Question

In the reaction sequence shown below, what is the mass (in grams) of product (C) formed?

Hint:

When the given mass equals molar mass, the substance is exactly one mole — product mass equals its molar mass if stoichiometry is 1:1.

Answer 1

Correct Answer: 228

Alternative Method (Functional Group Tracking & Stoichiometry Approach):

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The problem involves a sequence of reactions starting from a known aromatic compound. Rather than identifying each intermediate separately, we track how the functional groups change on the aromatic ring and apply stoichiometry at the end.

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Step 1: Identify the starting compound and moles used

The given compound has molar mass 137 g mol⁻¹, which corresponds to p-nitrotoluene (C₇H₇NO₂).

Given mass = 137 g ⇒ number of moles = 1 mole

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Step 2: Reduction of nitro group

Sn/HCl selectively reduces the −NO₂ group to an −NH₂ group without affecting the methyl group on the ring.

Thus, the aromatic ring now contains:

−CH₃ and −NH₂ at para positions

This compound is p-toluidine.

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Step 3: Protection of amine group

Acetic anhydride converts the reactive −NH₂ group into an −NHCOCH₃ group (acetamide), preventing excessive bromination.

The ring now contains:

−CH₃ and −NHCOCH₃

This compound is p-methylacetanilide.

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Step 4: Electrophilic bromination

Both −CH₃ and −NHCOCH₃ are ortho–para directing groups. However, the para positions are already occupied.

Therefore, bromination occurs at an ortho position relative to the activating groups, leading to a mono-brominated product.

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Step 5: Molecular formula of final compound

The final compound contains:

• 9 carbon atoms
• 10 hydrogen atoms
• 1 nitrogen atom
• 1 oxygen atom
• 1 bromine atom

Final molecular formula = C₉H₁₀BrNO

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Step 6: Molar mass and final mass calculation

Molar mass of final compound:

9×12 + 10×1 + 14 + 16 + 80 = 228 g mol⁻¹

Since the reaction sequence proceeds on a 1 : 1 molar basis and we started with 1 mole:

Mass of compound (C) formed = 228 g

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Final Answer:

228 g