The sequence involves three major organic reactions: the Wurtz reaction (coupling), Aromatization (alkane to arene), and Friedel-Crafts Acylation. We need to determine the structure of the final product Z and count the types of carbon atoms.
Step 2: Detailed Explanation:
1. Step 1 (Wurtz Reaction): The reactant shown is n-propyl bromide (\( \text{C}_3\text{H}_7\text{Br} \)).
\( 2\text{CH}_3\text{CH}_2\text{CH}_2\text{Br} + 2\text{Na} \xrightarrow{\text{dry ether}} \text{n-Hexane (X)} \)
Product X is n-Hexane (\( \text{C}_6\text{H}_{14} \)).
2. Step 2 (Aromatization): When n-alkanes with 6 or more carbons are heated with oxide catalysts like \( \text{Cr}_2\text{O}_3 \) at high temperature, they cyclize and dehydrogenate to form aromatic rings.
\( \text{n-Hexane} \xrightarrow{\text{Cr}_2\text{O}_3, 773\text{K}} \text{Benzene (Y)} \)
Product Y is Benzene (\( \text{C}_6\text{H}_6 \)).
3. Step 3 (Friedel-Crafts Acylation): Benzene reacts with acetyl chloride in the presence of anhydrous \( \text{AlCl}_3 \).
\( \text{C}_6\text{H}_6 + \text{CH}_3\text{COCl} \xrightarrow{\text{anhy. AlCl}_3} \text{Acetophenone (Z)} \)
Structure of Acetophenone: A benzene ring attached to a \( -\text{COCH}_3 \) group. Formula: \( \text{C}_6\text{H}_5\text{COCH}_3 \).
Counting Carbons in Z (Acetophenone):
Benzene Ring: Contains 6 carbons. All are \( sp^2 \) hybridized.
Carbonyl Carbon (\( \text{C=O} \)): Double bonded to oxygen. It is \( sp^2 \) hybridized.
Methyl Carbon (\( \text{-CH}_3 \)): Single bonded to carbonyl carbon. It is \( sp^3 \) hybridized.
Total \( sp^2 \) carbons (\( b \)) = \( 6 (\text{ring}) + 1 (\text{carbonyl}) = 7 \).
Total \( sp^3 \) carbons (\( a \)) = \( 1 (\text{methyl}) \).
Value of \( a + b = 1 + 7 = 8 \).
Step 3: Final Answer:
