Arrange the following alkenes A`to ` D, towards order of increasing reactivity in cationic polymerisation:
` Aimplies H_2 C = CHCH_3," " B impliesCICH=CH_2`
` Cimplies H_2 C =CH C_6H_5`
` Dimplies H_2 C =CHCOOCH_3`

Explanation

Reactivity of an alkene towards cationic polymerisation increases as the stability of the intermediate carbocation formed increases. The increasing order of the stability of the carbocation is as follows:
`H_3 C- overset(+ )(CH) COOCH_3 lt H_3 C- overset(+)(CH)-Cl lt CH_3 - overet(+)(CH) - CH_3 lt CH_3 - overset(+)(CH)-C_6 H_5 `
Therefore, the reactivity of the corresponding alkene towards cationic polymerisation increases in the same order as
`H_2 C=CHCOOCH_3 lt CH_2= CHCl lt CH_2 = CHCH_3 lt CH_2 =CHC_6 H_5 or D lt B lt A lt C`