Question

$C{H}_3\underset{C{H}_3}{\underset{|}{C}H}-CH=C{H}_2\stackrel{\text{HBr, Peroxide}}{\to }C{H}_3\underset{C{H}_3}{\underset{|}{C}H}C{H}_{2}C{H}_{2}Br$

Which of the species below is an intermediate in the reaction?

• A. $C{H}_3\underset{C{H}_3}{\underset{|}{C}H}\stackrel{\bullet }{C}HC{H}_3$
• B. $C{H}_3\underset{C{H}_3}{\underset{|}{C}H}\stackrel{\bullet }{C}HC{H}_{2}Br$
• C. $C{H}_3\underset{C{H}_3}{\underset{|}{C}H}C{H}_2\stackrel{\oplus }{C}{H}_2$
• D. $C{H}_3\underset{C{H}_3}{\underset{|}{C}H}\stackrel{\oplus }{C}HC{H}_{2}Br$

Answer 1

The correct option is B $C{H}_3\underset{C{H}_3}{\underset{|}{C}H}\stackrel{\bullet }{C}HC{H}_{2}Br$

$C{H}_3-\underset{C{H}_3}{\underset{|}{C}H}-CH=C{H}_2+B{r}^{\bullet }⟶C{H}_3-\underset{C{H}_3}{\underset{|}{C}H}-\stackrel{\bullet }{C}H-C{H}_{2}Br$

Anti-Markovnikov addition:

In an addition reaction of an electrophile HX to an alkene or alkyne, the hydrogen atom of HX becomes bonded to the carbon atom that had the least number of hydrogen atoms in the starting alkene or alkyne. it occurs through a free radical mechanism.

Most stable radical is tertiary radical but gives secondary radical due to anti-markovnikov addition giving the above compound.