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NAMIBIA UNIVERSITY OF SCIENCE AND TECHNOLOGY
FACULTY OF HEALTH AND APPLIED SCIENCES
DEPARTMENT OF NATURAL AND APPLIED SCIENCES
QUALIFICATION: BACHELOR OF SCIENCE
QUALIFICATION CODE: 07BOSC LEVEL: 6
COURSE CODE: ORC601S COURSE NAME: ORGANIC CHEMISTRY 1
SESSION: JULY 2019 PAPER: THEORY
DURATION: 3 HOURS MARKS: 100
SECOND OPPORTUNITY/SUPPLEMENTARY EXAMINATION QUESTION PAPER
EXAMINER(S) MS. NATALIA SHAKELA
MODERATOR: PROF. HABAUKA KWAAMBWA
INSTRUCTIONS P
ONE Answer ALL the questions.
Write clearly and neatly.
Number the answers clearly
All written work must be done in blue or black ink and sketches can
be done in pencil
5. No books, notes and other additional aids are allowed
PERMISSIBLE MATERIALS
Non-programmable Calculators
ATTACHMENTS
pKa Chart and Periodic Table
THIS QUESTION PAPER CONSISTS OF 15 PAGES
(Including this front page, +H NMR and IR Spectral Data, pKa Chart and Periodic Table)
SECTION A [50]
QUESTION 1: Multiple Choice Questions [50]
e There are 25 multiple choice questions in this section. Each question carries 2 marks.
e Answer ALL questions by selecting the letter of the correct answer.
e Choose the best possible answer for each question, even if you think there is another possible
answer that is not given.
1.1 Consider the following molecule having three labelled protons, Ha, Hb and He. Rank these
protons in order of increasing acidity.
a H.
2C Ha Cc
Hp
A. Ha; Hb; He
B. Hb; He; Ha
C. He; Ha; Hb
D. Hp; Ha; He
1.2 Which of the following choices list the compounds in order of increasing acidity?
A) BrCH,OH <CH3NH2<CH;30H CC) CH;OH <CH;NH)< BrCH,OH B) CH3NH> < CH3OH < BrCH»OH D) CH3;0H<BrCH,OH <CH3NH)
9D
0NW D>
1.3 Which of the following statements is true in comparing ethane, ethene and ethyne to one
another?
A. Ethyne is the weakest acid and has the longest C-H bond distance.
B. Ethyne is the strongest acid and has the shortest C-H bond distance.
C. Ethane is the strongest acid and has the longest C-H bond distance.
D. Ethene is the strongest acid and has the shortest C-H bond distance.
Page 2 of 15
1.4 Which statements about acid-base equilibria are true?
|. The pKa is the negative logio of the acid equilibrium constant
Il. A stronger acid has a pKa with a smaller value than a weaker acid
Ill. A stronger base has a conjugate acid which has a pKa with a smaller value than a weaker
base
IV. The Ka = K [HA]
A. Il, Ill
B. I, Il
C. 1, Il, Il
D. Il, Il, IV
1.5 Which of the following drawings represent the enantiomer of Compound X?
OH oO “ on
« A OH fata OH OH
X A B Cc
A.A
B.B
C..€
D. All of them
1.6 Which of the following properties are not identical for constitutional isomers?
I. Molecular formula ll. Molecular Weight
Ill. Order of attachment of atoms __ IV. Physical Properties
A. |; IV
B. Il; Il
C. |; I
D. II; IV
Page 3 of 15
1.7 Which is the structure of trans-1-ethyl-3-isopropylcyclohexane?
fou H H a) LT b) ph
_—
c) H . q _
$e 8 NL ao~™ A H
A.A
B.B
CC D.D
1.8 How many stereogenic centres are present in the following compound?
O
/~oH
IO
> WN
Fr ©
1.9 How are compounds A and B below related?
H cIR og Clee H ci
72 HY, H Cl H Cl
A B
A and b are enantiomers
A and B are diastereomers
A and B are constitutional isomers
99
» >
A and B are two representations of the same compound
Page 4 of 15
1.10 Which step would most likely have the largest activation energy?
Hg 3 3
+ + H HO Ho” +CP H—Cl
> a step 3. * step 1 step 2
+ cr
A B Cc D
A. Step 1
B. Step 2
C. Step 3
D. It cannot be determined from the information provided
1.11 The IUPAC name of the compound below is:
Cl
2-chloro-4-isopropyl-2,6-dimethyloctane
2,6-dimethyl-2-chloro-4-isopropyloctane
7-chloro-5-isopropyl-3,7-dimethyloctane
09
@ >
2-chloro-4-isopropyl-2,7-dimethyloctane
1.12 What is the IUPAC name for the following compound?
H at \ | C=C H
/ \ f/f CH3 C=C
/ \ H CH2CH3
cis, trans-2, 4-heptadiene
2Z,4Z-2, 4-heptadiene
cis, cis-2, 4-heptadiene
99D >
trans, trans-2, 4-heptadiene
Page 5 of 15
1.13 Using Markovnikov’s rule, predict the position of the Cl atom in the major product from the
reaction of 1-methylcyclohexene with HCl.
A> C
“a
A.A
B.B
C6
D.D
1.14 Which of the following compounds has the highest boiling point?
seen tera A.A
B.B
C.C
D.D
1.15 Which of the following alkenes will react faster with water in the presence of a small
amount of H2SO4?
