NAME:_______________________
Chemistry Olympiad, Ontario Division
March Examination 2009
Note: The Preparatory Problems published by the UK hosts of the 2009
International Chemistry Olympiad contain topics concerning different aspects
of inorganic, physical, analytical and organic chemistry. There is no particular
emphasis on one sub-discipline of chemistry, hence this examination reflects
that fact. It is understood that some of the organic chemistry topics are not
covered by the curriculum of Canadian Secondary schools. You are urged to
consult any current textbook on organic chemistry for help.
Instructions:
1.
Write your name at the top of this page and each of the following
pages.
2.
Using the spaces provided for answers, attempt all questions and
show all necessary working.
3.
Solutions should be mailed to the address below on or before
April 17th 2009 (they should be received on or before Friday April 24th
2009 for credit).
4.
Please DO NOT send anything other than this examination paper.
Anything else submitted will not be marked.
5.
Please DO NOT send your solutions by email! They must be sent by
regular Canada Post delivery to the following address:
Dr. David C. Stone
Department of Chemistry
University of Toronto
80 St. George Street
TORONTO, Ontario
M5S 3H6
1. (i). Thiamphenicol (formula C12H15Cl2NO5S, structure below) is an
antibacterial agent used in many countries as a veterinary antibiotic.
5
H3C
S
O O
OH
Cl
4
1 Cl
H
3 N 2
thiamphenicol
O
OH
(a).Calculate the percentage of nitrogen present in thiamphenicol.
(b). Name the functional groups present in thiamphenicol.
(c). What is the hybridization of the numbered carbon atoms and the nitrogen
atom in the thiamphenicol structure shown above?
(d). Which (if any) of the numbered carbon atoms in thiamphenicol are
stereocenters (chiral centers)? How many stereoisomers of thiamphenicol are there?
(ii). As an essential amino acid, threonine ((2S, 3R)-2-amino-3-hydroxybutanoic
acid) is not synthesized in humans and must be ingested in the form of
threonine-containing proteins. Draw the Fischer projections of all stereoisomers of
threonine, using the template given below.
COOH
CH3
2. Rohypnol is the trade name for the compound flunitrazepam whose structure
is shown in the scheme below. It is a controversial sedative which has been
misused to 'spike' people's drinks.
(a). Draw the structures for the reagent phenylhydrazine and compounds A to L.
A=
B=
C=
D=
E=
F=
G=
H=
I=
J=
K=
L=
Phenylhydrazine =
3. A voltaic cell is constructed as follows:
Ag (s)|Ag+ (0.015 M)||Fe3+ (0.055 M), Fe2+ (0.045 M)|Pt (s)
(a).
Calculate the initial value of Ecell.
(b).
As the cell operates, will Ecell increase, decrease, or remain constant? Explain
(in less than 10 words).
(c).
Calculate the Ecell when [Ag+] has increased to 0.02M.
(d).
What will be the [Ag+] when Ecell = 0.01V?
(e).
What are the ion concentrations when Ecell = 0?
4. The phosphorus isotope 32P is used in biochemical studies to determine pathways
of phosphorus atoms in living organisms. Its presence is detected through radioactive
emission of β- particles.
(a). What is the radioactive decay constant for 32P, expressed in units of s-1?
(b). What is the activity of a 1.00 mg sample of 32P?
(c). Approximately what mass of 32P will remain in the original 1.00 mg sample after
57 days?
(d). What will be the rate of radioactive decay after 57 days?
5. (i). Draw the likely structures of the following chelate complexes, showing any
geometric isomers:
(a) [Cr(ox)3]3(b) [CrCl2(en)2]+
(en = 1,2-ethylenediamine; ox = oxalate)
(ii). The color of [Cr(H2O)6]Cl3 is violet, whereas the color of [Cr(NH3)6]Cl3 is
yellow. Explain the difference in color, with the use of a diagram.
