Question

When subjected to acid catalysed hydration, the order of reactivity of the alkenes; $\left( CH _{3}\right)_{2} C = CH _{2}( I ), CH _{3} CH = CH _{2}(II)$ and $CH _{2}= CH _{2}(III)$ is

• A. III > II > I
• B. I > III > II
• C. I > II > III
• D. II > I > III

Answer 1

Answer: (C)

I > II > III

Answer 2

Acid catalysed hydration of alkenes involves formation of carbocation intermediate. Higher the stability of carbocation intermediate, more is the reactivity towards acid catalysed hydration. The order of stability of carbocations (formed) is
$\left( CH _{3}\right)_{2} \overset{+}{ C}CH _{3}> CH _{3} \overset{+}{ C } HCH _{3}>\overset{+}{ C } H _{2}- CH _{3}$
Thus, the order of reactivity towards acid catalysed hydration is
$\underset{(I)}{\left( CH _{3}\right)_{2} C} = CH _{2}> \underset{(II)}{CH _{3} CH} = CH _{2}> \underset{(III)}{CH _{2}= CH _{2}}$