In a S_(N)2 substitution reaction of the type R-Br+Cl^(-) overset(DMF)to R-Cl+Br^(-), which of the following has the highest reactivity rate?

In a S_(N)2 substitution reaction of the type R-Br+Cl^(-) overset(DMF)

1.	In a S_(N)2 substitution reaction of the type R-Br+Cl^(-) overset(DMF)to R-Cl+Br^(-), which of the following has the highest reactivity rate?
Answer» `CH_(3)-underset(CH_(3))underset(\|)CH-CH_(2)Br` `CH_(3)-underset(CH_(3))underset(\|)overset(CH_(3))overset(\|)C-CH_(2)Br` `CH_(3)CH_(2)Br` `CH_(3)-CH_(2)-CH_(2)Br` Solution :Rate of `S_(N)2` reaction DECREASES with INCREASE in steric hindrance. SINCE `CH_(3)CH_(4)Br` has the least STEARIC hindrance, it reacts at the fastest rate.