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: Understanding Hybridization

Hybridization is the concept of mixing atomic orbitals to form new orbitals, which correspond to the geometry observed in molecules. The common types are \( sp^3 \), \( sp^2 \), and \( sp \) hybridizations, which are associated with single, double, and triple bonds, respectively.

Step 2: Analyze compound I

Compound I, \(\mathrm{CH}_{3} \, \mathrm{CH}_{2} \, \mathrm{CH}_{2} \, \mathrm{CH}_{3}\), is a straight-chain alkane with only single bonds. Each carbon atom in this molecule exhibits \( sp^3 \) hybridization.

Step 3: Analyze compound II

Compound II, \(\mathrm{CH}_{3} \, \mathrm{CH}^{2}=\mathrm{CH}^{2} \, \mathrm{CH}_{3}\), has a double bond. Here, the carbon atoms in the \(\mathrm{CH}_{3}\) groups are \( sp^3 \) hybridized, while the carbon atoms involved in the double bond \(\mathrm{CH}^{2}=\mathrm{CH}^{2}\) are \( sp^2 \) hybridized. Thus, this compound has both \( sp^3 \) and \( sp^2 \) hybridized carbons.

Step 4: Analyze compound III

Compound III, \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C} \equiv \mathrm{CH}\), has a mix of double and triple bonds. \(\mathrm{CH}_{2}=\) has \( sp^2 \) hybridization, and \(\mathrm{C} \equiv \mathrm{CH}\) has \( sp \) hybridization. Thus, this molecule involves both \( sp^2 \) and \( sp \) hybridized carbon atoms.

Step 5: Analyze compound IV

Compound IV, \(\mathrm{CH}_{2}=\mathrm{CH}_{2}\), has a double bond, with each carbon being \( sp^2 \) hybridized.

Step 6: Determine the compounds with more than one hybridization

From the analysis, compound II shows both \( sp^3 \) and \( sp^2 \) hybridization, and compound III shows both \( sp^2 \) and \( sp \) hybridization. Therefore, these compounds have more than one type of hybridization for carbon atoms.

Key Concepts

sp3 hybridization

In organic chemistry, sp3 hybridization is a fundamental concept that helps explain the geometry of molecules with single bonds. When sp3 hybridization occurs, one s orbital combines with three p orbitals from the same atom to form four equivalent hybrid orbitals. Each sp3 hybrid orbital has 25% s character and 75% p character. This type of hybridization results in a tetrahedral shape around the central atom, with bond angles of approximately 109.5 degrees.
For example, in the compound \(\mathrm{CH}_{3} \cdot \mathrm{CH}_{2} \cdot \mathrm{CH}_{2} \cdot \mathrm{CH}_{3}\), often referred to as an alkane, each carbon atom is involved in single bonds and exhibits sp3 hybridization. These single sigma bonds allow for free rotation around the bond axis, contributing to the flexibility of alkanes.
Key aspects of sp3 hybridization include:

• Tetrahedral geometry.
• Single bonds formed via sigma bonds.
• Commonly seen in alkanes and other saturated hydrocarbons.

sp2 hybridization

sp2 hybridization occurs when one s orbital mixes with two p orbitals on the same atom, resulting in three equivalent sp2 hybrid orbitals. These hybrid orbitals account for 33% s character and 67% p character. The unhybridized p orbital remains and is often involved in forming pi bonds. This results in a trigonal planar shape with bond angles of about 120 degrees.
In the compound \(\mathrm{CH}_3 \cdot \mathrm{CH}^{2}=\mathrm{CH}^{2} \cdot \mathrm{CH}_3\), the sp2 hybridization is observed at the carbon atoms involved in the double bond. These double bonds consist of one sigma bond and one pi bond, the latter formed from the overlap of p orbitals.
Characteristics of sp2 hybridization include:

• Trigonal planar geometry around the carbon.
• Formation of both sigma and pi bonds.
• Observed in alkenes, which have double bonds.

sp2 hybridized compounds often contribute to the rigidity of organic frameworks because rotation around double bonds is restricted due to the pi bond.

sp hybridization

In sp hybridization, one s orbital mixes with one p orbital from the same atom, forming two equivalent hybrid orbitals. Each sp hybrid orbital contains 50% s character and 50% p character, which gives this hybridization linear geometry with bond angles of 180 degrees. The remaining two unhybridized p orbitals are available for forming pi bonds.
In the compound \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C} \equiv \mathrm{CH}\), the sp hybridization can be observed in the carbon atoms involved in triple bonds. These triple bonds consist of one sigma bond and two pi bonds. The presence of pi bonds makes the compound with such hybridization relatively rigid and linear.
Notable aspects of sp hybridization include:

• Linear geometry.
• Common in alkynes, which feature triple bonds.
• Presence of multiple pi bonds creating rigidity and shorter bond lengths.

Because of their linear shape and multiple pi bonds, sp hybridized molecules often exhibit high strength and reduced rotation, which imparts unique chemical and physical properties.