Question

What will be the decreasing order of stability of following carbocations ?

• A. $3>5>4>1>2$
• B. $1>2>3>5>4$
• C. $5>4>3>2>1$
• D. $1>2>3>4>5$

Answer 1

Answer: (D)

Structure (I) is aromatic.

Structure (II) shows $-1$ effect due to presence of $N{\left(C{H}_3\right)}_3$ group, which destabilises the carbocation.

Structure (III) shows $-1$ and R-effects, which destabilises the carbocation more.

Structure (IV) contains positive charge on its ring. Hence, it is less stable than structures I, II and III.

Structure (V) contains positive charge with triple bond, which has high tendency to gain electrons. Hence, it is least stable among all.

$\therefore$ Decreasing order of stability

$I>II>III>IV>V$