Arrange the compounds of each set in order of reactivity towards SN2 displacement.
1-Bromobutane, 1-Bromo-2, 2-dimethylpropane, 1-Bromo-2-methylbutane, 1-Bromo-3-methylbutane.
1-Bromobutane >1-Bromo-2-methylbutane > 1-Bromo-2, 2-dimethyl propane > 1-Bromo-3-methyl-butane.