Hyperconjugation is the stabilising interaction that results from the interaction of the electrons in a σ -bond (usually C−H ) with an adjacent empty or partially filled p -orbital or a π -orbital to give an extended molecular orbitalthatincreases the stability of the system. Consider the molecule propene, where π bond is in conjugation with 3σC−H bond of adjacent methyl group. So, higher the number of adjacent σC−H bond to π-bond higher will be the hyperconjugation and higher will be the stability. 2.
(IV) The adjacent σC−H bond to π bond increases in the order of IV > III > II > I. Therefore, stability follows the same order.