The rate of beta-dehydrohalogenation in the f | vedclass

Name: Exam Paper Generator | JEE NEET Paper Generator | Vedclass
Brand: Vedclass
Rating: 5 (35 reviews)

Question

(A) The $\beta$-dehydrohalogenation reaction proceeds via an $E2$ mechanism,which involves the abstraction of a $\beta$-hydrogen by a strong base.In t

Vedclass · Accepted Answer

$a > b > c$

Vedclass · Answer

(A) The $\beta$-dehydrohalogenation reaction proceeds via an $E2$ mechanism,which involves the abstraction of a $\beta$-hydrogen by a strong base.In this reaction,the rate-determining step involves the breaking of the $C-H$ or $C-D$ bond at the $\beta$-position.Since the $C-D$ bond is stronger than the $C-H$ bond due to the primary kinetic isotope effect,the cleavage of the $C-H$ bond is faster than that of the $C-D$ bond.Compound $(a)$ has two $\beta$-hydrogens $(Ph-CH_2-CH_2-Br)$,making it the fastest.Compound $(b)$ has two $\beta$-deuteriums $(Ph-CD_2-CH_2-Br)$,making it slower than $(a)$ due to the isotope effect.Compound $(c)$ $(CD_3-CH_2-Br)$ also has $\beta$-deuteriums,but the electron-donating effect of the phenyl ring in $(b)$ stabilizes the transition state more effectively than the methyl group in $(c)$,making $(b)$ faster than $(c)$.Thus,the order of the rate of reaction is $a > b > c$.

The rate of $\beta$-dehydrohalogenation in the following halides under treatment with a strong base follows the order:

Similar Questions

$(i) \, (CH_3)_2CH-CH_2Br \xrightarrow{C_2H_5OH} (CH_3)_2CH-CH_2OC_2H_5 + HBr$
$(ii) \, (CH_3)_2CH-CH_2Br \xrightarrow{C_2H_5O^-} (CH_3)_2CH-CH_2OC_2H_5 + Br^-$
The reaction mechanisms for $(i)$ and $(ii)$ are respectively:

The decreasing order of reactivity towards $S_N 1$ reaction for the following compounds is:

What is the major product of the following reaction?
$CH_2=CH-CH_2-CH(Br)-CH_3 + KOH \xrightarrow[\text{heat}]{\text{alcohol}} \dots$

What is the major product formed when $2$-bromopentane is heated with ethanolic potassium ethoxide $(C_2H_5OK)$?

Which of the following are correct statements about $C_2H_5Br$?

Vedclass Test Series

Exam Paper Generator

Online Exam Module