CAIE A-Level Chemistry A2 34.3 Amides Questions

Practise amide formation, hydrolysis, reduction and basicity comparisons using reagents, products and lone-pair delocalisation.

Exam points

identify acyl chloride or anhydride reagents used to form amides from ammonia or amines
predict amide hydrolysis or LiAlH4 reduction products from larger organic structures
explain weak amide basicity by delocalisation of the N lone pair into C=O

Covered syllabus points

34.3.1—Reactions (reagents/conditions)34.3.2—Reactions of amides 34.3.3—Why amides are much weaker bases than amines

[Maximum number: 4]

Amino acids are molecules that contain $-\mathrm{NH}_{2}$ and -COOH functional groups.
Glycine, $\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{COOH}$ , is the simplest stable amino acid.

(a)

Fig. 6.1 shows two syntheses starting with glycine.

Fig. 6.1

[ 2 ]

(i)

Draw the structure of the organic product U that forms when hippuric acid reacts with an excess of $\mathrm{LiAlH}_{4}$ in reaction 3 .

[ 2 ]

Figure for Answer to Question (i) — CAIE A-Level Chemistry A2

- carboxylic acid to primary alcohol COOH to $\mathrm{CH}_{2} \mathrm{OH}$

- amide to amine CONH to $\mathrm{CH}_{2} \mathrm{NH}$

- rest of the molecule is correct (carbons and benzene ring) mark as •

(b)

A student proposes a synthesis of hippuric acid by the reaction of benzamide, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CONH}_{2}$ , and chloroethanoic acid, $\mathrm{ClCH}_{2} \mathrm{COOH}$ .

The reaction does not work well because benzamide is a very weak base.

[ 2 ]

(i)

Explain why amides are weaker bases than amines.

[ 2 ]

M1 nitrogen lone pair in amides is delocalised with C=O

M2 lone pair less available for donation / to accept $\mathrm{H}^{+}$

OR less electron density on N / NH2 so less able to accept H ${ }^{+}$

[Maximum number: 2]

Asparagine and aspartic acid are two naturally occurring amino acids. Their structures and isoelectric points are shown in Table 8.1.

Table 8.1

Asparagine is hydrolysed with an excess of hot NaOH(aq).

Draw the structure of the organic product of this reaction.

M1: hydrolysis of amide to carboxylate ion

M2: hydrolysis of -COOH to carboxylate ion and rest of molecule

$-\mathrm{OOCCH}\left(\mathrm{NH}_{2}\right) \mathrm{CH}_{2} \mathrm{COO}^{-}$

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Covered syllabus points

Question 1

Question (a)

Question (i)

Question (b)

Question (i)

Question 2