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JEE Advanced levelSingle correct optionDifficulty 3 of 3o4105

The ring of tert-butylchlorocyclohexane is locked with the tert-butyl group equatorial. With in at 298 K, the second-order E2 rate constants are for the cis-1-tert-butyl-4-chlorocyclohexane and for the trans isomer. With , which statement is correct?

  1. AThe cis isomer reacts faster because its chlorine is equatorial;
  2. BThe cis isomer reacts faster because its chlorine is axial in the locked chair;
  3. CThe cis isomer reacts faster because its chlorine is axial;
  4. DThe trans isomer reacts faster because its chlorine is axial;

Answer: B

In the cis-1,4 isomer with tert-butyl equatorial, Cl must be axial, and axial hydrogens on C-2 and C-6 are anti to it, so E2 is fast. In the trans isomer Cl is equatorial in the locked chair and has no anti hydrogen. The ratio is , so (using by mistake gives 7.1).
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