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NEET levelSingle correct optionDifficulty 1 of 3o3009

Which of the following is the best leaving group?

A $OH X^{-}$
B $NH X_{2} X^{-}$
C $CH X_{3} O X^{-}$
Dp-toluenesulfonate ion, $CH X_{3} - C X_{6} H X_{4} - SO X_{3} X^{-}$

Answer: D

A good leaving group is the conjugate base of a strong acid, i.e. a weak base that is stabilised by delocalisation. p-Toluenesulfonic acid is a strong acid (pKa about

- 3

), while water, ammonia and methanol are very weak acids, so their conjugate bases are poor leaving groups.

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