Question

In which option correct rate for step-2 is given for the different R-X

• A. $C{H}_3-C{H}_2-Br<C{H}_3-\underset{Br}{\underset{|}{CH}}-C{H}_3$
• B. $Ph-Cl>{CH}_3-Cl$
• C. $Ph-{CH}_2-Br>Ph-CH-{CH}_3$
• D. ${CH}_2=CH-{CH}_2-Cl>{CH}_3-{CH}_2$

Answer 1

The correct option is A $C{H}_3-C{H}_2-Br<C{H}_3-\underset{Br}{\underset{|}{CH}}-C{H}_3$

$C{H}_3-C{H}_2-Br<C{H}_3-\underset{Br}{\underset{|}{CH}}-C{H}_3$

In $2^{nd}$ - step a carbocation is formed as the intermediate and the rate of reaction depends upon the stability of carbocation. Since, $2^o$ carbocation is more stable than $1^o$ carbocation because of more hyperconjugable hydrogen atom in $2^o$ than in $1^o$ i.e., 6 in $2^o$ and $3$ in $1^o$

$\underset{2^o-Carbocation}{H_5-\underset{H_6}{\underset{|}{\stackrel{H_4}{\stackrel{|}{C}}}}-\underset{\oplus }{\stackrel{H}{\stackrel{|}{C}}}-\underset{H_3}{\underset{|}{\stackrel{H_1}{\stackrel{|}{C}}}}-H_2}$ $\underset{1^o-carbocation}{H_2-\underset{H_3}{\underset{|}{\stackrel{H_1}{\stackrel{|}{C}}}}-\underset{H}{\underset{|}{\stackrel{H}{\stackrel{|}{C}}}}\oplus }$