What is the order of reactivity of these alkenes
`(CH_(3))_(2)C=CH_(2)(I), CH_(3)CH=CH_(2)(II) and `CH_(2)=CH_(2)(III)` when subject to acid - catalysed hydration?

Options

A. `III gt II gt I`
B. `I gt III gt II`
C. `I gt II gt III`
D. `II gt I gt III`

Answer

C

Explanation

Acid catalysed hydration of alkenes proceeds through formation of carbocation.
` underset(I)(CH_(3))_(2)C= CH_(2) overset(H^(+)) (CH_(3))_(2)C^(+)- CH_(3)`
`underset(II)CH_(3) CH= CH_(2) overset(H^(+))to CH_(3)C^(+)H-CH_(3)`
`underset(III)CH_(2)= CH_(2) overset("H^(+)) to C^(+)H_(2)-CH_(3)`
Alkene which gives more stable carbocation will be more reactive. Here alkene I gives tertiary carbocation, II gives `2^(@)` carbocation and III gives `1^(@)` carbocation. Order of stability of carbocations is `3^(@) > 2^(@) > 1^(@)`. Therefore, order of reactivity of alkenes is `I gt II gt III`.