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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o4054

Which of the following statements is/are correct about the E1cB mechanism?

  1. AThe beta-hydrogen should be made acidic by an electron-withdrawing group such as C=O, or .
  2. BA poor leaving group such as or can be lost from the carbanion.
  3. CThe position of the new double bond is decided mainly by the position of the acidifying group, not by Saytzeff stability.
  4. DThe rate is always independent of the concentration of the base.

Answer: A, B, C

E1cB requires a beta-hydrogen made acidic by a group such as C=O, , or CN. Poor leaving groups such as OH and OR can leave from the carbanion. The position of the double bond is fixed by where the acidic hydrogen is, not by alkene stability. The rate depends on the base concentration when carbanion formation is rate-determining.
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