13.4. Isomerism: structural isomerism and stereoisomerism
A subsection of Chemistry, 9701, through 13. An introduction to AS Level organic chemistry
Listing 10 of 155 questions
There are seven structural isomers with the molecular formula C5H10O that are carbonyl compounds. Four of these are aldehydes. These four aldehydes, A, B, C and D, have the following properties. ● Aldehyde A has a straight chain while B, C and D are branched. ● Aldehyde B is the only one of the four isomers with a chiral centre and it exists as a pair of optical isomers. ● Aldehyde C has two methyl groups in its structure but D has three. Give the structure of each of the four isomers. A B C D Draw the three-dimensional structures of the two optical isomers of B. Describe a chemical test that would allow you to distinguish between any of the four isomers A to D and any of the other three structural isomers of C5H10O, that are carbonyl compounds. In your answer you should describe any necessary reagents and conditions as well as explaining what you would see in each case. Describe a test that would give the same result with all seven carbonyl isomers of C5H10O.
9701_s15_qp_22
THEORY
2015
Paper 2, Variant 2
View
A, B, C, D, E and F are all structural isomers with the molecular formula C4H8O. A, B and C all give an orange precipitate when treated with 2,4-DNPH but only A and B give a brick-red precipitate when warmed with Fehling’s solution. Draw the skeletal formulae of A, B and C. A B C Name the type of structural isomerism shown by A and B. State what you would see when a sample of A is warmed with Tollens’ reagent. D, E and F all decolourise bromine and effervesce slowly with sodium metal. E shows geometrical isomerism. Only D has a branched chain. None of these isomers contains an oxygen atom bonded to a carbon atom involved in π bonding. None of these isomers contains a chiral centre. Give the structures of D, E and F. Show the two stereoisomers of E and label the stereoisomerism shown. D E E F Identify the gas produced during the reaction of each of these isomers with sodium metal. Another compound, G, C3H6O, contains the same functional group as A. Give equations for the reactions of G with each of acidifi ed potassium dichromate(and sodium tetrahydridoborate, NaBH4, using or as appropriate. reaction with acidifi ed potassium dichromate(C3H6O + → reaction with NaBH4 C3H6O + →
9701_s15_qp_23
THEORY
2015
Paper 2, Variant 3
View
A, B and C all have the formula C4H8. They all decolourise bromine and are structural isomers of each other. State the name of the process by which A, B and C could be obtained from C10H22. Draw the structures of these three structural isomers. Only A shows geometrical isomerism. Explain the meaning of the term geometrical isomerism. Draw the displayed formula of A and use it to show the mechanism of the reaction of A with HBr. Include all necessary charges, dipoles, lone pairs and curly arrows. B does not show geometrical isomerism. B reacts with HBr to form a mixture of two structural isomers, X and Y. B + HBr X (has a chiral centre and is produced in higher yield than Y) Y (does not have a chiral centre) State the meaning of the term chiral centre. Name B. X exists as a pair of optical isomers. Draw these isomers using the conventional three-dimensional representation. Explain why X is produced in higher yield than Y. C does not show geometrical isomerism. C reacts with HBr to form a mixture of two structural isomers, neither of which has a chiral centre. Name C. Draw the displayed formula of each of the structural isomers produced by the reaction of C with HBr.
9701_s17_qp_23
THEORY
2017
Paper 2, Variant 3
View
Questions Discovered
155