Question

The order of `K_(eq)` values for the following keto-enol equilibrium constants is
`CH_(3)-CHO overset(K_(1))hArrCH_(2)=CH-OH`,
`CH_(3)-overset(O)overset(||)(C)-CH_(2)-overset(O)overset(||)(C)-CH_(3)overset(K_(2))hArrCH_(3)-overset(OH)overset(|)(C)=CH-overset(O)overset(||)(C)-CH_(3)`
`{:(" "O" "OH),(" ||"" |"),(CH_(3)-C-CH_(3)overset(K_(3))hArrCH_(2)=C-CH_(3)):}`
A. `K_(1) gt K_(2) gt K_(3)`
B. `K_(2) gt K_(3) gt K_(1)`
C. `K_(2) gt K_(1) gt K_(3)`
D. `K_(1) gt K_(3) gt K_(2)`

Answer 1

Correct Answer - B
In `CH_(3)-overset(O)overset(||)(C)-CH_(2)-overset(O)overset(||)(C)-CH_(3)`, the enol form is stable due to intramolecular H-bonding

Hence enol content maximum
(out of `CH_(3)CHO` and `CH_(3)-underset(O)underset(||)(C)-CH_(3)`)
more the number of hyperconjugating H-atom, more the enol content. Hence enol content in `CH_(3)-underset(O)underset(||)(C)-CH_(3)gt CH_(3)CHO`
`rArr K_(2) gt K_(3) gt K_(1)`
Hence choice (b) is correct while (a), (c) and (d) are incorrect.