Which is the stronger acid in the following pair? Explain your reasoning. Be sure to answer all parts.
p? Methoxyphenol
o? Methoxyphenol
The stronger acidity is due to (select all that apply):
electron-donating inductive effects
intra-molecular hydrogen bonding
electron-withdrawing inductive effects
conjugation with the substituent
Solution
1. Ortho-methoxy phenol is more acidic than para Methoxy phenol.
Since OMe is -I group and it stabilizes the phenoxide ion.
As we know that strength of Inductive effect decreases with the increase of distance. Hence in para isomer, withdrawing effect of OMe is less compared to ortho isomer.
2. Options B, C and D are correct
Intramolecular hydrogen bond: increase the acidity. Ex: ortho Nitro phenol is more acidic than para Nitro phenol, Hydrogen bonding stabilize the anion after proton loosing.
-I groups (NO2, CHO, CN etc) increases the acidity
Conjugation of group also increases the acidity by resonance
Ex: phenol is more acidic than methanol since phenoxide is stabilized by resonance which is not possible to methoxide.
.
Which is the stronger acid in the following pair- Explain your reasoni.docx
1. Which is the stronger acid in the following pair? Explain your reasoning. Be sure to answer all
parts.
p? Methoxyphenol
o? Methoxyphenol
The stronger acidity is due to (select all that apply):
electron-donating inductive effects
intra-molecular hydrogen bonding
electron-withdrawing inductive effects
conjugation with the substituent
p? Methoxyphenol o? Methoxyphenol
Solution
1. Ortho-methoxy phenol is more acidic than para Methoxy phenol.
Since OMe is -I group and it stabilizes the phenoxide ion.
As we know that strength of Inductive effect decreases with the increase of distance. Hence in
para isomer, withdrawing effect of OMe is less compared to ortho isomer.
2. Options B, C and D are correct
Intramolecular hydrogen bond: increase the acidity. Ex: ortho Nitro phenol is more acidic than
para Nitro phenol, Hydrogen bonding stabilize the anion after proton loosing.
-I groups (NO2, CHO, CN etc) increases the acidity
2. Conjugation of group also increases the acidity by resonance
Ex: phenol is more acidic than methanol since phenoxide is stabilized by resonance which is not
possible to methoxide.
