Download 2013 Final Exam File - Fiji National University

College of Engineering,
Science and Technology
School of Sciences
Natabua Campus, PO Box 5529
Lautoka.
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CHM 504: Organic Chemistry
Final Examination, Trimester 2, 2013
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Time allowed: three (3) hours plus 10 minutes reading time
200 marks (50% of final grade)
INSTRUCTIONS
1. There are six (06) questions in this paper, which is seven (07) pages
long, including a table of 1H NMR spectral data..
2. Question 1 is compulsory (80 marks).
3. Answer an additional four questions from questions 2 - 6 (30 marks
each).
4. Write your answers in the answer booklet provided.
5. Start the answer of each question on a new page of your answer
booklet.
6. Write answers of all parts of a question at one place in the answer
booklet.
7. This exam is worth 50% of the overall marks for this unit.
8. You must score at least 80/200 marks (40%) to pass this unit, as well
as 50% overall.
1
Question 1 (compulsory)
(a) Draw the structures of the following molecules, whose IUPAC names are given.
(i) 6-Bromo-2,4-dimethylphenol.
(ii) (E)-5-chlorohept-5-en-2-ol.
[10 marks]
(b) Draw the eclipsed and staggered conformations of 2-methylpropane ( (CH3)3CH ), as
Newman projections, with respect to rotation about any one of the C–C bonds.
[8 marks]
(c) Explain what is meant by each of the following terms.
(i) Meso compound.
(ii) Enantiomers.
[8 marks]
(d) The mass spectrum of an unknown molecule shows a molecular ion peak (M+) at m/z = 72.
Assuming that the compound only contains C, H, and possibly (but not necessarily) O, write
down all reasonable molecular formulae for this compound.
[12 marks]
(e) Each of the molecules shown below has one stereocentre, whose configuration is as shown.
For each molecule, arrange the 4 substituents around the stereocentre in order of priority,
according to the Cahn-Ingold-Prelog Rules, and then assign the stereocentre as R or S.
[12 marks]
(f) Arrange the following carbocations in order of decreasing stability, from left to right.
[6 marks]
(g) What reagents should be used to complete each of the following reactions?
(partial reduction to cis-alkene)
2
(via diazonium salt)
[16 marks]
(h) Shown below is the infra-red spectrum of an unknown compound. Identify the functional
groups present in this molecule.
[8 marks]
Select any four (4) of the remaining five questions.
Question 2
(a) Draw the structures of all isomeric PRIMARY alcohols with the molecular formula C5H12O.
[8 marks]
(b) Explain why phenol (C6H5OH) is more acidic than ethanol (C2H5OH). Clearly draw all
resonance structures that may be relevant to your explanation.
[8 marks]
3
(c) Complete the following reaction by identifying the reactant that gives rise to the product
shown.
[4 marks]
(d) Write down the mechanism of the following reaction, using curved arrows to show the
movement of electron pairs, and clearly drawing the structure of the intermediate F and the
final product G.
[10 marks]
Question 3
Give the major product of each of the following reactions.
(electrophilic addition)
(elimination)
(substitution)
(reduction)
(acetal formation)
(substitution)
[30 marks]
4
Question 4
(a) How many signals would you expect to see in the 13C NMR spectra of each of the following
three isomeric compounds?
[9 marks]
(b) Shown below are the IR and 1H NMR spectra of an unknown compound X, whose
molecular formula is C9H10O. 1H NMR spectral data are provided on the last page.
(i) Calculate the index of hydrogen deficiency of X.
[3 marks]
(ii) Analyse the spectra and deduce the structure of the molecule. Indicate which H atoms in the
molecule give rise to the NMR signals at 1.20 ppm, 2.95 ppm, and 7.4 - 8.1 ppm. Also
indicate what information you can obtain from the IR peak at 1690 cm-1. [Part credit for a
wrong answer cannot be given if you do not indicate how you arrived at that answer.]
[18 marks]
5
Question 5
(a) Give the IUPAC names of the following molecules.
[12 marks]
(b) Triacontyl hexadecanoate, shown below, is a major component of beeswax. It undergoes
hydrolysis when boiled with aqueous NaOH. Give the two products P and Q of this reaction.
[10 marks]
(c) Which compound is the stronger acid, acetic acid (CH3CO2H) or fluoroacetic acid
(FCH2CO2H)? Explain your answer.
[8 marks]
Question 6
(a) List two important functions of complex sugars (polysaccharides) in biological systems.
[8 marks]
(b) Shown on the right is the Fischer projection of the structure of D-galactose.
Draw the structure of its glycoside methyl -D-galactopyranoside as a
Haworth projection.
[6 marks]
(c) Shown below is the structure of the dipeptide derivative aspartame, an
artificial sweetener used in the beverage industry.
(i) There are 5 functional groups in this molecule. Draw the structure of the molecule, circle
each functional group and write the name of the group (e.g., alkene, alcohol, etc.) next to it.
[10 marks]
(ii) Hydrolysis of this molecule with aqueous acid yields, in addition to methanol (CH3OH),
two amino-acids. Draw their structures.
[6 marks]
6
Table 1. 1H NMR Spectral Data (approximate)
 (ppm)
Type of H
0.5 - 1.5
alkyl CH attached to alkyl
1.5 - 2.5
alkyl CH attached to double bond / aromatic ring
2.5 - 3.0
alkynyl CH
2.5 - 4.5
X - CH where X = O, N, Cl, Br
4.5 - 6.5
alkenyl CH
6.5 - 9.0
aromatic CH
9.5 - 10.5
aldehyde CH
1.5 - 6.0
alcohol OH
10 - 12
carboxylic acid CO2H
7