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

Andrew Burrows, John Holman, Andrew Parsons

Chapter 19

Organic reaction mechanisms - all with Video Answers

Educators

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Chapter Questions

Problem 1

Use the symbols $+I,-I,+M,-M$ to identify the inductive and mesomeric effects of the following groups: (a) - Et; (b) - CHO; (c) $-\mathrm{NO}_{2} ;(\mathrm{d})-\mathrm{NH}_{2} ;(\mathrm{e})-\mathrm{OCH}_{3} ;$ (f) $-\mathrm{CO}_{2} \mathrm{CH}_{3}$. (Section $\left.19.1\right)$

RS

Rajesh S.

Numerade Educator

Problem 2

Suggest a reason why the methyl cation and primary carbocations without resonance should never be proposed in a reaction mechanism unless no other pathway is possible.
(Section 19.1)

Nicholas S.

Numerade Educator

Problem 3

Explain why the allyl radical $\left(\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}-\mathrm{CH}_{2}\right)$ is more stable than a tert-butyl radical $\left(\mathrm{Me}_{3} \mathrm{C}^{\circ}\right)$. (Section 19.1)

Nicholas S.

Numerade Educator

Problem 4

Rank the following carbanions (A-C) in order of increasing stability. Explain your reasoning. (Section 19.1)

Nicholas S.

Numerade Educator

Problem 5

The following questions relate to quinine, a naturally occurring antimalarial agent. (Sections $19.1$ and 19.2)
(a) (i) Identify, giving your reasons, the most acidic hydrogen atom in quinine.
(i) Draw the product from the reaction of quinine with sodium hydride $\left(\mathrm{Na}^{+} \mathrm{H}\right)$ ) and give a mechanism (using curly arrows) to show its formation.

RS

Rajesh S.

Numerade Educator

Problem 6

The following questions relate to the sequence of reactions shown below. (Sections $19.2$ and 19.3)
(a) What type of polar reaction is taking place in step 1 ?
(b) What type of polar reaction is taking place in step 2 ?
(c) Explain why the reaction in step 2 is a regioselective reaction.
(d) Explain why the reaction in step 2 is a stereoselective reaction.

RS

Rajesh S.

Numerade Educator

Problem 7

(S)-(t)-Clopidogrel bisulfate (Plavix) is an orally active medicine that helps to prevent harmful blood clots and it is used as an antithrombotic agent. It is prepared by treating the S isomer of clopidogrel with sulfuric acid in an acid-base reaction. A racemic synthesis of clopidogrel is shown below. (Sections $19.2$ and $19.3$ )
(a) In step 1, assign oxidation levels to the two carbon atoms identified by the purple asterisk ("). Use these values to determine if the transformation in step 1 involves oxidation, reduction, or neither.
(b) What type of polar reaction is taking place in step 2 ?
(c) In step 3, assign oxidation levels to the two carbon atoms identified by the dark red asterisk ("). Use these values to determine if the transformation in step 3 involves oxidation, reduction, or neither.
(d) What type of polar reaction is taking place in step 4 ?
(e) Decide which of the terms chemoselective, regioselective, and stereoselective apply, to step 4 .
(f) What type of polar reaction is taking place in step $5 ?$
(g) What type of polar reaction is taking place in step 6 ?
(h) Giving your reasons, draw the $\mathrm{S}$ isomer of clopidogrel (Hint: See Section 18.4, p. 845 ).
(i) Draw the structure of (S)-(t)-clopidogrel bisulfate (Plavix).

RS

Rajesh S.

Numerade Educator