Unit 19: Carboxylic Acids and Their Derivatives
A carbonyl with a leaving group attached: the same tetrahedral intermediate as a ketone, but one that collapses back down and kicks the leaving group out.
8 topics · 29 questions
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Nomenclature and Acidity of Carboxylic Acids
- How it worksHow does resonance spread the negative charge of a carboxylate over two equivalent oxygens to stabilize the conjugate base?
- Worked exampleFind the correct IUPAC name for CH3CH2CH2COOH.
- Common mistakeWhy isn't a carboxylic acid's acidity mostly explained by the electronegativity of its oxygen atoms alone?
Your turn1 of 2
A carboxylic acid has a pKa of 5. In a solution at pH 7, what percent of the acid exists in its deprotonated, carboxylate form? Use percent ionized = 100 / (1 + 10pka - ph).Relative Reactivity of Acyl Derivatives
- How it worksHow does the leaving group's own stability rank acid chlorides, anhydrides, esters, and amides from most to least reactive?
- Worked exampleFind which is more reactive toward a nucleophile, an ester or an amide, and explain it from leaving group ability.
- Common mistakeWhy doesn't a more reactive acyl derivative also always mean it has a weaker carbon-oxygen double bond?
- Going furtherWhat happens to a synthesis plan when a chemist needs to convert a less reactive amide directly into an acid chloride?
Your turn1 of 2
Which is more reactive toward a nucleophile, an ester or an amide, and why?Nucleophilic Acyl Substitution Mechanism
- How it worksHow does a nucleophile add to the carbonyl to form the same tetrahedral intermediate seen with ketones, but with a leaving group present?
- How it worksHow does that tetrahedral intermediate collapse, re-forming the carbonyl π bond and ejecting the leaving group?
- Worked exampleFind the product when hydroxide attacks the carbonyl of ethyl acetate, working through the tetrahedral intermediate to the carboxylate.
- Common mistakeWhy doesn't nucleophilic acyl substitution look anything like an SN2 reaction, even though both end with a new bond to carbon?
- Ties togetherHow does the tetrahedral-intermediate-plus-collapse pattern from here explain every reaction in the rest of this unit?
Your turn1 of 2
Hydroxide attacks the carbonyl of ethyl acetate. Walk through the tetrahedral intermediate to the final product.Fischer Esterification
- How it worksHow does protonating the carbonyl oxygen make it electrophilic enough for an alcohol to attack under acidic conditions?
- Worked exampleFind the ester product when acetic acid reacts with ethanol under acid catalysis in a Fischer esterification.
- Common mistakeWhy doesn't Fischer esterification go to completion on its own without removing water or using an excess of alcohol?
- Going furtherWhat happens to the reaction when it runs in reverse, with water and acid hydrolyzing an ester back to acid and alcohol?
Your turn1 of 2
Acetic acid reacts with ethanol under acid catalysis in a Fischer esterification. What is the product?Converting Acids to Acid Chlorides
- How it worksHow does thionyl chloride replace a carboxylic acid's hydroxyl with chlorine, generating a great leaving group in the process?
- Worked exampleFind the product when propanoic acid reacts with thionyl chloride, SOCl2.
- Going furtherWhat happens to a synthesis route once an acid becomes its acid chloride: which reactions suddenly become fast and easy?
Your turn1 of 2
Propanoic acid reacts with thionyl chloride, SOCl2. What is the product?Reactions of Acid Chlorides and Anhydrides
- How it worksHow does an acid chloride's excellent leaving group let almost any nucleophile complete a full addition-elimination at room temperature?
- Worked exampleFind the products when acetic anhydride reacts with an excess of ethanol.
- Ties togetherHow does one acid chloride sitting atop the reactivity ladder let a chemist reach nearly every other carboxylic acid derivative?
Your turn1 of 2
Acetic anhydride reacts with an excess of ethanol. What are the products?Amide Formation and Hydrolysis
- How it worksHow does nitrogen's weaker ability to stabilize a negative charge on its own make an amide a worse leaving group than an alkoxide?
- Worked exampleFind the product when an acid chloride reacts with excess ammonia to form an amide.
- Common mistakeWhy doesn't an amide hydrolyze at any appreciable rate at room temperature without strong acid, strong base, or an enzyme?
- Going furtherWhat happens to an amide bond when it sits inside a living cell next to a hydrolytic enzyme instead of on a lab bench?
Your turn1 of 2
An acid chloride reacts with excess ammonia. What is the product?Reduction of Carboxylic Acid Derivatives
- How it worksHow does a hydride add once to kick out the leaving group and form an aldehyde, which a second hydride then reduces further?
- Worked exampleFind the alcohol product when ethyl acetate is treated with excess lithium aluminum hydride followed by an aqueous workup.
- Going furtherWhat happens to an amide instead of an ester when it is reduced with lithium aluminum hydride, forming an amine rather than an alcohol?
Your turn1 of 2
Ethyl acetate is treated with excess lithium aluminum hydride followed by an aqueous workup. What alcohol product(s) form?