Haloalkanes and Haloarenes - Result Question 21
####21. Reactivityorder of halides for dehydrohalogenation is
[2002]
(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) $R-F>R-I>R-Br>R-Cl$
Show Answer
Solution:
- (b) The order of atomic size of halogens decrease in the order $I>Br>Cl>F$
i.e on moving down a group atomic size increases. Further the bond length of $C-X$ bond decreases in the order
$C-I>C-Br>C-Cl>C-F$
and hence the bond dissociation energy decreases in the order
$R-F>R-Cl>R-Br>R-I$
hence $R-I$ being a weakest bond break most easily. Hence R - I is most reactive.
