Explaining Acidities of Ortho, Meta, & Para Fluorophenols

  • Thread starter Thread starter sciontc03
  • Start date Start date
  • Tags Tags
    Phenol
Click For Summary
SUMMARY

The acidity differences among ortho, meta, and para-fluorophenols are primarily influenced by the inductive effect of the fluorine atom rather than resonance stabilization. The pKa values demonstrate this, with ortho-fluorophenol at 8.81, meta-fluorophenol at 9.28, and para-fluorophenol at 9.81, compared to phenol's pKa of 10.0. Although ortho and para positions have four resonance structures, the meta position has only three, leading to a misconception about stability. The inductive effect of fluorine, acting as an electron-withdrawing group, significantly impacts acidity more than resonance contributions.

PREREQUISITES
  • Understanding of acidity and pKa values
  • Knowledge of resonance structures in organic chemistry
  • Familiarity with electron-withdrawing and electron-donating groups
  • Basic concepts of inductive effects in chemical reactions
NEXT STEPS
  • Study the role of electron-withdrawing groups in acidity
  • Explore resonance vs. inductive effects in organic compounds
  • Investigate the pKa values of other substituted phenols
  • Learn about the stability of carbanions and their relation to acidity
USEFUL FOR

Chemistry students, organic chemists, and anyone interested in understanding the factors influencing acidity in aromatic compounds.

sciontc03
Messages
9
Reaction score
0

Homework Statement


How do you explain the difference in acidity of the ortho, meta, and para- fluorophenols.


Homework Equations





The Attempt at a Solution



I know that EWG enhance the acidity of phenols because they stabilize the delocalized negative charge.
I also drew out the resonance structures and saw that ortho and para positions have 4 resonance structures, whereas meta has only 3 structures. This means ortho and para would be more stable. However, the pKa show different.
pKa of phenol = 10.0
pKa of ortho-fluorophenol = 8.81
pKa of meta-fluorophenol = 9.28
pKa of para-fluorophenol = 9.81

How do you explain this?
 
Physics news on Phys.org
If the fluorine were affecting the acidity via resonance, fluorine would act as an electron donating group, rather than an electron withdrawing group. The inductive effect is more important here than the resonance effects because resonance structures where the fluorine has a + charge are very small contributors.
 

Similar threads

Why Is Para Nitro Phenol More Acidic Than Ortho Nitro Phenol?
  • · Replies 5 ·
Replies
5
Views
3K
Electrophilic Aromatic Substitution
  • · Replies 2 ·
Replies
2
Views
2K
Organic Chemistry: acid pKa of a substituted phthalic acid
  • · Replies 12 ·
Replies
12
Views
19K
Aromatic substitution and it's effect on proton NMR?
  • · Replies 2 ·
Replies
2
Views
9K
Comparing acidity among 3 compounds - pic included
  • · Replies 1 ·
Replies
1
Views
5K
Organic Chemistry Q&A: Activating and Deactivating Groups
  • · Replies 11 ·
Replies
11
Views
11K