The number of -CH$$_2$$- (methylene) groups in the product formed from the following reaction sequence is _______.

Analyze the Starting Material

The given reactant is an alkene with a straight carbon chain. Let's count the total number of carbons and identify its structure:

• The molecule is oct-4-ene: CH₃-CH₂-CH₂-CH=CH-CH₂-CH₂-CH₃
• It is a symmetrical alkene with 8 carbon atoms.

Step-by-Step Reaction Sequence

Step 1: Ozonolysis (O₃, Zn/H₂O)

Reductive ozonolysis cleaves the carbon-carbon double bond (C=C) and replaces it with carbonyl groups (C=O).

• Symmetrical cleavage of oct-4-ene yields 2 molecules of butanal.
• Molecule formed: 2 × CH₃-CH₂-CH₂-CHO (Butanal)

Step 2: Oxidation (KMnO₄)

Potassium permanganate (KMnO₄) is a strong oxidizing agent that oxidizes aldehydes into carboxylic acids.

• Oxidation of butanal yields butanoic acid.
• Molecule formed: 2 × CH₃-CH₂-CH₂-COOH (Butanoic acid)

Step 3: Kolbe's Electrolysis (NaOH, electrolysis)

Reacting butanoic acid with NaOH forms sodium butanoate (CH₃-CH₂-CH₂-COONa). When subjected to Kolbe's electrolytic decarboxylation, two alkyl radicals dimerize by losing carbon dioxide (CO₂).

• The alkyl radical generated is the propyl radical: •CH₂-CH₂-CH₃
• Two propyl radicals combine: CH₃-CH₂-CH₂- + -CH₂-CH₂-CH₃ ⟶ CH₃-CH₂-CH₂-CH₂-CH₂-CH₃
• Product formed: n-hexane (a straight-chain alkane with 6 carbon atoms).

Step 4: Aromatization (Cr₂O₃, 770 K, 20 atm)

Heating n-hexane in the presence of chromium oxide (Cr₂O₃) catalyst at high temperature and pressure undergoes dehydrogenation and cyclization (aromatization).

• n-hexane converts into Benzene (C₆H₆).
• Product formed: Benzene

Count the Methylene (-CH₂-) Groups in the Final Product

• The final product is Benzene (C₆H₆).
• Structurally, benzene consists of a ring where every single carbon is bonded to one hydrogen atom (-CH- groups).
• There are no saturated methylene (-CH₂-) groups present anywhere in a benzene ring.

Therefore, the number of -CH₂- groups in the final product is 0.