Chapter : Organic Chemistry
June 24, 2012
(i) A compound D has the molecular formula C2H4O2 and is obtained
from a reaction between methanoic acid and methanol. Write an
equation for this reaction and state the name of D.
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(ii) A second compound, E, has the same molecular formula as D and
has acidic properties.
State the name of compound E.
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Ans: (i) CH3OH + HCOOH ----> HCOOCH3 + H2O
for both reactants and [1] for both products
(accept C2H4O2) methyl methanoate;
(ii) ethanoic acid;
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A student prepared a sample of compound Y from benzene as follows:
C6H6 → C6H5CH2CH3 → C6H5CHClCH3
X Y
(a) (i) The first step was the conversion of benzene to compound X,
using chloroethane as the reagent and aluminium chloride as
a catalyst.Write the equation for the reaction and give equations
for the mechanism.
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(ii) Name the type of mechanism that occurs in the second step when
X is converted to Y.
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(b) (i) Draw two structures for compound Y, showing the relationship
between them.
(ii) Explain the term plane-polarized light and describe how the optical
isomers of Y could be distinguished using a polarimeter.
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(iii) Explain why the sample of Y produced by the student did not show
optical activity.
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(c) Samples of compound Y and chlorobenzene are warmed separately with
aqueous sodium hydroxide. State, with a reason, whether compound Y
or chlorobenzene would react more slowly.
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(Total 16 marks)
Ans : (a) (i) C6H6 + CH3CH2Cl ---> C6H5CH2CH3 + HCl;
CH3CH2Cl + AlCl3 ---> CH3CH2+ + AlCl4–;
[1] for arrow
(ii) free radical substitution; 1
(b) (i) one correct structure;
second structure clearly a mirror image;
(ii) light in which all waves/vibrations are in one plane;
plane-polarized light passed through each isomer (solution);
plane of polarization rotates;
in opposite directions for each isomer; 4
(iii) equal amounts of each isomer were formed/racemic mixture formed;
optical activities/rotations cancelled out; 2
(c) chlorobenzene;
nucleophile/OH– repelled by delocalized electrons/carbon atom being
attacked is less electron-deficient/carbon-chlorine bond is stronger; 2
from a reaction between methanoic acid and methanol. Write an
equation for this reaction and state the name of D.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(ii) A second compound, E, has the same molecular formula as D and
has acidic properties.
State the name of compound E.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
Ans: (i) CH3OH + HCOOH ----> HCOOCH3 + H2O
for both reactants and [1] for both products
(accept C2H4O2) methyl methanoate;
(ii) ethanoic acid;
_____________________________________________________________________________________________
A student prepared a sample of compound Y from benzene as follows:
C6H6 → C6H5CH2CH3 → C6H5CHClCH3
X Y
(a) (i) The first step was the conversion of benzene to compound X,
using chloroethane as the reagent and aluminium chloride as
a catalyst.Write the equation for the reaction and give equations
for the mechanism.
............................................................................................................................
............................................................................................................................
(ii) Name the type of mechanism that occurs in the second step when
X is converted to Y.
............................................................................................................................
(b) (i) Draw two structures for compound Y, showing the relationship
between them.
(ii) Explain the term plane-polarized light and describe how the optical
isomers of Y could be distinguished using a polarimeter.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(iii) Explain why the sample of Y produced by the student did not show
optical activity.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(c) Samples of compound Y and chlorobenzene are warmed separately with
aqueous sodium hydroxide. State, with a reason, whether compound Y
or chlorobenzene would react more slowly.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(Total 16 marks)
Ans : (a) (i) C6H6 + CH3CH2Cl ---> C6H5CH2CH3 + HCl;
CH3CH2Cl + AlCl3 ---> CH3CH2+ + AlCl4–;
[1] for arrow
(ii) free radical substitution; 1
(b) (i) one correct structure;
second structure clearly a mirror image;
(ii) light in which all waves/vibrations are in one plane;
plane-polarized light passed through each isomer (solution);
plane of polarization rotates;
in opposite directions for each isomer; 4
(iii) equal amounts of each isomer were formed/racemic mixture formed;
optical activities/rotations cancelled out; 2
(c) chlorobenzene;
nucleophile/OH– repelled by delocalized electrons/carbon atom being
attacked is less electron-deficient/carbon-chlorine bond is stronger; 2
Posted by Noor Syazlin Naim.