THE UNIVERSITY OF ZAMBIA
SCHOOL OF NATURAL SCIENCES
CHE 2505: Organic Chemistry for Medical Students
Tutorial Sheet 4
July 28th 2023
For the week beginning July 31st, 2023
Note: Tutorial mini-tests/quizzes shall be given during the first 15 minutes of each tutorial
session
1. Predict the major organic products of the following reactions. Reaction mechanisms are
not required.
O
(i)
(1)
O
MgBr
Et2O (solvent)
(2) dilute HCl
O
(ii)
(1)
O
MgBr
Et2O (solvent)
(2) dilute HCl
2. Give structures for compounds A-E in the synthetic scheme below.
*Cyclohexanol
K2Cr2O7
acidified
A (C6H10O)
(1) CH3MgBr
+
(2) H3O
E (C7H12O3)
B (C7H14O)
HA
heat
(1) Ag(NH3)2OH
+
(2) H3O
C (C7H12)
(1) O3
(2) Me2S
D (C7H12O2)
3. A compound of formula C5H10O gave a positive reaction with Brady's reagent, gave a
negative reaction with Fehling’s solution and gave a yellow precipitate when treated
with 10% I2/KI and NaOH. Draw the structures of all the compounds that would give
these results.
4. An isomer of the above compound, C5H10O, gave a yellow precipitate with Brady's
reagent, a red precipitate with Fehling’s solution and no reaction with 10% I2/KI and
NaOH. Draw the structures of all the isomers that would react like this.
5. Acids F and G have pKa values of 4.2 and -3.3 respectively.
(i) Which acid is more acidic? Explain.
(ii) Upon reaction with a base, which of these two acids would form a salt with pH
> 7? Explain.
6. Between phosphine (PH3) and ammonia (NH3), which one would you expect to be a
stronger acid? Explain.
7. When the following compounds are mixed, an acid-base reaction is expected. Predict
the products of such a reaction in each case. (pKa (H2O) = 15.7; pKa (PH3) = 27)
(i) PH3 + H2S
(ii) PH3 + H2O
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10. In each of the following organic compounds, two hydrogen atoms are explicitly shown.
Draw the conjugate base corresponding to the deprotonation of each. Hence indicate
which the more acidic hydrogen is.
OH
(i)
Conjugate base 1
Conjugate base 2
Conjugate base 1
Conjugate base 2
Conjugate base 1
Conjugate base 2
Conjugate base 1
Conjugate base 2
OH
(ii) H
O
N
H
(iii) H
(iv)
S
O
H
H
H
N
N
O
O
O
11. Orlistat is an anti-obesity drug which inhibits pancreatic lipase blocking the enzyme
from digesting fats in the intestines. This results in less absorption of fatty acids and
glycerol. Orlistat forms a permanent covalent bond with the enzyme. The first step in
the reaction mechanism involves nucleophilic addition to the carbonyl carbon of the
four-membered ring. The second step forms one of the two intermediates (H or I).
HN
O
HN
O
O
O
O
H
HN
O
O
O
O
O
O
H O
Lipase enzyme
O
O
Lipase enzyme
Intermediate H
O
O
O
H
O Lipase enzyme
HN
O
HN
O
O
Orlistat
O
O
H
O
Lipase enzyme
O
O
O
O
H O
O
Lipase enzyme
Intermediate I
(i) Which of the two intermediates would be favoured?
(ii) Explain your choice in 11(i) fully.
12. Which acid of each pair shown below would you expect to be stronger? Explain.
O
(i)
or
OH
O
(ii)
F
or
OH
O
(iii) F
or
O
F
O
Cl
OH
F
OH
O
OH
O
O
OH
(iv)
OH
or
OH
F3C
2
13. Unknown compound A, (C5H10) rapidly decolourizes a solution of bromine in carbon
tetrachloride. When A is dissolved in cold conc. H2SO4 and when heated with water,
B is formed. B (C5H12O) reacts with chromic acid to give C (C5H10O). both B and C
give positive iodoform tests. Each iodoform reaction mixture contains, in addition to
CHI3, anion of butyric acid, CH3CH2CH2COOH. What is the unknown structures of
A, B, and C?
14. Compound A, (C5H12O) does not give a ppt with phenylhydrazine. Oxidation of (A)
with potassium dichromate gives B, (C5H10O). Compound (B) reacts readily with
phenylhydrazine but does not give tollens test. The original compound (A) can be
dehydrated with conc. H2SO4 to give a hydrocarbon (C), C5H10. Ozonolysis of the
hydrocarbon (C) gives acetone an acetaldehyde. Deduce the structural formulas of
(A), (B) and (C).
15. How would you distinguish between 2-pentanone and 3-pentanone?
16. How would you distinguish between propanone and ethanal?
END OF TUTORIAL QUESTIONS
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