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. \(\mathrm{CH}_{3} \cdot \mathrm{CH}=\mathrm{CH}^{2} \cdot \mathrm{CH}_{3}\) III. \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C}=\mathrm{CH}\) 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: Identify the hybridization of each carbon atom in compound I

Compound I is \( \mathrm{CH}_{3} \cdot \mathrm{CH}_{2} \cdot \mathrm{CH}_{2} \cdot \mathrm{CH}_{3} \), which is butane. Each carbon atom is attached to either hydrogen or another carbon with only single bonds. Therefore, all carbon atoms in butane are \( \text{sp}^3 \) hybridized.

Step 2: Identify the hybridization of each carbon atom in compound II

Compound II is \( \mathrm{CH}_{3} \cdot \mathrm{CH} = \mathrm{CH} \cdot \mathrm{CH}_{3} \), which is 2-butene. The terminal \(\mathrm{CH}_{3} \) groups have \( \text{sp}^3 \) hybridization. The carbon atom in \(\mathrm{CH} = \mathrm{CH} \) has \( \text{sp}^2 \) hybridization due to the double bond.

Step 3: Identify the hybridization of each carbon atom in compound III

Compound III is \( \mathrm{CH}_{2} = \mathrm{CH} - \mathrm{C} = \mathrm{CH} \), acetylene. The two end carbon atoms \(\mathrm{CH}_{2} = \mathrm{CH} \) have \( \text{sp}^2 \) hybridization, while the internal carbon atom connected by a triple bond \(- \mathrm{C} = \mathrm{CH} \) is \( \text{sp} \) hybridized.

Step 4: Identify the hybridization of each carbon atom in compound IV

Compound IV is \( \mathrm{CH}_{2} = \mathrm{CH}_{2} \), which is ethylene. Both carbon atoms involved in the double bond are \( \text{sp}^2 \) hybridized.

Step 5: Determine which compound has more than one type of hybridization

Based on the analysis, compound II has \( \text{sp}^3 \) and \( \text{sp}^2 \) hybridization and compound III has \( \text{sp} \) and \( \text{sp}^2 \) hybridization for different carbon atoms. Therefore, compounds II and III contain more than one type of hybridization.

Key Concepts

Butane

Butane is a simple organic molecule with the chemical formula \( \mathrm{C}_{4}\mathrm{H}_{10} \). It is a saturated hydrocarbon, meaning it contains only single bonds between its carbon atoms. This structure allows butane to assume an open-chain aliphatic configuration.
Each carbon in butane forms four sigma bonds, one with each of the three hydrogen atoms and the fourth with a neighboring carbon atom.
In such a setup, the hybridization of these carbon atoms is \(\text{sp}^3\), which results from one \(s\) orbital and three \(p\) orbitals combining to create four equal-energy hybrid orbitals. These \(\text{sp}^3\) hybridized orbitals allow for a tetrahedral shape around each carbon, resulting in an angle of approximately 109.5 degrees between the bonds.
Key points about butane hybridization:

• All carbon atoms are \(\text{sp}^3\) hybridized.
• Tetrahedral geometry around each carbon atom.
• Composed of only sigma bonds, granting butane flexibility.

2-Butene

2-butene is an unsaturated hydrocarbon with the formula \( \mathrm{C}_{4}\mathrm{H}_{8} \), distinguished by having a double bond between two of its carbon atoms.
This organic compound can exist in two geometric isomers, known as cis-2-butene and trans-2-butene.
The double bond impacts the hybridization of the involved carbon atoms. Specifically:

• The terminal \(\mathrm{CH}_3\) groups in \(\mathrm{CH}_{3} \cdot \mathrm{CH} = \mathrm{CH} \cdot \mathrm{CH}_{3}\) are \(\text{sp}^3\) hybridized.
• The carbons involved in the double bond \((\mathrm{CH} = \mathrm{CH})\) are \(\text{sp}^2\) hybridized.

This different hybridization ensures a planar structure for the double bond region, with a bond angle of approximately 120 degrees, a characteristic of \(\text{sp}^2\) hybridization.
The presence of both \(\text{sp}^3\) and \(\text{sp}^2\) hybridized carbon atoms means that the compound has both the flexibility of \(\text{sp}^3\) and the rigidity of \(\text{sp}^2\) components.

Acetylene

Acetylene is a simple alkyne with the formula \( \mathrm{C}_{2}\mathrm{H}_{2} \), exemplifying the characteristics of \(\text{sp}\) hybridization. It features a triple bond between the two carbon atoms, making it a highly unsaturated hydrocarbon.
Within acetylene:

• Each carbon atom is \(\text{sp}\) hybridized, resulting from the combination of one \(s\) and one \(p\) orbital to form two \(sp\) hybrid orbitals.
• These \(\text{sp}\) orbitals form sigma bonds with one hydrogen and the other carbon atom.
• The remaining two \(p\) orbitals on each carbon form two \(\pi\) bonds, leading to the triple bond.

The linear configuration of acetylene, attributed to its \(\text{sp}\) hybridization, results in a bond angle of 180 degrees. This linearity and the multiple bonding between carbons provide acetylene with its unique properties.
An internal carbon in extended acetylene chains, like in \(\mathrm{CH}_2=\mathrm{CH}-\mathrm{C} \equiv \mathrm{CH}\), will be \(\text{sp}\) hybridized due to triple bonding, illustrating the variety of potential configurations.

Chemical Bonding

Chemical bonding refers to the attractive forces that hold atoms together in a compound. In organic molecules like butane, 2-butene, and acetylene, the types of bonds greatly influence the structure and properties of the compound.
The main types of chemical bonding in hydrocarbons include:

• Sigma (\(\sigma\)) bonds, formed by the overlap of two orbitals directly between two atoms, found in all these compounds.
• Pi (\(\pi\)) bonds, arising from the sidewise overlap of \(p\) orbitals, present in 2-butene and acetylene due to their double and triple bonds, respectively.

Various types of hybridization (\(\text{sp}^3\), \(\text{sp}^2\), and \(\text{sp}\)) illustrate different bond angles and molecular shapes:

• \(\text{sp}^3\): Tetrahedral, 109.5 degrees.
• \(\text{sp}^2\): Trigonal planar, 120 degrees.
• \(\text{sp}\): Linear, 180 degrees.

Understanding how chemical bonds form and influence molecular structure is crucial for decoding the behavior and reactivity of organic compounds.

Carbon Compounds

Carbon compounds are fundamental to the field of organic chemistry, with carbon's ability to form diverse structures due to its tetravalency.
The variety in carbon bonding arises from its ability to hybridize into different orbitals:

• \(\text{sp}^3\) hybridization leads to a three-dimensional tetrahedral geometry, typical in saturated hydrocarbons like butane.
• \(\text{sp}^2\) hybridization gives rise to planar structures, as seen in compounds like 2-butene and ethylene.
• \(\text{sp}\) hybridization results in linear molecules, exemplified by acetylene.

Carbon compounds range from simple molecules like methane to complex macromolecules like proteins and synthetic polymers. This diversity stems from carbon’s unique ability to form stable bonds with other carbon atoms and various elements, resulting in a limitless array of structures and functions. The study and understanding of these compounds are pivotal to advancements in both industrial applications and biological sciences.