Question

The correct order of increasing pKa values of the compounds:
(A) CH$_3$COOH
(B) CH$_2$OCH$_2$COOH
(C) Cl$_3$COOH
(D) (CH$_3$)$_3$CCOOH
Choose the correct answer from the options given below:

• A. A $<$ B $<$ C $<$ D
• B. A $<$ C $<$ B $<$ D
• C. B $<$ A $<$ C $<$ D
• D. C $<$ B $<$ A $<$ D

Answer 1

The Correct Option is A

The order of increasing pKa values corresponds to increasing acidity. A lower pKa signifies a stronger acid. Analysis of each compound follows:

1. CH₃COOH (Acetic acid): A typical weak carboxylic acid.
2. CH₂OCH₂COOH (Glycolic acid): An ether group's electron donation can slightly diminish acidity.
3. Cl₃COOH (Trichloroacetic acid): Electron-withdrawing chlorine atoms enhance acidity by stabilizing the conjugate base.
4. (CH₃)₃CCOOH (Trimethylacetic acid): The sterically bulky, electron-donating tert-butyl group reduces acidity relative to simpler carboxylic acids.

Consequently, the order from lowest to highest pKa (representing increasing acidity) is: CH₃COOH < CH₂OCH₂COOH < Cl₃COOH < (CH₃)₃CCOOH.

Therefore, the correct sequence is A < B < C < D.