The inductive effect of the alkyl group on a saturated carbon chain follows the order (CH3)3C−>(CH3)2CH−>CH3−CH2−>CH3 However, when an alkyl group is attached to an unsaturated system such as double bond or a benzene ring, the order of inductive effect is actually reversed. This effect is called hyper conjugation effect or Baker-Nathan effect. Now, the reactivity order is (CH3)3C−<(CH3)2CH−<CH3−CH2−<CH3−