6. Peroxyacetyl nitrate (PAN) is an air pollutant produced in photochemical smog
by the reaction of hydrocarbons, oxides of nitrogen, and sunlight. PAN is unstable
and dissociates into peroxyacetyl radicals and NO2 (g). Its presence in polluted air
is like a reservoir for NO2 storage.
O
H3C C OONO2
O
H3C C OO + NO2
The first order decomposition of PAN has a half life of 35 hours at 0°C and
30 minutes at 25°C. Calculate the temperature at which a sample of air containing
5.0 x 1014 PAN molecules per liter decomposes at the rate of 1.0 x 1012 PAN
molecules per liter per minute.
7. Maleic acid is an organic compound used in dyeing and finishing fabrics and as
a preservative of oils and fats. It contains only the elements C, H and O.
(a). In a combustion analysis, a 1.054 gram sample of maleic acid yielded 1.599 g
of CO2 and 0.327 g of H2O. In a freezing point depression experiment, a 0.615 g
sample of maleic acid dissolved in 25.10 g of glacial acetic acid, (CH3COOH,
which has the freezing point depression constant Kf = 3.90 °C m-1), lowers the
freezing point by 0.82°C. Determine the empirical and molecular formulae of
maleic acid. (All calculations must be shown for full credit).
(b). In a titration experiment, a 0.425 g sample of maleic acid is dissolved in
water and requires 34.03 mL of 0.2152 M KOH for its complete neutralization.
Use the results in part (a) and the titration data to rewrite the molecular formula to
show the number of ionizable H atoms in the molecule.
(c). The pH of a 0.215 g sample of maleic acid dissolved in 50 mL of aqueous
solution is found to be 1.80. Determine the first ionization constant of maleic acid.
(d). Calculate the expected pH of a 0.05 M aqueous solution of maleic acid.
Assume all the [H3O+] arises from the first ionization.
8. (i). What fragments would you expect in the mass spectra of the following
compounds? Show the structures of the fragments and the m/z values for each.
O
OH
CH3
N
H
(ii). Compound A (formula C10H16) has IR absorbances at 1640 cm-1 and 3000-3100
cm-1. Compound A undergoes ozonolysis under reducing conditions to form two
fragments, B and C with formulae of C6H8O3 and C4H8O, respectively. Compound B
reacts with Tollens’ reagent (Ag2O, NH3) to form a silver mirror in a reaction test
tube, and compound C gives a positive iodoform test. Compound A does not react
with Tollens’ reagent and does not give a positive iodoform test. Using the NMR data
given below for compounds B and C and the data above, draw structures for
compounds A, B and C.
NMR data for compound B: δ = 1.95 ppm (quintet, 2H)
δ = 2.4 ppm (multiplet, 4H)
δ = 9.6 ppm (singlet, 1H)
δ = 9.72 ppm (triplet, 1H)
NMR data for compound C:
δ = 1.06 ppm (triplet, 3H)
δ = 2.09 ppm (singlet, 3H)
δ = 2.49 ppm (quartet, 2H)
(NMR peak format: singlet, triplet, quartet, multiplet refer to splitting of each signal
and the number of H atoms refers to the integration of each peak in the spectra).
Compound A:
Compound B:
Compound C:
9. (i). Propose necessary organic and inorganic reagents for the following
transformations:
O
O
O
O
OCH2CH3
O
OCH2CH3
O
(ii). Lithocholic acid is a steroid found in human bile. Predict the product of reaction
of lithocholic acid with each of the following reagents:
CrO3, H+
BH3, H+
COOH
CH3
Tollens' reagent
CH3 H
HO
H
H
H
(CH3)3SiCl, Et3N
H
H
Lithocholic acid
CH3MgBr, H+
LiAlH4, H+
10. Provide a structural formula for each of the two compounds (X and Y) given
below using the spectral data provided.
(a). X: C8H6O2
IR:
X: 1H NMR:
X: 13C NMR:
solvent
Structure X:
(b). Y: C9H16O5
IR:
Y: 1H NMR:
solvent
Y: 13C NMR:
solvent
Structure Y:
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