The most stable carbocation is:

Options

A. `CH_(3)^(+)`
B. `CH_(3)CH_(2)^(+)`
C. `(CH_(3))_(3)C^(+)`
D. `(CH_(3))_(2)CH^(+)`

Answer

C

Explanation

In comparison to `H` atoms, alkyl groups are electron releasing, i.e., they have `+I` effect. This implies that when an alkyl group is bonded to the positively charged `C` atom of a carbocation, it will shift electron density toward the positive charged `C` atom. Through electron release, alkyl groups attached to the positive `C` atom of a carbocation disperse (or delocalize) the positive charge.. In doing so, the attached alkyl groups acquire some amount of the positive charge and thus stabilize the carbocation.
In the tert-butyl cation `(CH_(3))_(3)C^(+)`, three electron releasing methyl groups surround the central `C` atom and assist in delocalizing the positive charge. In the isopropyl cation, `(CH_(3))_(2)CH^(+)`, there are only two attached methyl group that can serve to delocalize the charge. In the ethyl cation, there is only one attached methyl group, and in the methyl cation, there is none at all. As a result, the delocalization of charge and the order of stability of the carbocations parallel the number of attached methyl groups:
`(CH_(3))_(3)C^(+) gt (CH_(3))_(2)H^(+) gt CH_(3)CH_(2)^(+) gt CH_(3)^(+)`