Hydrocarbons Question 47
Question: Reaction of HBr with propene in the presence of peroxide gives [CBSE PMT 2004]
Options:
A) Allyl bromide
B) n-propyl bromide
C) Isopropyl bromide
D) 3-bromo propane
Show Answer
Answer:
Correct Answer: B
Solution:
The formation of n-propyl bromide in presence of peroxide can be explained as follows.
Step-1: Peroxide undergo fission to give free radicals $ R-O-O-R\to 2-R-\dot{O} $
Step-2 : $ HBr $ combines with free radical to form bromine free radical $ R-\dot{O}+HBr\to R-OH+B\dot{r} $
Step-3 : $ B\dot{r} $ attacks the double bond of the alkene to form a more stable free radical $ CH_3CH=CH_2+B\dot{r}<\begin{matrix} \underset{\text{(more stable)}}{\mathop{CH_3-\dot{C}H-CH_2Br}} \\ {} \\ \underset{\text{(less stable)}}{\mathop{CH_3-\overset{Br}{\mathop{\overset{|}{\mathop{C}}H}}-\dot{C}H_2}} \\ \end{matrix} $
Step-4 : More stable free radical attacks the $ HBr $
$ CH_3-\dot{C}H-CH_2-Br+HBr\to \underset{\text{n-propyl bromide}}{\mathop{CH_3CH_2CH_2Br}}+B\dot{r} $ Step-5 : $ B\dot{r}+B\dot{r}\to Br_2 $
BETA
