A series of substituted benzoic acids is shown below
CHEMISTRY · Multi-part · AP · Chemistry · Acids and Bases · Acids and Bases
Problem
A series of substituted benzoic acids is shown below, where "R" represents the para-substituent on the aromatic ring.
• Compound A: R = OH
• Compound B: R = H
• Compound C: R = OCH3
Answer the following questions about the acidity of these compounds.
(a) For compound A, illustrate two resonance contributors of its conjugate base that place the negative charge on different atoms of the aromatic system.
(b) Predict the order of pKa values for compounds A, B, and C (from smallest pKa to largest pKa).
(c) Justify the order given in part (b) by analyzing the electronic effects of each para-substituent on the stability of the conjugate base.
(d) Propose a new para-substituent that would produce a benzoic acid even stronger than compound A, and explain in detail how that substituent would influence the conjugate-base stability.