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JEE Main levelSingle correct optionDifficulty 2 of 3g2121

Which base converts a simple ketone such as acetone ( $p K_{a} \approx 19.3$ in water) almost completely into its enolate?

A $NaOH$ (conjugate acid water, 15.7)
B $NaOC X_{2} H X_{5}$ (conjugate acid ethanol, 15.9)
C $LiN (i - C X_{3} H X_{7}) X_{2}$ (LDA; conjugate acid pKa about 36)
D $NaHCO X_{3}$ (conjugate acid $H X_{2} CO X_{3}$ , 6.4)

Answer: C

Complete enolate formation needs the conjugate acid of the base to be much weaker than the ketone (19.3). LDA (about 36) gives

lo g K \approx 17

.

NaOH

(

lo g K = 15.7 - 19.3 = - 3.6

),

NaOEt

(

- 3.4

) and

NaHCO X_{3}

(

- 12.9

) give only a small fraction of enolate.

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