Problem 82 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following represents the given mode of hybridization \(s p^{2}-s p^{2}-s p-\) sp from left to right? (a) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C} \equiv \mathrm{CN}\) (b) \(\mathrm{CH} \equiv \mathrm{C}-\mathrm{C} \equiv \mathrm{N}\) (c) \(\mathrm{CH}_{2}=\mathrm{C}=\mathrm{C}=\mathrm{CH}_{2}\) (d) \(\mathrm{CH}_{2}\)

Step-by-Step Solution

Answer

Option (a) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C}\equiv\mathrm{CN}\) follows the hybridization pattern.

Step 1: Understand the problem

We are given a mode of hybridization that follows the pattern \(sp^2-sp^2-sp-sp\). We need to identify which chemical structure from the given options represents this pattern from left to right.

Step 2: Analyze each option

Let's analyze each given molecule to find the hybridization at each carbon atom:(a) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C}\equiv\mathrm{CN}\)- \(\mathrm{CH}_2\) is \(sp^2\) due to the double bond.- \(\mathrm{CH}\) is \(sp^2\) because it is doubly bonded.- The first \(\mathrm{C}\) in \(\mathrm{C}\equiv\mathrm{CN}\) is triple bonded, making it \(sp\).- \(\mathrm{N}\) is triple bonded, contributing a lone pair, maintaining \(sp\) hybridization.(b) \(\mathrm{CH}\equiv\mathrm{C}-\mathrm{C}\equiv\mathrm{N}\)- The first \(\mathrm{C}\) is \(sp\) due to the triple bond.- The second \(\mathrm{C}\) is also \(sp\) due to its triple bond with the first \(\mathrm{C}\).(c) \(\mathrm{CH}_{2}=\mathrm{C}=\mathrm{C}=\mathrm{CH}_{2}\)- All \(\mathrm{Cs}\) are \(sp^2\) because they form double bonds.(d) \(\mathrm{CH}_{2}\)- \(\mathrm{C}\) in \(\mathrm{CH}_{2}\) is \(sp^3\) since it forms four single bonds.

Step 3: Compare hybridization

The problem requires identifying the sequence of hybridization \(sp^2-sp^2-sp-sp\). By looking at each option, only option (a) fits the specific hybridization pattern described from left to right: from \(sp^2\) in \(\mathrm{CH}_2\), to \(sp^2\) in \(\mathrm{CH}\), then \(sp\) in the first \(\mathrm{C}\) of \(\mathrm{C}\equiv\mathrm{CN}\), and finally \(sp\) in \(\mathrm{N}\).

Step 4: Conclusion

Thus, the structure \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C}\equiv\mathrm{CN}\) satisfies the given hybridization sequence of \(sp^2-sp^2-sp-sp\).

Key Concepts

sp2 hybridization

Hybridization refers to the concept where atomic orbitals mix to form new, hybrid orbitals suitable for pairing electrons to form chemical bonds in molecules.
In particular, sp2 hybridization happens when one 2s orbital and two 2p orbitals mix together to form three equivalent sp2 hybrid orbitals.
This type of hybridization is typically seen in molecules where the central atom forms three sigma bonds, often including a double bond.

• Each sp2 hybrid orbital has a 120-degree angle of separation from others, which creates a trigonal planar shape.
• This is common in alkenes, such as ethene (\(\mathrm{C}_2\mathrm{H}_4\)).

For example, in ethene, each carbon atom uses sp2 hybridized orbitals to form a sigma bond with two hydrogen atoms and a sigma bond with the other carbon atom.
The remaining unhybridized 2p orbital forms the pi bond, which is part of the double bond between the carbon atoms.

sp hybridization

Sp hybridization occurs when one 2s orbital and one 2p orbital combine to create two new equivalent sp hybrid orbitals.
These orbitals are oriented 180 degrees apart, forming a linear shape.
This occurs in molecules with linear geometry, involving two sigma bonds, such as in molecules with triple bonds or two double bonds.

• Sp hybridization is seen in alkynes like acetylene (\(\mathrm{C}_2\mathrm{H}_2\)), where each carbon atom is sp hybridized.
• Here, the carbons form a triple bond, comprising one sigma bond and two pi bonds.

In acetylene, each carbon atom uses an sp hybrid orbital to form a sigma bond with hydrogen and another sigma bond with the other carbon atom.
The remaining two unhybridized 2p orbitals form two pi bonds, creating the characteristic triple bond.

chemical bonding

Chemical bonding is a fundamental concept in chemistry, explaining how atoms come together to form molecules.
There are several types of bonds, including covalent, ionic, and metallic bonds, each having unique properties and occurring under different circumstances.

• Covalent bonds are formed when atoms share electrons, leading to the formation of molecules like water (\(\mathrm{H}_2\mathrm{O}\)).
• Ionic bonds result from the transfer of electrons from one atom to another, as seen in sodium chloride (\(\mathrm{NaCl}\)).
• Metallic bonds involve a "sea" of electrons that are shared collectively among metal atoms, which accounts for the conductivity and malleability of metals.

Understanding chemical bonds helps us predict molecular structures, determine the angles between bonds, and understand the reactivity of substances.

triple bond

A triple bond is a strong chemical bond involving three pairs of electrons between two atoms, most commonly seen in carbon-nitrogen (as cyanide) or carbon-carbon bonds (as in alkynes).
It consists of one sigma and two pi bonds.
One example of a triple bond is in nitrogen gas (\(\mathrm{N}_2\)), where the three bonds make it very stable and inert under normal conditions.

• Triple bonds are shorter and stronger than single and double bonds.
• They can be found in organic molecules like acetylene (\(\mathrm{C}_2\mathrm{H}_2\)), where the carbon atoms are linked by a triple bond.

In molecules with triple bonds, the atoms involved often exhibit sp hybridization due to the need to share three pairs of electrons through one sigma and two pi bonds.

double bond

Double bonds consist of one sigma bond and one pi bond between two atoms.
This type of bond is commonly seen in alkenes, such as ethene (\(\mathrm{C}_2\mathrm{H}_4\)).
Double bonds are stronger and shorter than single bonds but less so than triple bonds.

• They provide the molecule with a planar structure due to the sp2 hybridization of the involved atoms.
• Double bonds restrict rotation, unlike single bonds, affecting molecular geometry and chemical reactivity.

In organic chemistry, the presence of a double bond can influence the chemical behavior of compounds, as they are often sites of chemical reactions, like addition reactions, where new atoms or groups are added to the bonds.