James M. answered • 01/12/24
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1 < 2 < 3
1 is a non-aromatized enol (tautomer of cyclohexanone) and is thus the least acidic (highest pKa). This is because the resulting anion (the conjugate base) is delocalized but not by very much.
2 (phenol) is an aromatic (unusually stable) enol and is more acidic as the charge is delocalized over a greater number of atoms
3 (4-hydroxyacetophenone) is like 2 (an aromatic enol) however it contains an electron-withdrawing group at the para (or 4-) position. Both resonance and inductive effects reduce the instability of the conjugate base.
Acidity and stability are similar and move in the same direction. There is a difference between Kinetic stability and thermodynamic stability in acids, however, which type of stability is meant is unclear. One can say unambiguously that the stronger the acid is, the less stable it is, and the more readily it ionizes.
James M.
the substituent in 3 is an acyl group. Such groups are electron- withdrawing by resonance (M-). You will learn that this group is a deactivating "meta director" in Organic II.01/12/24
0825 2.
Can O show +M effect in 3?01/12/24