Arrange the following alkyl bromides in order of decreasing reactivity in an SN2 reaction:
l-bromo-2-methylbutane, l-bromo-3-methylbutane, 2-bromo-2-methylbutane, and 1-bromopcntane.
Step 1 of 3</p>
The mechanism of an reaction involves a backside attack by the nucleophile on the substrate and is thus accompanied by a crowding at the reaction site in transition state.
More crowding would mean more hindrance and less reactivity. Thus, among all the least reactivity towards reaction is shown by 2-bromo-2-methylbutane.
Step 2 of 3</p>
In reaction, the nucleophile attacks from the back of the leaving group. So, the more the branching at carbon or the carbons adjacent to it, less will be the probability of back side attack resulting in decrease in products. Thus, 1-bromo-2-methylbutane is the least reactive among the other three compounds.