Question

Consider the following haloalkanes:

$1.C{H}_{3}F2.C{H}_{3}Cl3.C{H}_{3}Br4.C{H}_{3}I$

The increasing order of reactivity in nucleophilic substitution reaction is:

• A. $1<2<4<3$
• B. $1<2<3<4$
• C. $1<3<2<4$
• D. $4<3<2<1$

Answer 1

Answer: (B)

$1<2<3<4$

The bond strength falls as you go from $C-F$ to $C-I$, and notice how much stronger the carbon-fluorine bond is than the rest. To react with the alkyl halides, the carbon-halogen bond has got to be broken. Because that gets easier as you go from fluoride to chloride to bromide to iodide, the compounds get more reactive in that order. Iodoalkanes are the most reactive and fluoroalkanes are the least.