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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o4248

The single stereoisomer shown is treated with sodium ethoxide in ethanol (E2). Select all correct statements.

  1. AThe major alkene is (Z)-3-methylpent-2-ene.
  2. B3-Methylpent-1-ene is formed as a minor constitutional isomer.
  3. CThe major alkene is (E)-3-methylpent-2-ene.
  4. DThe diastereomer of the compound shown at C-3 would give the opposite alkene geometry as its major product.

Answer: A, B, D

The compound is (2S,3R)-2-bromo-3-methylpentane. Only one conformer places the C-3 hydrogen anti to bromine, and in it the C-2 methyl and the C-3 ethyl groups are cis, giving the Z alkene as the major Saytzeff product, with a little terminal 3-methylpent-1-ene from the C-1 hydrogens. The anti requirement makes the reaction stereospecific, so the (2S,3S) diastereomer gives the E alkene.
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