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JEE Main levelSingle correct optionDifficulty 2 of 3g2116

Take $p K_{a} (H X_{2} CO X_{3}) = 6.4$ . Which of the following reactions does NOT proceed appreciably in the forward direction?

A $CH X_{3} COOH + NaHCO X_{3} CH X_{3} COONa + H X_{2} CO X_{3}$
B $C X_{6} H X_{5} OH + NaHCO X_{3} C X_{6} H X_{5} ONa + H X_{2} CO X_{3}$
C $C X_{6} H X_{5} OH + NaOH C X_{6} H X_{5} ONa + H X_{2} O$
D $HC \equiv CH + NaNH X_{2} HC \equiv CNa + NH X_{3}$

Answer: B

Take

p K_{a}

: phenol 10.0, acetic acid 4.76, water 15.7, acetylene 25, ammonia 38. Phenol with

HCO X_{3} X^{-}

has

lo g K = 6.4 - 10.0 = - 3.6

, so it lies far to the left. The other three have

lo g K

of

+ 1.6

,

+ 5.7

and

+ 13

, all forward.

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