1. 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.
(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.
- Draw the mechanism for this reaction, including the transition state.
- Draw an energy diagram for this reaction, assuming that it is exergonic.
(e) The relative rates observed for the SN2 reaction between methoxide and 1-chlorobutane employing either methanol or dimethylformamide as the solvent are given below. Explain the difference in relative rates.
(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.
- The relative rates observed for the SN2 reactions between methoxide and 1-bromobutane 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.
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).
(b) 2-chloropropane is reacted with ethanol under conditions that result in an E1 elimination reaction.
(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 ml sample? 2 marks
(iii) What is the volume occupied, in litres, by 5.5 moles of 2-chloropropane?
2 marks
3. The electrophilic addition reaction of trans-but-2-ene with hydrogen bromide produces 2-bromobutane (below).
- Draw a mechanism for this reaction.
- Draw an energy diagram for this reaction, assuming that it is exergonic.
- 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.
(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.
(e) The electrophilic addition reaction of propene with bromine produces 1,2-dibromopropane (below). Draw a mechanism for this reaction, including the bromonium ion intermediate.
4. The electrophilic substitution reaction of benzene with bromine produces bromobenzene (below).
- Draw a mechanism for this reaction.
- Draw an energy diagram for this reaction, given that it is exergonic.
- Explain how ferric bromide, FeBr3, acts as a catalyst for this reaction.
- Explain why an electrophilic substitution reaction between benzene and bromine occurs in preference to the electrophilic addition reaction shown below.
(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).
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).
(a) Draw and name the alcohol that is formed in this reaction.
(b) If 13.7 g of the alcohol is obtained after purification, calculate the percentage yield of the reaction.
- Draw the mechanism for this reaction.
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).
(a) Draw and name the alcohol that is formed in this reaction.
(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.
(c) Draw the mechanism for this reaction.
7. (a) Draw a mechanism for the formation of a hemiacetal from the reaction of pentanal with 1-pentanol.
(b) Draw a mechanism for the formation of a hemiketal from the reaction of butanone with 2-butanol.
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.
(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.
(c) Draw the mechanism for this reaction.
(d) Explain how the sulfuric acid acts as a catalyst for this reaction.
(e) What volume of butanoic acid, in ml, is required to make 25 ml of a 20 mM aqueous solution?
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).
If 16 g of the amide is obtained after purification, calculate the percentage yield of the reaction.
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.
