Question

Which of the following carbocation is most stable?
(A) ${{\left( C{{H}_{3}} \right)}_{3}}C{{C}^{+}}{{H}_{2}}$
(B) ${{\left( C{{H}_{3}} \right)}_{3}}{{C}^{+}}$
(C) $C{{H}_{3}}C{{H}_{2}}{{C}^{+}}{{H}_{2}}$
(D) $C{{H}_{3}}{{C}^{+}}HC{{H}_{2}}C{{H}_{3}}$

Answer 1

Hint The stability of carbocations depends upon some geometrical factors and resonance considerations. Knowing the general trend for the stability of carbocations
will help us answer the given illustration.

Complete step by step solution:
Let us see the basic of carbocations and the trend for its stability;
Carbocation- It is a molecule in which a carbon atom has a positive charge and the three bonds. Basically, it is a carbon cation.
Stability of carbocations- As, they have positive charge i.e. they are electron deficient. Thus, they will be the species which is always hungry for electrons. The stability of carbocations depends upon;
1. The number of adjacent carbon atoms i.e. increasing the number of carbon atoms will stabilize the carbocation.
2. Presence of adjacent pi-bonds which eventually allows the carbocation p-orbital to be a part of a conjugated pi-system.
3. Presence of adjacent atoms with lone pairs of electrons.
By this, we can say that the tertiary carbocation is more stable than that of primary and secondary carbocations. The general trend can be given for the following;
as, Methyl C. < Primary C. < Secondary C. < Tertiary C.
Thus, for the given illustration;
(A) ${{\left( C{{H}_{3}} \right)}_{3}}C{{C}^{+}}{{H}_{2}}$ - Primary carbocation
(B) ${{\left( C{{H}_{3}} \right)}_{3}}{{C}^{+}}$ - Tertiary carbocation
(C) $C{{H}_{3}}C{{H}_{2}}{{C}^{+}}{{H}_{2}}$ - Primary carbocation
(D) $C{{H}_{3}}{{C}^{+}}HC{{H}_{2}}C{{H}_{3}}$ - Secondary carbocation

Therefore, we can see that option (B) is correct.

Note: For the aromatic carbocations, presence of resonance effect is more vital than the hyperconjugation and inductive effect to stabilize the same. For them too, the trend for the stable carbocations will be same i.e.
Methyl C. < Primary C. < Secondary C. < Tertiary C.