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Chemistry 2440
Fall (Loader) Version 1
Test # 2
[50 Marks Total]
Name: _____________________
October, 22nd 2004
MUN #: ______________________
50 minutes
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Marks
QUESTIONS
VALUE
1
18
2
16
3
16
Total
50
-1-
MARKS
CHEMISTRY 2440
[MARKS]
1.
(a)
Give the correct IUPAC name for each of the following compounds.
CH3
(i)
CH
H2C
C
CH3
O
CH
H2C
3,6-dimethyloctan-4-one
CH3
CH3
CH3
O
(ii)
CH2
H
H3C
2-methyl-4-oxopentanal
O
[10]
(iii)
(CH3CH2)2CHCH2CH(CH3)COOCH2CH2CH3
propyl 4-ethyl-2-methylhexanoate
O
(iv)
Cl
3-chlorobenzaldehyde
C
H
O
(v)
OH
HO
O
4-methylheptanedioic acid
CH3
(b)
The compound 4-hydroxypentanal can form a hemiacetal. Draw the
structure for 4-hydroxypentanal and the intramolecular hemiacetal.
H
H3C
O
OH
4-hydroxypentanal
H3C
H
O
OH
5-methyltetrahydrofuran-2-ol
[3]
[5]
(c)
Explain how you could use a chemical test to distinguish between
two test tubes, one containing aqueous propanone, and the other
propanal. (Make sure that you show how the test works and give
chemical reactions as needed).
Propanone (acetone) is CH3COCH3 and propanal is CH3CH2CHO. The aldehyde can be easily
oxidized further to the caboxylic acid while propanone is not easily oxidized. The Tollens’ Test
for aldehydes makes use of this difference in properties. (Tollens’ reagent is made by adding
sodium hydroxide to silver nitrate solution to give a precipitate of silver hydroxide and then
redissolving the silver hydroxide in ammonia solution giving a basic solution of Ag(NH3)2OH
containing silver(I).) Tollens’ reagent is an oxidizing agent which itself becomes reduced to give
metallic silver (formed as a silver mirror on the sides of the test-tube) when it reacts with the
aldehyde but does not react with the ketone. The reaction is
CH3CH2CHO + Ag+
NH 3 , H 2 O, OH −
→
CH3CH2COOH + Ag (formed as a silver mirror)
In this case the carboxylic acid would be formed as the sodium salt.
-2-
CHEMISTRY 2440
2.
(a)
Use the information provided to draw the structure of the described
compound.
OH
(i)
Ferulic acid (common name) is widely distributed
in plants and is used a food preservative. The
HO
name given to ferulic acid in the reference book is
3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid.
O
O
[8]
(ii)
(iii)
Ethyl amyl ketone (common name) is an
important organic solvent that is narcotic in high
concentrations. The name given to ethyl amyl ketone
in the reference book is 5-methyl-3-heptanone.
CH3
O
CH3
CH3
CH3
Ethchlorvynol (common name) is a sedative and hypnotic
that can be addictive. The name given to ethchlorvynol in HC
the reference book is 1-chloro-3-ethylpent-1-en-4-yn-3-ol.
OH
Cl
CH3
(iv)
Propyl gallate (common name) is used as an antioxidant for foods, fats,
oils, ethers, etc. The name given to propyl gallate in the reference book is
propyl 3,4,5-trihydroxybenzoate.
O
O
CH3
HO
OH
OH
(b)
Elenolide (common name) is extracted from the fruits, bark and
leaves of the olive tree (Olea europaea).
O
H3C
alkene
a
(ii)
CH3
d
e
[4]
c
O
O
(i)
aldehyde
O
lactone
[4]
b
H
O
ester
alkene
On the diagram above circle and name the functional
groups in the molecule
Write a paragraph describing two different chemical
properties or reactions that you would expect of elenolide
Since the compound is and aldehyde it should be easily oxidized using a dilute solution
of potassium dichromate in sulfuric acid. The orange colour of the dichromate ion will be
replaced by the green colour of the chromium-3 ion. The aldehyde group will be
oxidized to the carboxylic acid group. Similarly, it would give a silver mirror with Tollens
test.
Since the compound is an alkene it should decolourize a yellow solution of bromine in
carbon tetrachloride to give a colourless solution of the dibromo compound. The
bromine adds across a double bond to give a dibromo compound.
-3-
CHEMISTRY 2440
3.
(a)
Fill in the blanks in the following reactions with the structure(s) of
the missing reactant(s) and/or product(s). Where indicated, give
the reaction conditions.
CH3
(i)
CH3
O
H3C
CH2
CH
C
CH3
+
CH2
O
CH
H3C
NaOH(aq)
-
H3C
CH2
+
O Na
CH2 CH
CH2 C
+
O
OH
CH
H3C
CH2
CH3
(ii)
+
+
HBr
OH
[10 ]
H2O
Br
(iii)
H2SO4/140 oC
2 CH 3 CH 2 CH 2 OH
CH3CH2CH2OCH2CH2CH3
(reaction conditions)
(an alcohol)
(iv)
CH3CH2CH2CHO
+
Ni catalyst
H2
CH2CH2CH2OH
(v)
CH2
H2C
[3]
CH2
C
CH
(b)
CH3
OH
o
H2SO4/180 C
CH2
H2C
K2Cr2O7/H+(aq)
CH3
CH
CH2
C
O
Explain why aldehydes and
CH3 ketones have lower boiling points than
the alcohols of similar structure and molar mass.
Aldehydes, ketones and alcohols such as propanal, CH3CH2CHO; propanone, CH3COCH3, and
1-propanol, CH3CH2CH2OH are all liquids at room temperature. When a liquid boils the intermolecular
forces that hold the molecules in the liquid phase must be overcome to allow the molecules to enter the
vapour phase. The stronger the intermolecular forces (for similar molecules) the higher the boiling point.
All three of the examples given above are polar molecules so the intermolecular forces are London
dispersion forces and dipole-dipole interactions. However, the alcohol is also able to hydrogen bond to
other alcohol molecules due to the presence of the -OH group and this is an additional strong
intermolecular force that must be overcome when the liquid boils. This leads to the alcohol having a
higher boiling point than the similar mass aldehyde and ketone.
(c)
solution, two layers form, as the ethyl benzoate insoluble in the
aqueous sodium hydroxide. If the mixture of ethyl benzoate and
aqueous sodium hydroxide is allowed to stand for an hour or so a
homogeneous solution forms. Has the ethyl benzoate dissolved?
Explain.
The ethyl benzoate has not dissolved but has reacted with the sodium hydroxide to give water soluble
products. The ethyl benzoate is slowly saponified by the base to give sodium benzoate and ethanol, both
of which are water soluble and thus form a homogeneous solution. The reaction is:
O
O
C
O
CH2
C
CH3
+
-
+
O Na
NaOH(aq)
[3]
-4-
+
OH
CH3CH2