BS 132 Academy of Chinese Culture and Health Sciences Organic Chemistry

BS132 RESIT COURSEWORK 2019-201. A 12 ml sample of 1-chlorobutane (CH3CH2CH2CH2Cl; density = 0.89 g ml-1) is
reacted with an excess of methoxide under conditions that result in an SN2
nucleophilic substitution reaction.
(a) Draw and name the ether that is formed in this reaction.
0.5 marks
(b) If 8.7 ml of the ether (density = 0.74 g ml-1) is obtained after purification,
calculate the percentage yield of the reaction.
4 marks
(c) Draw the mechanism for this reaction, including the transition state.
2 marks
(d) Draw an energy diagram for this reaction, assuming that it is exergonic.
1.5 marks
(e) The relative rates observed for the SN2 reaction between methoxide and 1chlorobutane employing either methanol or dimethylformamide as the solvent are
given below. Explain the difference in relative rates.
4 marks
O
MeOH
solvent
H
N
Me
Me
relative
rate
3.3 x 103
1
(f) The relative rates observed for the SN2 reactions between methoxide and
chloroethane, 2-chloropropane or 2-chloro-2-methylpropane are given below.
Explain the differences in relative rates.
3 marks
reactant
CH3CH2Cl
relative
rate
1
(CH3)2CHCl
(CH3)3CCl
3.3 x 10-2
7.2 x 10-4
(g) The relative rates observed for the SN2 reactions between methoxide and 1bromobutane or 1-chlorobutane are given below. Explain the difference in
relative rates, given that the pKa values for HBr and HCl are -9 and -7
respectively.
4 marks
reactant
relative
rate
CH3CH2CH2CH2Br
1
1
CH3CH2CH2CH2Cl
3.6 x 10-2
BS132 RESIT COURSEWORK 2019-20
2. (a) The E2 reaction between methoxide and 2-chloropentane (below) gives the
isomers (I), (II) and (III). Explain how these products are formed and why the
relative abundances are (I) > (II) > (III).
5 marks
Cl
-HCl
CH3O
H3C
+
CH3CHCH2CH2CH3
H
H
+
CH2CH3
(I)
H
H
H3C
+
CH2CH3
(II)
H
H
H
CH2CH2CH3
(III)
(b) 2-chloropropane is reacted with ethanol under conditions that result in an E1
elimination reaction.
H
H3C
Cl
2-chloropropane
CH3
(i) Draw and name the alkene that is formed in this reaction.
0.5 marks
(ii) Draw the mechanism for this reaction and indicate the rate determining step.
2 marks
(iii) Draw an energy diagram for this reaction, assuming that it is exergonic.
1.5 marks
(c) The RMM of 2-chloropropane is 78.55 g mol-1 and it has a density of 0.86 g ml-1
(i) How many pmol of 2-chloropropane are present in a 65 ng sample?
2 marks
(ii) How many mg of 2-chloropropane are present in a 35 l sample?
2 marks
(iii) What is the volume occupied, in litres, by 5.5 moles of 2-chloropropane?
2 marks
2
BS132 RESIT COURSEWORK 2019-20
3.
The electrophilic addition reaction of trans-but-2-ene with hydrogen bromide
produces 2-bromobutane (below).
Me
Me H
H
+
H
HBr
H
Br
Me
Me
H
(a) Draw a mechanism for this reaction.
2 marks
(b) Draw an energy diagram for this reaction, assuming that it is exergonic.
2 marks
(c) The electrophilic addition reaction of 1-methylcyclohexene with hydrogen
bromide (below) can in theory give the constitutional isomers (I) and (II).
Explain why (I) is the only product formed.
3 marks
Br
CH3
+
CH3
CH3
+
HBr
Br
(II)
0%
(I)
100%
(d) The electrophilic addition reaction of 3-methyl-1-butene with hydrogen
bromide (below) forms constitutional isomers (III) and (IV). Explain how
these products are formed.
5.5 marks
CH3
CH3
H3C
CH
C
H
H
HBr
H3C
CH
H
C
Br
C
Br
C
H
H
H3C
H
+
CH3
C
H
H
H
C
C
H
H
H
(III)
(IV)
