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Chemistry: 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

Educators

Chapter Questions

12:08

Problem 1

The following questions are based on the reactions of ethyl ethanoate $(1) \text { shown below. (Sections } 24.2 \text { and } 24.3)$
(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 $^{16}$ 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 $12.1, \text { p.558 })$
(i) Draw a reaction mechanism to show how 1 is converted into 4 and $\mathrm{EtOH}$.
(ii) If 1 is heated with $\mathrm{H}_{2}^{18} \mathrm{O}$ and $\mathrm{H}^{+}$, where does the $^{18} \mathrm{O}$ atom appear at the end of the reaction?
(iii) If ethyl ethanoate, labelled with $^{18} \mathrm{O}$ 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

Nicholas Sacco
Nicholas Sacco
Numerade Educator
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 Sacco
Nicholas Sacco
Numerade Educator
05:02

Problem 3

Part of a synthesis of the oral contraceptive norgestimate is shown below. (Section 24.2 )
(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 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 $\mathrm{NH}_{2} \mathrm{OH}, \mathrm{H}^{+} ?$
(i) Suggest a mechanism to explain the formation of compound 10
(ii) Draw two different enol forms of compound 10

Nicholas Sacco
Nicholas Sacco
Numerade Educator
02:37

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, $\operatorname{se} \theta$ 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 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.

Crystal Wang
Crystal Wang
Numerade Educator
00:54

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 )
(a) Why is the formation of nylon- 6,6 called a condensation polymerization?
(b) Why does the formation 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 hexanedioy 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 A and B.
(ii) Under what conditions would you expect path $\mathrm{B}$ to be favoured over path $A ?$

Catherine Lemar
Catherine Lemar
Numerade Educator
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 Sacco
Nicholas Sacco
Numerade Educator