Amides (Cambridge (CIE) A Level Chemistry): Flashcards
Exam code: 9701
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- FrontReactions of Amides
What are the two main reactions that the amide group can undergo?
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What are the two main reactions that the amide group can undergo?
The amide group can undergo:
Hydrolysis — by refluxing with aqueous acid or aqueous alkali.
Reduction — using LiAlH4 in dry ether to form an amine.
True or False?
Hydrolysis of a non-substituted amide with aqueous acid produces a carboxylic acid and a primary amine.
False.
Hydrolysis of a non-substituted amide produces a carboxylic acid and ammonia (not a primary amine). Hydrolysis of a substituted amide produces a carboxylic acid and a primary amine.
Define hydrolysis of an amide.
A hydrolysis of an amide is the breakdown of the amide bond by refluxing with aqueous acid or alkali, producing a carboxylic acid plus either ammonia (non-substituted) or a primary amine (substituted).
What is the product of reducing a substituted amide with LiAlH4?
A secondary amine and water. The C=O group is reduced. In a non-substituted amide, reduction gives a primary amine and water.
When a substituted amide is hydrolysed by refluxing with excess acid, the amine produced forms an .......... salt. When hydrolysed with excess base, the carboxylic acid is deprotonated to form a .......... ion.
When a substituted amide is hydrolysed by refluxing with excess acid, the amine produced forms an ammonium salt. When hydrolysed with excess base, the carboxylic acid is deprotonated to form a carboxylate ion.
True or False?
LiAlH4 reduces the C=O group in an amide to form an amine.
True.
LiAlH4 is a strong reducing agent that reduces the carbonyl group (C=O) in the amide. Non-substituted amides give primary amines; substituted amides give secondary amines.
What conditions are required for the hydrolysis of an amide?
The amide is refluxed with either aqueous acid or aqueous alkali. Both conditions break the amide link, but produce different forms of the products.
Amides are formed from the condensation reaction of .......... or acyl chlorides with ammonia or amines. They contain the .......... functional group.
Amides are formed from the condensation reaction of carboxylic acids or acyl chlorides with ammonia or amines. They contain the -CONR2 functional group.
How do the products of alkaline hydrolysis of a substituted amide differ from those of acidic hydrolysis?
In alkaline hydrolysis, the carboxylic acid product is deprotonated to a carboxylate ion, and the primary amine is free. In acidic hydrolysis, the amine is protonated to form an alkylammonium salt, and the carboxylic acid is the free acid.
Why are amides much weaker bases than amines?
The electron-withdrawing oxygen in the amide group removes electron density from the nitrogen atom. This makes the lone pair on nitrogen less readily available for dative covalent bonding, so amides are much weaker bases.
True or False?
Amides are stronger bases than amines because the nitrogen atom in amides still has a lone pair.
False.
Although amide nitrogen does have a lone pair, the electron-withdrawing carbonyl oxygen reduces its availability for dative bonding. Amides are therefore much weaker bases than amines.
Define basicity.
Basicity is the ability of a species to donate its lone pair of electrons to form a dative covalent bond with a proton (H+). It depends on how readily available the lone pair is.
What feature of the amide group reduces the availability of the nitrogen lone pair?
The carbonyl oxygen (C=O) in the amide group is electron-withdrawing. It removes electron density from the nitrogen atom, making the lone pair less available for donation to an electron-deficient species.
Alkyl groups .......... the electron density on nitrogen, making amines more basic. The electron-withdrawing oxygen in amides .......... the availability of the lone pair.
Alkyl groups increase the electron density on nitrogen, making amines more basic. The electron-withdrawing oxygen in amides reduces the availability of the lone pair.
True or False?
Propylamine is a stronger base than phenylamine because alkyl groups donate electron density to nitrogen.
True.
The propyl group has a positive inductive effect, increasing electron density on nitrogen and making the lone pair more available. In phenylamine, the benzene ring withdraws the lone pair through delocalisation, decreasing basicity.
What do amines and amides have in common in terms of their basic properties?
Both contain a nitrogen atom with a lone pair of electrons. However, the basicity of each depends on how available that lone pair is for dative covalent bonding. In amides, the lone pair is much less available due to the electron-withdrawing oxygen.
The order of basicity, from strongest to weakest, is: amine .......... amide. This is because the oxygen in amides .......... electron density from nitrogen.
The order of basicity, from strongest to weakest, is: amine > amide. This is because the oxygen in amides withdraws electron density from nitrogen.
Define electron-withdrawing group.
An electron-withdrawing group is a substituent that removes electron density from adjacent atoms. In amides, the carbonyl oxygen withdraws electron density from nitrogen, reducing the basicity of the compound.
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