Question

What is the hybridization of each carbon atom in acetonitrile (Problem \(1-26\) )?

Short answer

The first carbon is sp³ hybridized, and the second is sp hybridized.

Step-by-step solution

Identifying Atoms

Acetonitrile, with the chemical formula CH₃CN, consists of two carbon atoms. We need to identify the hybridization of each of these carbon atoms.

Analyzing the CH₃ Group

The first carbon atom is in the methyl group (CH₃). This carbon forms three single bonds with hydrogen atoms and one sigma bond with the adjacent carbon in the CN group. The presence of four sigma bonds indicates that the carbon is sp³ hybridized.

Analyzing the CN Group

The second carbon is in the cyanide group (CN). This carbon forms a triple bond with the nitrogen atom. A carbon forming a triple bond is typically sp hybridized. This is because it participates in two pi bonds (accounting for four p orbitals) in a triple bond, with remaining (s) orbital contributing to sigma bond with adjacent carbon atom.

Key concepts

Acetonitrile

Acetonitrile is an organic compound and is the simplest organic nitrile. It appears as a colorless liquid possessing a sweet odor reminiscent of ether. Its chemical formula is CH₃CN, indicating it contains two carbon atoms, a methyl group (CH₃), and a cyanide group (CN).
Acetonitrile is widely used as a solvent in the pharmaceutical industry, particularly for drug extraction and purification. The carbon atoms in acetonitrile exhibit different hybridizations due to their differing bonding environments.
In acetonitrile, understanding the hybridization of each carbon atom is crucial, as it dictates the molecule's geometry and reactivity. The hybridization explains how atoms form bonds in specific spatial orientations, impacting the molecule's chemical behavior.

sp³ hybridization

In chemistry, sp³ hybridization refers to the mixing of one s orbital and three p orbitals from the same atom to create four equivalent hybrid orbitals. These orbitals form sigma bonds, leading to a tetrahedral geometry with 109.5° bond angles.
In acetonitrile, the first carbon atom is part of the methyl group (CH₃). It bonds with three hydrogen atoms and one carbon atom from the CN group. These four sigma bonds indicate that this carbon is sp³ hybridized. This setup gives a tetrahedral shape ensuring stable bonds with other atoms.

• Each bond in the CH₃ group uses one of the sp³ hybrid orbitals.
• The equal energy of sp³ orbitals allows for uniform bond lengths and strengths.

This hybridization explains why methyl groups are often more stable and less reactive, as the tetrahedral arrangement minimizes electron pair repulsion.

sp hybridization

The concept of sp hybridization involves mixing one s orbital with one p orbital, resulting in two linear hybrid orbitals. These orbitals create sigma bonds along a straight line with 180° bond angles, allowing for the formation of triple bonds.
In acetonitrile, the second carbon atom is in the cyanide group (CN), which forms a triple bond with a nitrogen atom. In such configurations, the carbon atom uses sp hybridization.
This happens because this carbon forms:

• One sigma bond with the nitrogen atom using the sp hybrid orbital.
• Two pi bonds with the nitrogen atom, formed by the unhybridized p orbitals.

The linear structure of sp hybridized atoms allows molecules like acetonitrile to be highly reactive, especially in forming and breaking multiple bonds with other atoms.