Problem 102 - A Complete Resource Book in Chemistry for JEE Main

Question

Identify the correct sequence of increasing number of \(\pi\) bonds in the structures of the following molecules 1\. \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6}\) 2\. \(\mathrm{H}_{2} \mathrm{SO}_{3}\) 3\. \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{5}\) (a) \(1,2,3\) (b) \(2,3,1\) (c) \(2,1,3\) (d) \(1,3,2\)

Step-by-Step Solution

Answer

Option (c) 2, 1, 3 is the correct sequence of increasing π bonds.

Step 1: Analyze Structure of H2S2O6

H2S2O6 is often referred to as dithionic acid. In this structure, each sulphur is bonded to two oxygen atoms with single bonds, and one sulphur is bonded to the other with a single bond as well. There are two double-bonded oxygen atoms to each sulphur, giving us 2 π bonds totally.

Step 2: Analyze Structure of H2SO3

H2SO3 is known as sulfurous acid. The sulfur atom is typically bonded to two hydroxide groups and one oxygen atom through a double bond, leading to one π bond in total.

Step 3: Analyze Structure of H2S2O5

H2S2O5 is known as disulfurous acid or pyrosulfurous acid. It contains an S-S bond and each sulphur is bonded to two double-bonded oxygen atoms. This results in 3 π bonds.

Step 4: Compare and Order the Molecules

Now we compare the number of π bonds in each molecule. H2SO3 has 1 π bond, H2S2O6 has 2 π bonds, and H2S2O5 has 3 π bonds. Therefore, the increasing order is H2SO3 (1 π bond), H2S2O6 (2 π bonds), and H2S2O5 (3 π bonds).

Step 5: Match with Options

The correct sequence based on the increasing number of π bonds is 2, 1, 3. Comparing this with the given options, we find that option (c) corresponds to this order.

Key Concepts

Pi Bonds

Pi bonds are a type of covalent bond that occurs when orbitals overlap in a side-by-side manner. These bonds are significant because they contribute to the double or triple bonds in molecules and influence the molecule's properties like bonding and stability.

• Pi bonds occur in addition to a sigma bond in double or triple bonds.
• They are typically less strong compared to sigma bonds.
• Pi bonds restrict the rotation of bonded atoms, affecting the molecule's shape.

In the exercise problem, examining the number of pi bonds gave us an insight into the reactivity and structure of different sulfur compounds.

Structural Analysis

Structural analysis in chemistry involves examining how atoms are arranged and connected in a molecule. This is critical in understanding the molecule's characteristics and behavior.

• This involves looking at both atom connectivity and the types of bonds present, such as single, double, or triple bonds.
• Differences in structure can result in variations in chemical properties or reactivity.

In the original solution, we analyzed the molecular structure of each compound to determine the number of pi bonds, which requires accurately drawing and interpreting molecule diagrams.

Sulfur Compounds

Sulfur compounds are crucial in many chemical and biological processes. They often form complex structures due to sulfur's ability to make multiple bonds.

• Sulfur can expand its valence shell, unlike some other elements like oxygen or nitrogen.
• It can form bonds with a variety of elements including oxygen and hydrogen.

The exercise involved understanding sulfur's ability to double bond with oxygen, which impacts the compound's stability and reactivity significantly.

Molecular Structure

The molecular structure is how molecules are built, showing the arrangement of atoms in space. It is fundamental to determining how a molecule interacts chemically.

• Understanding molecular geometry can help predict molecule polarity and reactivity.
• Molecules can be simple linear forms or complex 3D shapes.

In this context, examining sulfur compounds showed us the bond angles and electron distribution crucial for predicting the number of pi bonds.

Dithionic Acid

Dithionic acid (\(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6}\)) is a sulfur-containing acid. Its structure includes two sulfur atoms bonded to each other and to oxygen atoms.

• Each sulfur in dithionic acid is double-bonded to two oxygens, contributing to the pi bonds.
• Recognizing these bonds was crucial for our exercise solution where we identified 2 pi bonds.

This acid is a good case study of sulfur's ability to form extended structures beyond simpler acids.

Sulfurous Acid

Sulfurous acid (\(\mathrm{H}_{2} \mathrm{SO}_{3}\)) is another sulfur-bearing acid, where sulfur bonds with hydroxide groups and one oxygen.

• The presence of a single double bond to oxygen accounts for its one pi bond.
• Understanding its structure helps in grasping its lower reactivity compared to more complex sulfur compounds.

This showcases basic acid structure and how sulfur creates varied bond environments.

Pyrosulfurous Acid

Pyrosulfurous acid (\(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{5}\)), also known as disulfurous acid, consists of two sulfur atoms linked together.

• Each sulfur connects with two double-bonded oxygens, forming 3 pi bonds overall.
• This complex bonding pattern shows how sulfur's versatility affects compound properties and led to it having the highest pi bond count in our comparison.

Understanding this acid demonstrates sulfur compounds' complexity, making them ideal for chemical studies.