The compound CH3 COOCH3 (methyl acetate) is not an acid, but...

The compound $\mathrm{CH}_{3} \mathrm{COOCH}_{3}$ (methyl acetate) is not an acid, but the compound $\mathrm{CH}_{3} \mathrm{COOH}$ (acetic acid is. (a) Which of the hydrogen atoms in acetic acid is the acidic hydrogen (the one that becomes $\mathrm{H}^{+}(a q)$ ion)? (b) Speculate about why none of the hydrogen atoms in methyl acetate is acidic. (Hint: Look carefully at what the acidic hydrogen atom is bonded to in acetic acid.) (c) The diagram below shows how electrons rearrange to make acetic acid behave as an acid. Notice the two different ways the resulting anion is drawn. This allows the negative charge to be spread among two oxygen atoms, which in turn makes the whole anion stable and helps acetic acid to lose an $\mathrm{H}^{+}$ ion and be an acid. What do you call the two different forms of the anion? (Hint: see Section 5.5.)

The compound $\mathrm{CH}_{3} \mathrm{COOCH}_{3}$ (methyl acetate) is not an acid, but the compound $\mathrm{CH}_{3} \mathrm{COOH}$ (acetic acid is.
(a) Which of the hydrogen atoms in acetic acid is the acidic hydrogen (the one that becomes $\mathrm{H}^{+}(a q)$ ion)?
(b) Speculate about why none of the hydrogen atoms in methyl acetate is acidic. (Hint:
Look carefully at what the acidic hydrogen atom is bonded to in acetic acid.)
(c) The diagram below shows how electrons rearrange to make acetic acid behave as an acid. Notice the two different ways the resulting anion is drawn. This allows the negative charge to be spread among two oxygen atoms, which in turn makes the whole anion stable and helps acetic acid to lose an $\mathrm{H}^{+}$ ion and be an acid. What do you call the two different forms of the anion? (Hint: see Section 5.5.)

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Key Concepts

Acidic Hydrogen in Carboxylic Acids

In carboxylic acids, the acidic hydrogen is the one attached to the hydroxyl (–OH) group. This proton is highly acidic because the oxygen, a highly electronegative atom, draws electron density away from the hydrogen, making it easier to lose as H+ in solution.

Resonance Stabilization of Conjugate Bases

Resonance stabilization refers to the delocalization of electrons over multiple atoms, which spreads out and stabilizes charge. When acetic acid loses its acidic hydrogen, the resulting anion (carboxylate ion) is stabilized by resonance as the negative charge is shared between the two oxygen atoms. This stabilization is a key factor in the acid's ability to donate a proton.

Functional Group Structure in Acids vs. Esters

The functional group structures determine the acidic behavior of a compound. In carboxylic acids, the presence of the –OH group attached to a carbonyl (C=O) makes one hydrogen acidic, while in esters, such as methyl acetate, the –OH is replaced by an –OR group, eliminating the presence of a hydrogen that is strongly acidic. As a result, esters do not exhibit acid behavior like carboxylic acids.

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