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Questions and Answers
Which of the following is a carboxylic acid derivative in which the hydroxy group (—OH) is replaced by an alkoxy (—OR)?
Nitriles contain the cyano group.
True
What do nitriles contain?
cyano group
Most acid derivatives have C=O stretches between __ cm–1 and __ cm–1.
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What is the most generalized method for making anhydrides?
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Using a cyclic anhydride allows for both acid groups to react simultaneously.
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What type of rings favor the formation of lactones?
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Strong dehydrating agents like ____ can eliminate the elements of water from a primary amide to give a nitrile.
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Match the following types of lactams with their corresponding amino acids:
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Study Notes
Carboxylic Acid Derivatives
- Defined as compounds with functional groups that can be converted to carboxylic acids by a simple acidic or basic hydrolysis
Esters
- Carboxylic acid derivatives with a hydroxy group (—OH) replaced by an alkoxy (—OR) group
- Cyclic esters are called lactones
Amides
- Composite of a carboxylic acid and ammonia or an amine
- Ammonium salts are converted to amides at high temperatures with loss of H2O
- Cyclic amides are called lactams
Nitriles
- Contain the cyano group (—CN)
- Electronic structure of nitriles: the atoms at the ends of the triple bonds are sp hybridized, and the bond angle is 180°
Acid Halides
- Also called acyl halides
- "Activated" derivatives (highly electrophilic) used in the synthesis of other acyl compounds such as esters
Acid Anhydrides
- Contain two molecules of acid, with loss of a molecule of water
- "Activated" derivatives of carboxylic acids (highly electrophilic)
Spectroscopy of Carboxylic Acid Derivatives
- IR spectroscopy: most acid derivatives have C=O stretches between 1700 cm–1 and 1800 cm–1
- 1H NMR spectroscopy: proton chemical shifts are close to those of similar protons in ketones, aldehydes, alcohols, and amines
- 13C NMR spectroscopy: useful for determining the structure of acid derivatives
Nucleophilic Acyl Substitution
- Interconversion of acid derivatives occurs by nucleophilic acyl substitution
- Proceeds via an addition–elimination mechanism
- More reactive derivatives can be converted to less reactive derivatives
Reactivity of Carboxylic Acid Derivatives
- Acid chlorides are the most reactive, followed by anhydrides, esters, and amides
- Nitriles are the least reactive
Interconversion of Carboxylic Acid Derivatives
- Acid chlorides can be converted to anhydrides, esters, and amides
- Anhydrides can be converted to esters and amides
- Esters can be converted to amides
- Amides can be converted to esters and acid chlorides
Leaving Groups in Nucleophilic Acyl Substitutions
- A strong base, such as an alkoxide (–OR), is not usually a leaving group, except in an exothermic step
- In the nucleophilic acyl substitution of esters, the elimination of the alkoxide is highly exothermic, converting the tetrahedral intermediate into a stable molecule
Transesterification
- One alkoxy group can be replaced by another with acid or base catalyst
- Use a large excess of the desired alcohol to displace the equilibrium
Hydrolysis of Acid Derivatives
- Acid chlorides and anhydrides are hydrolyzed quickly, even in moist air with no acid or base catalyst
- Esters are hydrolyzed to carboxylic acids under basic conditions (saponification)
- Amides are hydrolyzed to carboxylic acids under acidic or basic conditions
- Nitriles are hydrolyzed to carboxylic acids under acidic or basic conditions
Reduction of Acid Derivatives
- Lithium aluminum hydride (LiAlH4) reduces esters, acids, and acyl chlorides to primary alcohols
- Lithium tri-tert-butoxyaluminum hydride is a milder reducing agent that reacts faster with acyl chlorides than with aldehydes
- Di-isobutylaluminum hydride (DIBAL-H) is a mild reducing agent that reduces esters to aldehydes at -78 °C
- Amides can be reduced to amines using LiAlH4
Organometallic Reagents
- Grignard and organolithium reagents add twice to acid chlorides and esters to give alcohols after protonation
- Dialkylcuprate reagents (Gilman reagents) react with acid chlorides to give ketones
Synthesis of Acid Derivatives
- Acid chlorides can be synthesized using thionyl chloride (SOCl2), oxalyl chloride (COCl)2, and phosgene (COCl2)
- Anhydrides can be synthesized by reacting an acid chloride with a carboxylic acid or a carboxylate salt
- Esters can be synthesized by reacting an acid chloride with an alcohol
- Amides can be synthesized by reacting an acid chloride with ammonia or an amine
- Nitriles can be synthesized by reacting an acid chloride with a cyanide ion
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Description
Test your knowledge of carboxylic acid derivatives, nitriles, and anhydrides in organic chemistry. Learn about the characteristics and reactions of these compounds.
