Problem 132 - A Complete Resource Book in Chemistry for JEE Main

Question

Among the following compounds which has more than one type of hybridization for carbon atom? I. \(\mathrm{CH}_{3} \cdot \mathrm{CH}_{2} \cdot \mathrm{CH}_{2} \cdot \mathrm{CH}_{3}\) II. \(\mathrm{CH}_{3} \cdot \mathrm{CH}^{2}=\mathrm{CH}^{2} \cdot \mathrm{CH}_{3}\) III. \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C} \equiv \mathrm{CH}\) IV. \(\mathrm{CH}_{2}=\mathrm{CH}_{2}\) (a) II only (b) II and III (c) I and III (d) III and IV

Step-by-Step Solution

Answer

(b) II and III

Step 1: Analyze Compound I

Compound I is \( \mathrm{CH}_{3} \cdot \mathrm{CH}_{2} \cdot \mathrm{CH}_{2} \cdot \mathrm{CH}_{3} \). All carbon atoms in this compound are single-bonded, meaning all carbon atoms are \( sp^3 \) hybridized.

Step 2: Analyze Compound II

Compound II is \( \mathrm{CH}_{3} \cdot \mathrm{CH}^{2}=\mathrm{CH}^{2} \cdot \mathrm{CH}_{3} \). The two middle carbon atoms are involved in a double bond, i.e., they are \( sp^2 \) hybridized, while the terminal methyl groups \( \mathrm{CH}_3 \) are \( sp^3 \) hybridized. This compound features more than one type of hybridization.

Step 3: Analyze Compound III

Compound III is \( \mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C} \equiv \mathrm{CH} \). The first carbon is part of a double bond (\( sp^2 \) hybridized), the second is \( sp^2 \) hybridized, and the third one is \( sp \) hybridized due to the triple bond. This compound also has more than one type of hybridization.

Step 4: Analyze Compound IV

Compound IV is \( \mathrm{CH}_{2}=\mathrm{CH}_{2} \). All carbon atoms in this compound are part of double bonds, which results in all carbon atoms being \( sp^2 \) hybridized.

Step 5: Determine the Correct Answer

From the analysis, compounds II and III have more than one type of hybridization for carbon atoms. Compound II has \( sp^3 \) and \( sp^2 \) hybridization, while Compound III has \( sp \), \( sp^2 \), and \( sp \) hybridization, fitting the criteria of having different hybridizations.

Key Concepts

sp3 hybridization

When we talk about sp3 hybridization, we are referring to the type of hybridization that involves the mixing of one s orbital with three p orbitals. This type of hybridization forms four equivalent sp3 hybrid orbitals. Each of these orbitals has 25% s character and 75% p character.
These orbitals arrange themselves in a tetrahedral geometry to minimize repulsion, with bond angles of approximately 109.5 degrees.
Carbon atoms in molecules with only single bonds are typically sp3 hybridized. In compound I, for instance, the carbon atoms connect through single bonds. This makes all of them sp3 hybridized because there are no double or triple bonds: just sigma bonds, which are a result of sp3 hybrid orbitals overlapping.

• Example: Methane (CH4) is the classic illustration of sp3 hybridization, where the carbon forms four sigma bonds with hydrogen atoms.
• Application: Prevalent in many organic compounds and is key to understanding molecular shapes.

sp2 hybridization

The process of sp2 hybridization occurs when one s orbital mixes with two p orbitals to create three sp2 hybrid orbitals. Each sp2 hybrid orbital has 33.3% s character and 66.7% p character.
These orbitals form a planar trigonal shape with a bond angle of around 120 degrees. The remaining un-hybridized p orbital forms a pi bond, often seen in double-bonded structures.
In compound II, the carbon atoms in the double bond involve such hybridization. Specifically, these carbons form a planar geometry, showcasing the characteristic setup of double bonds.

• Common in alkenes, where the presence of double bonds between carbons is a marker of sp2 hybridization.
• Example: Ethene (C2H4) has each carbon atom sp2 hybridized, participating in a sigma bond with another carbon and two hydrogen atoms.

sp hybridization

Sp hybridization involves the mixing of one s orbital with one p orbital, forming two sp hybrid orbitals. These orbitals have a linear geometry with bond angles of 180 degrees, signifying an equal 50% s and 50% p character.
This hybridization allows the atom to form a triple bond, characteristic of alkynes. Compound III illustrates this, particularly in the carbon involved in a triple bond, exhibiting sp hybridization.

• Sp hybridization is usually seen in molecules with triple bonds, like acetylene (C2H2), where each carbon uses an sp hybrid orbital to overlap with hydrogen and another carbon atom.
• Due to the linear geometry, compounds with sp hybridized carbons often appear in linear shapes.