Question

Calculate total number of mass percentage of oxygen in the product.

• A. 10.13
• B. 12.50
• C. 15.38
• D. 18.00

Hint:

Intramolecular Friedel-Crafts acylation creates cyclic ketones. Intramolecular Aldol condensation follows to form cyclic $\alpha,\beta$-unsaturated ketones, provided the ring size is favorable (usually 5 or 6 members). Always use the exact molar mass specified or derived from the specific product structure.

Answer 1

The Correct Option is A

Step 1: The given reaction starts with an acid chloride reacting in presence of $AlCl_3$. This indicates a Friedel–Crafts acylation reaction. Step 2: In presence of $AlCl_3$, acid chloride generates an acylium ion: \[ RCOCl + AlCl_3 \rightarrow RCO^+ + AlCl_4^- \] Step 3: Since the reaction shown in the question leads to a cyclic ketone, the process is an intramolecular Friedel–Crafts acylation. Intramolecular reactions are favored when 5- or 6-membered rings can form. Step 4: Thus, the acid chloride cyclizes to form a cyclic ketone as the intermediate product. Step 5: In the next step, the cyclic ketone is treated with aqueous NaOH and heat. These are standard conditions for an aldol condensation. Step 6: The ketone has $\alpha$-hydrogens, so it forms an enolate ion in basic medium: \[ \text{Ketone} + OH^- \rightarrow \text{Enolate ion} \] Step 7: The enolate attacks the carbonyl carbon intramolecularly, forming a $\beta$-hydroxy ketone. Step 8: On heating, dehydration occurs, producing an $\alpha,\beta$-unsaturated ketone as the final product. Step 9: From the given solution data, the molar mass of the final product is $158\,\text{g/mol}$ and it contains only one oxygen atom. Step 10: Mass of oxygen in one mole of product: \[ =16\,\text{g} \] Step 11: Percentage of oxygen: \[ %O=\frac{16}{158}\times100=10.13% \] Hence, the correct answer is (A) 10.13.