Question

There are some alkenes are given as follow:

2-methyl propene, cis-2-butene, trans-2-butene

Which of the following is the correct order for increasing order of reactivity for acid catalyzed hydration?

1) trans-2-butene< cis-2-butene < 2-methyl propene

2) cis-2-butene< trans-2-butene < 2-methyl propene

3) 2-methyl propene < trans-2-butene < cis-2-butene

Answer 1

The correct order of increasing reactivity towards acid catalyzed hydration is
trans-2-butene< cis-2-butene< 2-methyl propene . As the number of alkyl groups attached to the carbon atoms increases, the +I effect of the alkyl groups increases and the alkene becomes electron rich. Hence, the reactivity towards acid catalyzed hydration increases as pi electrons of the double bond are donated to proton. Also as the stability of alkene decreases (cis isomer is less stable than trans isomer), the reactivity towards acid catalyzed hydration increases.