Ua CO D. A, BandC E. BandC
A.A
B.B
C.C
D.D
Page 6 of 15
1.16 Determine the product of the following reaction:
HzO, HaSO4
== —— ?
HgSO4
O OH
A. ~~, B. A
Oo O
A.A
B.B
C.C
D.D
1.17. Which of the following statements about an SN1 mechanism is true?
. The reaction is fastest with primary halides A
B. The rate of the reaction increases when the solvent is changed from DMSO to Ethanol.
C. The rate of the reaction decreases when the solvent is changed from DMSO to ethanol
D . The identity of the leaving group does not affect the reaction rate.
1.18 Which of the following statements is (are) true about an E2 elimination reaction?
A. It is fastest with 3° Halides
B. It exhibits second-order kinetics
C. A better leaving group should make a faster reaction
D. All of the above are true
1.19 A tertiary halide reacts with a weak base and nucleophile. The reaction will proceed via
which of the following mechanism(s)?
A. Sn
B. Sul and E1
C. E2
D. Sui and E2
Page 7 of 15
1.20 What is the product of the reaction below?
pyridine
1.21
1.22
A.A
B.B
cc
D.D
Which of the following compounds is most likely to show first-order kinetics in a
substitution reaction?
cr S A Br O ~ Br
A B Cc D
Br
A.A
B.B
C.C
D. D
Given the following substitution reaction, what would the effect be of changing the
solvent from CH30H to (CH3)2S=O0?
CH3(CH>)sBr + NaOH ——*> ~ CH3(CH>)S0H + Br
A. The rate would increase because SN2 reactions favour a polar aprotic solvent.
B. The rate would decrease because SN1 reactions favour a polar protic solvent
C. The reaction rate will not be affected
D. The potential change cannot be predicted
Page 8 of 15
1.23 Which of the following anions is the best leaving group?
O oe
CH3CH30~ “OH CH3—C—O
A. B. C.
A.A
B.B
c.C
D. A and B are equal and are the best
1.24 How many peaks could theoretically be observed in the 1H NMR signal(s) for each of the
indicated atoms?
A. A: 7; B: 4; C: 3; D: 3
B. A: 7; B: 3; C: 3; D: 3
C. A: 7; B: 4; C: 2; D: 4
D. A: 7; B: 4; C: 3; D: 4
1.25 Which compound(s) does not give four sets of absorptions in its or their +H NMR spectrum?
Hele E atts HaCHC=CH> H—C—CHCH3 | CH CHg
A B .
A.A B.B C.C D.AandB
Page 9 of 15
SECTION B: [50]
QUESTION 2 [10]
What is (are) the product(s) of the following reactions? Represent the products as skeletal
structures and show the stereochemistry where necessary.
Note: Each question carries 2 marks.
Substitution only a) “Br + CH30OH TT
b) Br - Me —_>
Br -
NH> 7
Br (2 equivalents)
1} BH3 Te
do NANI 2) H2Os/OH"
Ho ep \ __
— SSS aaa
Lindlar's catalyst
Page 10 of 15
QUESTION 3 [10]
Determine the reagents required to achieve each of the following transformations.
Note: Each question carries 2 marks.
a) Jor — Joe
cao b) NS
WTO -2 ' + .O yes son Br OH
? O
2 SJ a see
? ZB ys,
e) PO ~_FA
QUESTION 4 [10]
Draw a stepwise, detailed mechanism for the reaction BELOW. In order to receive full marks,
show all the electron movement, the intermediates and all the products formed.
Jf a
SN water encode ?
Page 11 of 15
QUESTION 5 [10]
Draw a stepwise, detailed mechanism for the following reaction. In order to receive full
marks, show all the electron movement; draw all the intermediates and all the products.
Hint: The reaction produces two alkene products
Ux. CHg C “fo “OH —_—\_—_»>
QUESTION 6 [10]
An unknown compound A has the molecular formula Ci2Hi60. A absorbs strongly in the IR at
1715 cm}. The +H NMR spectral data for A are given below. What is the structure of A?
absorption ppm ratio of absorbing H’s singlet 1.0 6 triplet 1.2 3 quartet 22 2
broad singlet 7.0 5
END OF EXAMINATION QUESTIONS
GOOD LUCK!
Page 12 of 15
1H NMR SPECTRAL DATA
Characteristic Chemical Shifts of Common Types of Protons
Type of proton Chemical shift (ppm) Type of proton Chemical shift (ppm)
\ te 5S. Pa 4.5-6 . ra
a | sp*
° RCH, ~0.9 © RoCHes ~1.3 Cp 6.5-8 ° RCH ~1.7
ar 6-2.5 r r ote oa 9-10 R7 ~H
Z=C,O,N
e —C=C-+H ~2.5 om 10-12
R~ “OH
—hiy 2.5-4 31 RO-H or RON-H 15
sp- Zz |
Z=N,0,X
Important IR Absorptions
Bond type Approximate ¥ (cm) intensity
O-H 3600-3200 strong, broad
N-H 3500-3200 medium
C-H ~3000
e C.2-H 3000-2850 strong
© C.2-H 3150-3000 medium
© Cs-H 3300 medium
C=G 2250 medium
C=N 2250 medium
C=0 1800-1650 (often ~1700)} strong
C=C 1656 medium
Ss
i A 1600, 1500 medium
Page 13 of 15
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