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JEE Main levelOne or more correct optionsDifficulty 2 of 3o3070

Consider 1-bromobicyclo[2.2.1]heptane, in which the bromine is on a bridgehead carbon. Select the correct statements.

  1. AWith in acetone it reacts faster than 2-bromopropane.
  2. BIt is also very unreactive towards SN1 because the bridgehead carbocation cannot become planar.
  3. CIt cannot undergo SN2 because the backside of the C-Br bond lies inside the cage and is shielded by the carbon skeleton, so inversion is impossible.
  4. DBeing tertiary, it ionises faster than tert-butyl bromide in ethanol.

Answer: B, C

SN2 needs attack at 180 degrees to the leaving group, which is impossible at a bridgehead whose rear side points into the cage. SN1 would need a planar carbocation, and the bicyclic framework cannot flatten the bridgehead carbon, so ionisation is also extremely slow. Hence the first two statements are correct and the last two are wrong.
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