clayden2e_problems_ch08

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Problems for Chapter 8 
PROB LEM 1 
How would you separate a mixture of these three compounds? 
N
naphthalene pyridine para-toluic acid
CO2H
 
 
PROB LEM 2 
In the separation of benzoic acid from toluene on p. 164 of the textbook we 
suggested using KOH solution. How concentrated a solution would be 
necessary to ensure that the pH was above the pKa of benzoic acid (4.2)? How 
would you estimate how much KOH solution to use? 
 
PROB LEM 3 
What species would be present in a solution of this hydroxy-acid in (a) water at 
pH 7, (b) aqueous alkali at pH 12, and (c) in concentrated mineral acid? 
CO2H
HO 
 
PROB LEM 4 
What would you expect to be the site of (a) protonation and (b) deprotonation 
if these compounds were treated with the appropriate acid or base? In each 
case suggest a suitable acid or base and give the structure of the products. 
N
H N
H
OH N
N
OH 
 
8 
 
24 Problems to accompany Organic Chemistry 
	
  
PROB LEM 5 
Suggest what species would be formed by each of these combinations of 
reagents. You are advised to use estimated pKa values to help you and to beware 
of those cases where nothing happens. 
O
+
OH
O
HN NH +
O
O
N
H
+
F3C O
O
(a) (b) (c)
 
 
PROB LEM 6 
What is the relationship between these two molecules? Discuss the structure of 
the anion that would be formed by the deprotonation of each compound. 
NN
H
OHO
 
 
PROB LEM 7 
The carbon NMR spectrum of these compounds can be run in D2O under the 
conditions shown. Why are these conditions necessary? What spectrum would 
you expect to observe? 
N
N
H
H2N
O OH
13C NMR 
spectrum 
run in 
DCl/D2O
13C NMR 
spectrum 
run in 
NaOD/D2O
 
 
Problems for Chapter 8 – Acidity, basicity and pKa 25 
	
  
PROB LEM 8 
These phenols have approximate pKa values of 4, 7, 9, 10, and 11. Suggest with 
explanations which pKa value belongs to which phenol. 
OH
NO2O2N
OH
O2N
OH
MeMe
Me
OH OHCl
 
 
PROB LEM 9 
The pKa values of these two amino acids are as follows: 
(a) cysteine: 1.8, 8.3, and 10.8 
(b) arginine: 2.2, 9.0, and 13.2. 
Assign these pKa values to the functional groups in each amino acid and draw 
the most abundant structure that each molecule will have at pH 1, 7, 10, and 
14. 
HS
CO2H
NH2
cysteine
CO2H
NH2
arginine
N
H
H2N
NH
 
 
PROB LEM 1 0 
Neither of these two methods for making pentan-1,4-diol will work. What will 
happen instead? 
H
OH
O
Me MgBr
Me
OH
OH
H
Br OH BrMg OH
Mg
Et2O
MeCHO
 
 
26 Problems to accompany Organic Chemistry 
	
  
PROB LEM 1 1 
Which of these bases would you choose to deprotonate the following 
molecules? Very strong bases are more challenging to handle so you should 
aim to use a base which is just strong enough for the job, but not unnecessarily 
strong. 
H
N
H
OH
O
OH
NH3
Choice of bases:
KOH NaH BuLi NaHCO3