Question

In the compound, \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{C} \equiv \mathrm{CH}\), the \(\mathrm{C}_{2}-\mathrm{C}_{3}\) bond is of the type (a) \(\mathrm{sp}-\mathrm{sp}^{2}\) (b) \(\mathrm{sp}^{3}-\mathrm{sp}^{3}\) (c) \(\mathrm{sp}-\mathrm{sp}^{3}\) (d) \(\mathrm{sp}^{2}-\mathrm{sp}^{3}\)

Short answer

(d) \( \mathrm{sp}^{2}-\mathrm{sp}^{3} \)

Step-by-step solution

Identify the structure of the compound

The compound is a hydrocarbon with the structure \( \mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{C} \equiv \mathrm{CH} \). This is a linear hydrocarbon chain with a mix of single, double, and triple bonds, specifically an alkyne group at the end.

Locate the position of C2 and C3

In the given compound, the carbon atoms can be numbered sequentially. Starting from the left (near the double bond): \( \mathrm{C}_{1}=\mathrm{CH}_{2}=\mathrm{C}_{2}=\mathrm{CH}-\mathrm{C}_{3}=\mathrm{CH}_{2}-\mathrm{C}_{4}=\mathrm{CH}_{2}-\mathrm{C}_{5} \equiv \mathrm{CH} \). Therefore, \( \mathrm{C}_{2} \) is part of the double bond \( \mathrm{CH}_{2}=\mathrm{CH} \) and \( \mathrm{C}_{3} \) is \( \mathrm{CH}_{2} \).

Identify hybridization of each carbon atom

\( \mathrm{C}_{2} \) is connected to \( \mathrm{C}_{1} \) by a double bond, making \( \mathrm{C}_{2} \) \( \mathrm{sp}^{2} \) hybridized (trigonal planar). \( \mathrm{C}_{3} \), being \( \mathrm{CH}_{2} \) and single-bonded, is \( \mathrm{sp}^{3} \) hybridized (tetrahedral).

Determine the bond type

The \( \mathrm{C}_{2} \) to \( \mathrm{C}_{3} \) bond involves an \( \mathrm{sp}^{2} \) hybridized carbon and an \( \mathrm{sp}^{3} \) hybridized carbon. Therefore, the bond type is \( \mathrm{sp}^{2}-\mathrm{sp}^{3} \).

Key concepts

Hybridization

Hybridization in chemistry is a concept that describes the mixing of atomic orbitals to form new hybrid orbitals. These hybrid orbitals are important in explaining the geometry of molecular structures. A key idea is that the atomic orbitals, such as s, p, and d, combine to generate hybrid orbitals that have different shapes and energy levels.

For organic compounds, especially hydrocarbons, hybridization helps determine how atoms connect and shape the molecule.

• sp Hybridization: This involves the mixing of one s and one p orbital, resulting in two equivalent linear orbitals. This is typical in carbon atom cases with triple bonds, such as in alkynes.
• sp² Hybridization: Here, one s orbital mixes with two p orbitals. This creates three equivalent hybrid orbitals, which is common in double-bonded carbons, leading to a trigonal planar geometry.
• sp³ Hybridization: The mixing of one s orbital with three p orbitals results in four equivalent hybrid orbitals, corresponding to a tetrahedral geometry. This is seen in carbons with four single bonds.

Understanding hybridization is crucial for determining the bonding and 3D layout of molecules, which ultimately influences their chemical behavior.

Hydrocarbon Structure

Hydrocarbons are compounds composed exclusively of hydrogen and carbon atoms. They form the foundation of organic chemistry and can vary widely in size and complexity. The type of bonds between the carbon atoms—single, double, or triple—dictate the category of the hydrocarbon.

Key categories of hydrocarbons include:

• Alkanes: These are saturated hydrocarbons with single bonds, having sp³ hybridized carbons, and are known for their linear or branched structures.
• Alkenes: Unsaturated hydrocarbons containing at least one double bond, with sp² hybridized carbons, contributing to their planar structure.
• Alkynes: Known for triple bonds, where carbons are sp hybridized and the structure is linear.

Understanding the structure of hydrocarbons involves recognizing these bonds and the spatial arrangement of the atoms, which is crucial for predicting reactivity and properties.

Alkyne Group

The alkyne group is a functional group in hydrocarbons that contains at least one carbon-carbon triple bond. This triple bond is characterized by an sp hybridization state, which arises from the mixing of one s and one p orbital.

As a direct consequence of this hybridization, triple-bonded carbons form linear structures, giving alkynes a distinct shape compared to alkanes and alkenes. For example, in an alkyne like ethyne (acetylene), the molecule appears linear due to the sp hybridization, with two poles of electron density.

Alkynes are unsaturated hydrocarbons, allowing for multiple types of reactions such as hydration, hydrohalogenation, and polymerization. These reactions are paramount in industrial applications, ranging from synthetic manufacturing to producing polymers and other complex molecules.

• Structurally, the presence of a \(-C \equiv C-\) group makes alkynes more reactive than alkanes and allows them to participate in reactions that alter the carbon-carbon bond.
• The linear shape also makes alkynes fit into certain binding sites differently than other hydrocarbons, influencing their chemical reactivity.

Therefore, understanding the nature of the alkyne group is essential for grasping the broader concepts of organic chemistry.