Chemistry $^{3}$ : Introducing inorganic, organic and physical chemistry

Andrew Burrows, John Holman, Andrew Parsons

Chapter 24 Carboxylic acids and derivatives: nucleophilic acyl substitution and $\alpha$-substitution reactions - all with Video Answers

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Chapter Questions

Problem 1

The following questions are based on the reactions of ethyl ethanoate (1) shown below. (Sections $24.2$ and 24.3)
(a) Give appropriate reagents for converting 1 into 2 . Is this an example of an oxidation or a reduction reaction?
(b) Give the structure of organic compound 3 .
(c) Oxygen-18 labelling is often used to establish the mechanism of a reaction. A ${ }^{16} \mathrm{O}$ oxygen in a starting material is replaced by an ${ }^{18} \mathrm{O}$ atom and the position of the ${ }^{18} \mathrm{O}$ atom at the end of the reaction recorded using mass spectrometry (Section 12.1, p.558).
(i) Draw a reaction mechanism to show how 1 is converted into 4 and EtOH. (ii) If 1 is heated with $\mathrm{H}_{2}{ }^{\mathrm{T} \theta} \mathrm{O}$ and $\mathrm{H}^{+}$, where does the ${ }^{18} \mathrm{O}$ atom appear at the end of the reaction?
(iii) If ethyl ethanoate, labelled with ${ }^{19} \mathrm{O}$ as shown below, is heated with $\mathrm{H}_{2} \mathrm{O} / \mathrm{H}^{+}$, where does the ${ }^{18} \mathrm{O}$ atom appear at the end of the reaction? (d) Draw a reaction mechanism to show how 1 is converted into 5 .
(e) Draw the major enol form of compound 5 .

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11:38

Problem 2

(a) The following questions relate to the formation of lactone 7 from keto-ester 6. (Sections $24.2$ and $24.3$ )

Nicholas S.

Numerade Educator

Problem 3

Part of a synthesis of the oral contraceptive norgestimate is shown below. (Section 24.2) (i) Suggest a mechanism to explain the formation of 7 .
(a) To what class of compound does norgestimate belong $-$ is it a peptide, a fatty acid, a steroid, or a carbohydrate?
(b) Propose a mechanism to explain the conversion of alcohol 11 into ester 12 .
(c) Give the structure of a reagent, other than ethanoic anhydride, that will convert 11 into 12
(d) Explain why $\mathrm{NaOH}$ reacts with only one of the ester groups in compound $12 .$ (Hint. Consider the relative electrophilicity of the carbonyl carbons.)
(e) What functional group is formed when compound 13 reacts with $\mathrm{NH}_{2} \mathrm{OH}, \mathrm{H}^{+}$?
(ii) Explain why the reaction of 6 with $\mathrm{NaBH}_{4}$ is chemoselective.
(iii) Give the structure of the organic product from reaction of 6 with $\mathrm{LiAlH}_{4}$ then $\mathrm{H}^{+}$.
(b) The following questions relate to the formation of compound 10. (Sections $24.2$ and $24.3$ )
(i) Suggest a mechanism to explain the formation of compound $10 .$
(ii) Draw two different enol forms of compound $10 .$

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Problem 4

In nature, aromatic compounds are formed by the cyclization of polyketide chains (containing alternating $\mathrm{C}=\mathrm{O}$ and $\mathrm{CH}_{2}$ groups, see p.1130) in the presence of enzymes. The polyketide chains have a thioester group (RCOSR) at the end of the chain, which, like esters, reacts in Claisen-type reactions. For example, thioester 14 is converted into phloracetophenone. Phloracetophenone, obtained from the

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Problem 5

Nylon- 6,6 is a synthetic polyamide. It is formed by heating, hexane-1,6-diamine with hexanedioic acid (adipic acid) in a condensation polymerization reaction. (Section 24.2) plant Curcuma comosa, has been shown to lower cholesterol levels in animals. (Section $24.3$ )
(a) Propose a mechanism that explains how compound 15 is converted into phloracetophenone.
(b) For phloracetophenone, explain why the position of the equilibrium lies heavily to the right. (a) Why is the formation of nylon- 6,6 called a condensation polymerization?
(b) Why does the fomation of nylon- 6,6 from hexane-1, 6-diamine and hexanedioic acid require heating?
(c) If hexanedioic acid is replaced by hexanedioyl dichloride, then reaction with hexane- 1,6 -diamine forms nylon- 6,6 at room temperature. Why does the polymerization using hexanedioyl dichloride take place under milder reaction conditions?
(d) Nylon- 6,6 is recycled by hydrolysing all of the amide bonds to reform the monomers, and then repolymerizing. Hydrolysis of amide bonds under basic conditions requires heating in a concentrated aqueous solution of hydroxide ions. As shown below, two reaction pathways are possible.
(i) Use curly arrows to show the movement of electrons in paths $\mathrm{A}$ and $\mathrm{B}$.
(ii) Under what conditions would you expect path $\mathrm{B}$ to be favoured over path A?

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05:20

Problem 6

Part of a synthesis of a naturally occurring steroid called equilenin is shown below. (Section 24.3) (a) Propose a mechanism that explains how compound 16 is converted into compound $17 .$
(b) Propose a mechanism that explains how compound 18 is converted into compound 19 .

Nicholas S.

Numerade Educator