Reactions Of Chromium Compounds

To solve this question, we need to analyze the given chemical reactions step-by-step and determine the products [A] and [B]. Let's go through the reactions:

1. The first reaction is:

In this reaction, potassium dichromate reacts with potassium hydroxide under heat. The product formed, [A], is potassium chromate . This involves a change from the dichromate anion to the chromate anion.

1. The second reaction is:

In this reaction, [A] (which we identified as ) reacts with sulfuric acid . This reaction converts the chromate ion back to the dichromate ion. The product [B] is potassium dichromate, , and potassium sulfate is also formed.

Therefore, the correct products for the reactions are:

• [A]:
• [B]:

Given these deductions, the correctly matched products according to the options provided are:

and

To determine the products [A] and [B] in the given reaction, let's analyze each step:

The initial reactant is chlorobenzene (C₆H₅Cl). The reaction with is typical of a nucleophilic aromatic substitution. Under these harsh conditions, the chlorine atom is replaced by an OH group, forming phenol (C₆H₅OH).

Next, phenol (C₆H₅OH) is oxidized using . This is a classic oxidation reaction where phenol is oxidized to benzoquinone.

So, the products are:

• [A] is phenol (C₆H₅OH)
• [B] is benzoquinone

The correct answer matches the provided option with products , which indicates phenol followed by oxidation to benzoquinone.

Step 1: Understanding the Concept:
The bond length of a covalent bond is inversely proportional to its bond order. A pure double bond is shorter than a bond that has partial single bond character due to resonance or conjugation.

Step 2: Key Formula or Approach:
Analyze the resonance and conjugation in each species:
1. (y) Propanone: Isolated double bond (Bond order ).
2. (x) Benzoquinone-like structure: is in conjugation with the ring system (Bond order ).
3. (z) Acetate ion: is in complete resonance with the other oxygen atom (Bond order ).

Step 3: Detailed Explanation:
In species (y), the carbonyl group is localized, making it a strong double bond with the highest bond order and shortest length.
In species (x), the carbonyl oxygen is conjugated with the cyclohexadiene ring. Resonance slightly reduces the double bond character, increasing the bond length relative to (y).
In species (z), the acetate ion ( ) exhibits equivalent resonance structures where the negative charge is delocalized over both oxygen atoms. The bond order for each C-O bond is exactly 1.5, which is much lower than 2. This results in the longest bond length among the three.
Therefore, the length order is: .

Step 4: Final Answer:
The correct order of bond length is .