Question

Which of the following order is incorrect for the rate of $E_2$ reaction?

• A. $\text{5-Bromocycloheptene > 4-Bromocycloheptene}$
• B. $\text{2-Bromo-1 - phenylbutane > 3-Bromo- 1 -phenylbutane}$
• C. $\text{3-Bromocyclohexene > Bromocyclohexane}$
• D. $\text{3-Bromo- 2 -methylpentane > 2-Bromo-4-methylpentane}$

Answer 1

The correct option is C $\text{3-Bromocyclohexene > Bromocyclohexane}$

Product formed by $E2$ of 4-Bromocycloheptene is more stable than 5-Bromocycloheptene becuase it is a conjugated alkene. So, rate of reaction for 4-Bromocycloheptene is faster than 5-Bromocycloheptene.
Rate of reaction for 2-Bromo - 1 -phenylbutane is more than 3-Bromo - 1 - phenylbutane as product formed in former is more stable due to resonance.
Rate of reaction of E2 for 3-Bromocyclohexene is more than Bromocyclohexane as product formed in former is more stable since it is a conjugated diene.
Rate of reaction of E2 for 3-Bromo- 2 -methylpentane is more than 2-Bromo-4-methylpentane as product formed in former is more stable (more substituted).