See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the substrate stereochemistry: The starting material is a cyclohexane with substituents at C1 (CH3, wedge/up), C2 (Br, bold wedge/up), and C3 (CH3, wedge/up). This means C1-CH3, C2-Br, and C3-CH3 are all on the same face (all cis to each other), making this the cis,cis-1,2,3 arrangement: specifically (1R,2R,3S) or equivalent — the key point is that the 1-CH3, 2-Br, and 3-CH3 are all on the same side of the ring. Step 2 - E2 requirement: E2 elimination requires an anti-periplanar arrangement between the H being removed and the leaving group (Br). In a cyclohexane ring, anti-periplanar means the H and Br must both be axial (diaxial relationship). This requires the molecule to adopt a chair conformation where Br is axial and there exists an adjacent axial H. Step 3 - Analyze the chair conformations: With all three substituents (C1-CH3, C2-Br, C3-CH3) cis to each other on the same face, in one chair conformation all three are axial, and in the other all three are equatorial. - If Br at C2 is axial: then C1-CH3 and C3-CH3 are also axial. For E2, we need an axial H on C1 or C3 anti to Br. But C1 has CH3 (axial) — no axial H at C1. C3 has CH3 (axial) — no axial H at C3. Therefore, there is NO axial H anti-periplanar to the axial Br. - If Br at C2 is equatorial: Br cannot participate in E2 from equatorial position. Step 4 - Conclusion: In neither chair conformation is there a viable anti-periplanar H–C–C–Br arrangement for E2 elimination. All adjacent carbons bearing H have their H's equatorial when Br is axial, or Br itself is equatorial. The geometric requirement for E2 (anti-periplanar diaxial H and Br) cannot be satisfied. Step 5 - Why other options fail: - Option (a) and (b) would require successful E2 elimination, which cannot occur due to the stereochemical constraint described above. - Option (c) is a substitution (SN2/SN1) product; NaOCH3 is a strong, bulky base that favors elimination, but more importantly E2 is specified and the conditions strongly favor E2. However, even SN2 could theoretically occur, but the question specifies E2 reaction and no E2 product is geometrically possible. - Since E2 cannot proceed due to the absence of any anti-periplanar H relative to Br in either chair conformation, no elimination product forms. Therefore, the correct answer is D.