Question

The shape of carbocation is :

• A. trigonal planar
• B. diagonal pyramidal
• C. tetrahedral
• D. diagonal

Answer 1

The Correct Option is A

To determine the shape of a carbocation, we need to understand the electronic configuration and hybridization involved when a carbocation forms.

A carbocation is a positively charged carbon atom with only six electrons in its valence shell. Because it is electron-deficient, it lacks an octet and thus cannot exhibit tetrahedral geometry, which requires an electron pair for each bond in a 3D space.

The most stable configuration that a carbocation can achieve is trigonal planar. Here is the reasoning behind this:

1. The central carbon atom in a carbocation is sp² hybridized. This means that it uses three sp² hybrid orbitals to form sigma bonds with surrounding atoms.
2. Since there are only three sigma bonds, the atoms connected to the carbocation form a plane around the central carbon atom.
3. The unhybridized p orbital on the carbocation carbon is perpendicular to this plane, which is a distinctive feature of trigonal planar geometry.

Therefore, the correct answer, based on hybridization and geometry theory, is that a carbocation takes a trigonal planar shape.

Let's briefly consider why the other options are incorrect:

• Diagonal pyramidal: This is not a recognized geometric term in molecular geometry.
• Tetrahedral: This shape requires the carbon to have four regions of electron density (like in methane, \(\text{CH}_4\)), which is not the case for electron-deficient carbocations.
• Diagonal: Similar to diagonal pyramidal, this is not a term used in molecular geometry for describing the shape of molecules.

Thus, considering all the points, the shape of the carbocation is trigonal planar.

Answer 2

A carbocation has a central carbon atom with three bonded groups and one empty {p}-orbital. The geometry around the carbocation is trigonal planar because the three groups are arranged at 120$^\circ$ to minimize electron repulsion.
\[\textbf{Carbocation structure:} \quad \text{H-C$^+$-H}.\]
The trigonal planar shape is due to {sp}$^2$-hybridization of the central carbon atom.