Question

What are hybridisation states of each carbon atom in the following compounds? \(\mathrm{CH}_{2}=\mathrm{C}=\mathrm{O}, \mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2},\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO}, \mathrm{CH}_{2}=\mathrm{CHCN}, \mathrm{C}_{6} \mathrm{H}_{6}\)

Short answer

\(\mathrm{CH}_{2}=\mathrm{C}=\mathrm{O}:\) sp; \(\mathrm{CH}_{3}\mathrm{CH}=\mathrm{CH}_{2}:\) sp³, sp², sp²; \((\mathrm{CH}_3)_2\mathrm{CO}:\) sp³, sp²; \(\mathrm{CH}_{2}=\mathrm{CHCN}:\) sp², sp; \(\mathrm{C}_6\mathrm{H}_6:\) all sp².

Step-by-step solution

Identify Each Carbon Compound

We have five compounds: \(\mathrm{CH}_{2}=\mathrm{C}=\mathrm{O}\), \(\mathrm{CH}_{3}\mathrm{CH}=\mathrm{CH}_{2}\), \((\mathrm{CH}_{3})_{2} \mathrm{CO}\), \(\mathrm{CH}_{2}=\mathrm{CHCN}\), and \(\mathrm{C}_{6} \mathrm{H}_{6}\). We need to determine the hybridization state of each carbon atom within these compounds.

Analyze Compound 1: \(\mathrm{CH}_{2}=\mathrm{C}=\mathrm{O}\)

The compound has two double-bonded oxygen and hydrogen atoms. The central carbon atom is attached to two atoms through double bonds. This indicates sp hybridization for the central carbon because it forms two \(\sigma\) bonds and two \(\pi\) bonds.

Analyze Compound 2: \(\mathrm{CH}_{3}\mathrm{CH}=\mathrm{CH}_{2}\)

In this compound, the first carbon is bonded to three hydrogens and one carbon, hence sp³. The second carbon forms a double bond with the third carbon and a single bond with another carbon, so it is sp² hybridized. The third carbon, having a double bond with the second carbon and single hydrogen bonds, is also sp² hybridized.

Analyze Compound 3: \((\mathrm{CH}_{3})_{2} \mathrm{CO}\)

Both methyl carbons (connected to three hydrogens and one carbon) are sp³ hybridized. The central carbon (to which both set of methyl groups and the oxygen are bonded) forms a double bond with oxygen, giving it sp² hybridization.

Analyze Compound 4: \(\mathrm{CH}_{2}=\mathrm{CHCN}\)

The first carbon in \(\mathrm{CH}_{2}\) is bonded to one carbon and two hydrogens, leading to sp² hybridization. The carbon in \(\mathrm{CH}\) forms a double bond with one carbon and a triple bond with nitrogen in \(\mathrm{CN}\), resulting in sp hybridization.

Analyze Compound 5: \(\mathrm{C}_{6} \mathrm{H}_{6}\)

This is benzene, where each carbon atom in the ring is bonded to one hydrogen and two other carbons in an alternating single and double-bond sequence. Thus all six carbon atoms are sp² hybridized.

Key concepts

Hybridization States

Hybridization states refer to the way atomic orbitals mix to form new hybrid orbitals suitable for the pairing with other atoms. These states indicate the geometry and bonding types in molecules. Each carbon atom can be in one of a few different hybridization states, mainly

• sp hybridization
• sp² hybridization
• sp³ hybridization

Carbon's hybridization state depends on the number and types of bonds it forms. Recognizing these states helps in predicting the shape and reactivity of organic molecules. By understanding carbon's hybridization, scientists can predict how a molecule interacts with others and what its physical properties might be.

sp Hybridization

In sp hybridization, one s orbital mixes with one p orbital to form two equal hybrid orbitals. This results in carbon atoms forming a linear shape, with a bond angle of 180 degrees. This type of hybridization occurs when a carbon atom:

• Forms two \(\sigma\) (single) bonds
• Forms two \(\pi\) (double) bonds, such as in an alkyne

An example is the carbon in the compound \[\mathrm{CH}_{2}=\mathrm{C}=\mathrm{O}\] here the central carbon forms a double bond with oxygen and one with the other carbon, enabling it to participate in sp hybridization.

sp² Hybridization

sp² hybridization involves one s orbital mixing with two p orbitals, creating three hybrid orbitals. These orbitals arrange themselves in a trigonal planar shape with bond angles of 120 degrees. A carbon atom in sp² hybridization forms:

• Three \(\sigma\) bonds
• One \(\pi\) bond, usually indicating a double bond

We see this in compounds like \[\mathrm{CH}_{3}\mathrm{CH}=\mathrm{CH}_{2}\] where the carbon atoms involved in double bonding are sp² hybridized. This allows for a flat molecular structure which is common in alkenes and in the aromatic ring of benzene,\[\mathrm{C}_{6}\mathrm{H}_{6}\].

sp³ Hybridization

In sp³ hybridization, one s orbital blends with three p orbitals, forming four identical hybrid orbitals. This arrangement results in a tetrahedral geometry with bond angles close to 109.5 degrees. Carbon atoms in sp³ hybridization make:

• Four \(\sigma\) bonds, which are single bonds

An example of this hybridization is the compound \[\mathrm{CH}_{3}\mathrm{CH}_2\mathrm{CH}_3\] where all carbons predominantly make single bonds with hydrogen or other carbons. Such a configuration appears in saturated hydrocarbons, like alkanes, where no double or triple bonds are present.

Organic Chemistry

Organic chemistry is the branch of chemistry dealing with carbon-based compounds, particularly those involving the structuring and changes of organic molecules. Carbon's ability to engage in various hybridization states makes it incredibly versatile, leading to a multitude of organic compounds. With understanding hybridization:

• We can visualize the molecules' three-dimensional shapes
• Predict the molecular behavior
• Understand chemical reactions and mechanisms

The compounds in organic chemistry, such as benzene \[\mathrm{C}_{6}\mathrm{H}_{6}\], provide foundational knowledge for various applications, including pharmaceuticals, materials science, and biochemistry. It sets the stage for learning about complex reactions and synthesis methods essential in creating new materials and drugs.