Both alcohols and phenols contain a hydroxyl group, but phenols are more acidic than alcohols. Whereas the acid strength of aliphatic alcohols mainly depends upon the inductive effects, and acid strength of phenols depends upon a combination of both inductive and resonance effects of the substituent and its position on the benzene ring.
Which of the following is the strongest acid?
Answer & explanation
Correct answer: option 1
The correct answer is option 1. \(FCH_2COOH\).
To determine the strongest acid among the given compounds, we need to consider the electron-withdrawing inductive effects of the halogen substituents. The stronger the electron-withdrawing effect, the more the conjugate base is stabilized, resulting in a stronger acid.
1. \(FCH_2COOH\) (Fluoroacetic Acid):
Inductive Effect: Fluorine is the most electronegative halogen, thus it has the strongest electron-withdrawing inductive effect. This significantly stabilizes the conjugate base (fluoroacetate ion).
Acidity: High, due to the strong electron-withdrawing effect of fluorine.
2. \(ClCH_2COOH\) (Chloroacetic Acid):
Inductive Effect: Chlorine is less electronegative than fluorine but still highly electronegative. It provides a strong electron-withdrawing inductive effect, though weaker than that of fluorine.
Acidity: High, but less than fluoroacetic acid.
3. \(BrCH_2COOH\) (Bromoacetic Acid):
Inductive Effect: Bromine is less electronegative than chlorine, resulting in a weaker electron-withdrawing inductive effect.
Acidity: Moderate, less than chloroacetic acid.
4. \(ICH_2COOH\) (Iodoacetic Acid):
Inductive Effect: Iodine is the least electronegative among the halogens listed, resulting in the weakest electron-withdrawing inductive effect.
Acidity: Lowest among the given compounds.
The order of acidity based on the inductive effects of the halogen substituents is:
\(\text{ICH}_2\text{COOH} < \text{BrCH}_2\text{COOH} < \text{ClCH}_2\text{COOH} < \text{FCH}_2\text{COOH}\)
Thus, the strongest acid among the given compounds is \(FCH_2COOH\) (fluoroacetic acid).