Question

Consider the following carbocations
i:$C_6{H}_5\stackrel{+}{C}{H}_2$
ii:$C_6{H}_{5}C{H}_2\stackrel{+}{C}{H}_2$
iii:$C_6{H}_5\stackrel{+}{C}{H}_{2}C{H}_3$
iv:$C_6{H}_5\stackrel{+}{C}(C{H}_3{)}_2$
The correct sequence for the stability of these is:

• A. ii < i < iii < iv
• B. ii < iii < i < iv
• C. iii < i < ii
• D. iv < iii < i < ii

Answer 1

The correct option is A ii < i < iii < iv

Stability of carbocation: Benzene $>$ Allyl $>$ $3^o>2^o>1^o$

Benzyl and Allyl are stabilized by resonance.

1. $C_6{H}_5\stackrel{+}{C}{H}_2$ -$1^{o}Benzyl$

2. $C_6{H}_{5}C{H}_2\stackrel{+}{C}{H}_2-1^o$

3. $C_6{H}_5\stackrel{+}{C}{H}_{2}C{H}_3-2^{o}Benzyl$

4. $C_6{H}_5\stackrel{+}{C}(C{H}_3{)}_2-3^{o}Benzyl$

So order is $4>3>1>2$