct option is B $R-I>R-Br>R-Cl>R-F$

$F,Cl,Br$ and $I$ belong to the same group. Atomic radii go on increasing down a group. As the halogen becomes larger on going down the group, $R-X$ bond also becomes weaker. The decreasing order of bond length. is $C-I>C-Br>C-Cl>C-F$.
During dehydrohalogenation $C-I$ bond breaks more easily than $C-F$ bond. So reactivity order of halides is
$R-I>R-Br>R-Cl>R-F$.