MINOR PRODUCT
MAJOR PRODUCT
(e) The electrophilic addition reaction of propene with bromine produces 1,2dibromopropane (below). Draw a mechanism for this reaction, including the
bromonium ion intermediate.
2 marks
Me
Me H
H
+
H
Br2
Br
H
Br
H
3
H
BS132 RESIT COURSEWORK 2019-20
4. The electrophilic substitution reaction of benzene with bromine produces
bromobenzene (below).
Br
+
+
Br2
HBr
(a) Draw a mechanism for this reaction.
2 marks
(b) Draw an energy diagram for this reaction, given that it is exergonic.
2 marks
(c) Explain how ferric bromide, FeBr3, acts as a catalyst for this reaction.
2 marks
(d) Explain why an electrophilic substitution reaction between benzene and
bromine occurs in preference to the electrophilic addition reaction shown
below.
2 marks
Br
Br
+
Br2
(e) The electrophilic substitution reaction of ethylbenzene with bromine
(below) gives the isomers (I), (II) and (III). Explain how these products
are formed and why the relative abundances are (I) > (III) > (II).
7 marks
Br
+
+
+
Br2
Br
Br
(I)
(II)
(III)
55%
5%
40%
4
BS132 RESIT COURSEWORK 2019-20
5. A 22 ml sample of 2-pentanone (density = 0.81 g ml-1) is reacted with an
excess of borohydride in anhydrous THF, then water is added to the mixture
(see below).
(i) BH4-
O
(ii) H2O
(a) Draw and name the alcohol that is formed in this reaction.
0.5 marks
(b) If 13.7 g of the alcohol is obtained after purification, calculate the
percentage yield of the reaction.
4 marks
(c) Draw the mechanism for this reaction.
2 marks
6. A 17 ml sample of cyclohexanone (density = 0.95 g ml-1) is reacted with an
excess of methyl magnesium bromide in anhydrous THF, then water is added to
the mixture (see below).
(i) MeMgBr
O
(ii) H2O
(a) Draw and name the alcohol that is formed in this reaction.
0.5 marks
(b) If 11.3 ml of the alcohol (density = 0.92 g ml-1) is obtained after
purification, calculate the percentage yield of the reaction.
4 marks
(c) Draw the mechanism for this reaction.
2 marks
7. (a) Draw a mechanism for the formation of a hemiacetal from the reaction of
pentanal with 1-pentanol.
2 marks
(b) Draw a mechanism for the formation of a hemiketal from the reaction of
butanone with 2-butanol.
2 marks
5
BS132 RESIT COURSEWORK 2019-20
8. A 12 ml sample of butanoic acid (CH3CH2CH2CO2H; density = 0.96 g ml-1)
is reacted with an excess of methanol with sulfuric acid present.
(a) Draw and name the ester that is formed in this reaction.
0.5 marks
(b) If 9.2 ml of the ester (density = 0.90 g ml-1) is obtained after
purification, calculate the percentage yield of the reaction.
3 marks
(c) Draw the mechanism for this reaction.
2 marks
(d) Explain how the sulfuric acid acts as a catalyst for this reaction. 2 marks
(e) What volume of butanoic acid, in l, is required to make 25 ml of a 20
mM aqueous solution?
2 marks
9. A 15 ml sample of phenylacetyl chloride (density = 1.17 g ml-1) is reacted
with an excess of diisopropylamine to give an amide product (below).
Cl
O
N
-HCl
+
N
H
O
If 16 g of the amide is obtained after purification, calculate the percentage yield
of the reaction.
6 marks
10. A 2.5 g sample of citric acid (below) is dissolved in water to give a 100 ml
solution. Calculate the volume of 250 mM NaOH solution that would have to
be added to neutralise 25 ml of the citric acid solution.
4 marks
OH CO H
2
CITRIC ACID
HO2C
CO2H
6

Get your paper done on time by an expert in your field.

Order Now