Question

What is the hybridization of each carbon atom in acetonitrile (Problem \(1.25\) )?

Short answer

The first carbon is \(sp^3\) hybridized, and the second carbon is \(sp\) hybridized.

Step-by-step solution

Understand the Molecular Structure

Acetonitrile has the molecular formula \\(\text{CH}_3\text{CN}\). It consists of a methyl group (\(\text{CH}_3\)) and a cyano group (\(\text{CN}\)) connected together. This molecule has two carbon atoms: the first in the methyl group and the second in the cyano group.

Determine the Hybridization of the First Carbon Atom

The first carbon atom is part of the methyl group (\(\text{CH}_3\)). Carbon forms four sigma bonds (three with hydrogen atoms and one with the second carbon atom). To form these four sigma bonds, the carbon atom undergoes \(sp^3\) hybridization.

Determine the Hybridization of the Second Carbon Atom

The second carbon atom is part of the cyano group (\(\text{CN}\)). It is triple-bonded to the nitrogen atom and single-bonded to the first carbon, resulting in one sigma bond and two pi bonds. To accommodate a triple bond, the carbon uses \(sp\) hybridization, using one \(s\) orbital and one \(p\) orbital.

Key concepts

Acetonitrile

Acetonitrile, sometimes referred to as methyl cyanide, is an organic molecule with the chemical formula \( ext{CH}_3 ext{CN}\). This molecule is composed of two main parts: a methyl group \(( ext{CH}_3)\) and a cyano group \(( ext{CN})\). Acetonitrile is colorless and has a faint, sweet odor. It is important in the chemical industry, serving as a solvent used in the purification of butadiene during the manufacture of synthetic rubber. Acetonitrile is also utilized in the pharmaceutical industry and in electrochemistry applications. Understanding its structure is important for predicting its chemical behavior.

Molecular Structure

The molecular structure of a compound provides vital information about the arrangement of its atoms and the types of bonds they form. In the case of acetonitrile, the \( ext{CH}_3\) and \( ext{CN}\) groups are connected via a carbon-carbon single bond.

• The \( ext{CH}_3\) group is characterized by three hydrogen atoms bonded to a carbon atom.
• The \( ext{CN}\) group features a triple bond between carbon and nitrogen.

The understanding of molecular structure helps in determining the changes that occur during chemical reactions and can predict the physical properties of the substance.

Sigma Bonds

Sigma bonds, represented by the Greek letter \(\sigma\), signify the strongest type of covalent chemical bond. These bonds are formed by the head-on overlapping of atomic orbitals. In acetonitrile, the first carbon atom forms four sigma bonds.

• Three sigma bonds are created between the carbon atom and the hydrogen atoms in the \( ext{CH}_3\) group.
• The fourth sigma bond is with the carbon atom in the \( ext{CN}\) group.

These bonds result from the \(sp^3\) hybridization of the carbon atom in the methyl group. Additionally, the carbon in the \( ext{CN}\) group forms a sigma bond with nitrogen, post \(sp\) hybridization.

Pi Bonds

Pi bonds (\(\pi\)) are a type of covalent bond that is weaker than sigma bonds. They are formed by the side-to-side overlap of \(p\) orbitals. In acetonitrile, pi bonds are associated with the \(\text{CN}\) group's carbon-nitrogen triple bond.

• The second carbon atom shares its remaining \(p\) orbitals with nitrogen to form two pi bonds.
• The triple bond in \(\text{CN}\) consists of one sigma bond and two pi bonds, enabling the molecule's linear arrangement.

Pi bonds are crucial for defining the shape and stability of unsaturated substances such as acetonitrile. Understanding these bonds is essential for studying complex organic reactions.