School of Science and Sport
Paisley Campus
Session 2014 - 15
Trimester 2
MODULE CODE: CHEM09004
SCQF LEVEL 9
ORGANIC CHEMISTRY 3
Date: 13th May 2015
Time: 1000-1200
Complete all of section A
then choose one question each from sections B, C and D
Page 1 of 7
Exam Ref: CHEM09004 T2 14-15
Section A
Complete all of section A
1
a
Reaction of cis-bromo-4-methylcyclohexane with water gives a mixture of
cis- and trans-4-methylcyclohexanol.
(2)
Give the mechanism of the reaction.
If the products are not obtained in equal amounts, which stereoisomer
will be present in excess?
b
2
The reaction of a primary alkyl chloride with KI is generally carried out in
acetone to maximise the amount of alkyl iodide that is formed. Why
does the solvent increase the yield of alkyl iodide?
(KI is soluble in acetone, but KCl is not)
(2)
Using ethylacetoacetate (I) as an example, account for the increased acidity
of β-ketoesters compared with esters.
(3)
O
O
O
(I)
3
a
b
Draw and name the polymer that results from the polymerisation of this
monomer:
(2)
Draw the structure of the monomer(s) you would use to make the
following polymer :
(2)
4
Imidazole is a five membered aromatic heterocycle.
From your
knowledge of other heterocyclic compounds draw an orbital diagram of
imidazole showing all ‘p’ orbitals and all lone pair orbitals.
Page 2 of 7
(4)
Exam Ref: CHEM09004 T2 14-15
Section B
Choose one question from section B
5
a
Would the acetate ion (CH3CO2─) be a more reactive nucleophile in an
SN2 reaction carried out in methanol or in dimethyl sulphoxide? Explain
your answer.
b
Under which of the following reaction conditions would (R)-2chlorobutane form the most (R)-2-butanol:
i)
ii)
c
(2)
Give the mechanisms and products of substitution reactions of (R)-2bromo-3,4-dimethylpentane under the following reaction conditions:
i)
ii)
d
HO─ in 50% water and 50% ethanol or
HO─ in 100% ethanol?
Explain your answer.
(2)
(5)
with a high concentration of hydroxide
with water in the presence of Ag+
Only one bromoether (ignoring stereoisomers) is obtained from the
reaction of the alkyl dihalide shown with methanol.
(3)
Give the mechanism showing any transition state or intermediate and the
ether product.
e
Give the mechanism and product(s) of the substitution reaction between
(S)-1-bromo-1-fluoroethane and the methoxide ion.
Page 3 of 7
(3)
Exam Ref: CHEM09004 T2 14-15
6
a
Two elimination products are formed from the following E2 reaction:
CH3CH2CHDCH2Br with hydroxide
i) What are the elimination products
ii) Which is formed in the greater yield? Explain
b
(1)
(2)
Three substitution products and three elimination products are obtained
from reaction of 1-bromo-2,2-dimethylcyclohexane with methanol:
Give the mechanisms of the reactions to account for the formation of
these products.
(12)
Page 4 of 7
Exam Ref: CHEM09004 T2 14-15
Section C
Choose one question from section C
7
a
Consider the following reaction:
O
O
NaOEt
CH2(CO2Et)2 +
[A]
EtOH
NaOEt
H
(1 equiv)
O
CO2Et
Give a rational mechanism for the reaction and identify the bracketed
intermediate [A].
b
(6)
Lithium diisopropylamide (LDA) (shown below) is an extremely versatile
base employed in a multitude of valuable carbanion reactions. Explain
why LDA is extremely useful in organic synthesis and justify your answer
with relevant examples.
(5)
N
Li
c
The two molecules below were prepared by Aldol reactions. In each case
indicate the possible starting materials and reagents that would be
required in their synthesis.
O
OH
O
CH
(4)
8
a
Which of the following molecules will be most easily deprotonated to
form a carbanion? Explain your answer.
(3)
(II)
(III)
Question 8 continues overleaf
Page 5 of 7
Exam Ref: CHEM09004 T2 14-15
b
Starting from diethyl malonate (IV) how could you prepare hexanoic acid
(V)?
(4)
(IV)
c
d
(V)
Provide a mechanism for the acid-catalysed decarboxylation step in the
preparation of hexanoic acid from diethylmalonate.
(2)
Compound (VI) below was prepared via the Wittig reaction of a carbonyl
derivative with a phosphorus ylid. Indicate the carbonyl compound
employed and the alkyl halide used to prepare the ylid. Show the
mechanism for the reaction.
(6)
(VI)
Page 6 of 7
Exam Ref: CHEM09004 T2 14-15
Section D
Choose one question from section D
9
a
The polymerisation of styrene proceeds via a free radical mechanism.
(i) What is the purpose of the peroxide reagent?
(ii) Write out a reaction mechanism for the initiation, propagation and
termination steps of this polymerisation.
(iii) Polystyrene is normally “atactic”, what does this mean?
(iv) Polystyrene is thermoplastic, explain why this property is useful for
the exploitation of polystyrene?
b
(6)
(2)
(2)
Below is β-D-glucopyranose drawn in the chair conformation:
(i) Re-draw β-D-glucopyranose in a Haworth projection
(ii) Draw a Haworth projection of -D-glucopyranose
10
(1)
(2)
(2)
Give the mechanisms, showing key intermediates, of reactions of hexan2,5-dione with:
(i) base to form 3-methylcyclopentenone
(ii) acid to form 2,5-dimethylfuran
END OF PAPER
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