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OCR Chemistry A 11.4 Isomerism Teacher and Technician notes Structural isomerism Specification references 4.1.1 e) M 4.2 Aims This exercise will give the students practise at naming organic molecules. It should in particular help students who have difficulty visualising molecules. Using a modelling kit, students will be able to model isomerism in three dimensions. Learning outcomes After completing the practical students should be able to: understand what is meant by structural isomerism use ideas about structural isomerism to identify and name isomers of alkanes, alcohols, aldehydes, ketones, carboxylic acids, and esters. Teacher notes This exercise is a good way of engaging students with concepts that are hard to visualise. Using molecular modelling kits enables a hands-on approach and can quickly show students how molecules and isomers are formed. Answers for method sheet Molecular formula Structural formula Shortened structural formula IUPAC, or systematic, name 1 C2H6O CH3CH2OH Ethanol 2 CH4 CH4 Methane © Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original 1 OCR Chemistry A 1 2 11.4 Isomerism Teacher and Technician notes 3 C2H6 CH3CH3 Ethane 4 C4H10 CH3CH2CH2CH3 Butane 5 C4H10 CH3CH(CH3)CH3 2-Methylpropane 6 C3H8O CH3CH2CH2OH Propan-1-ol 7 C3H8O CH3CH2(OH)CH3 Propan-2-ol 8 C6H12 (CH2)6 Cyclohexane Molecules 4 and 5 are structural isomers. Molecules 6, 7, and 8 are structural isomers. These molecules are structural isomers because they have the same molecular formulae, but different structural formulae. © Oxford University Press 2015 (1 mark) (1 mark) (1 mark) (1 mark) www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original 2 OCR Chemistry A 3 11.4 Isomerism Teacher and Technician notes Students are likely to give the first four of these isomers of C4H10O. The final two isomers given here are ethers which are not covered in the course. These could be introduced to more able students as an extension to the question. (6 marks) butan-1-ol butan-2-ol 2-methylpropan-1-ol 2-methylpropan-2-ol ethoxyethane methoxypropane © Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original 3 11.4 Isomerism Teacher and Technician notes OCR Chemistry A 4 Award a maxiumum of 5 marks for each of part a and b a Correctly drawn species (as in diagram below) b Correctly named molecules (as in diagram below) (5 marks) (5 marks) Answers for follow up sheet 1 Alkanes are a group of hydrocarbons which have the general formula CnH2+2. a C5H12 b Award 1 mark for each correct structure. c Award 1 mark for each correct name. (1 mark) Skeletal formula Name 2 Pentane 2-methylbutane 2,2-dimethylpropane Award 1 mark for each correct structure, 1 mark for each correct name. Displayed formula Name 3 a Propanal Propanone Draw out the displayed formula and name both of the carboxylic acids which have the molecular formula C4H8O2. (4 marks) Displayed formula of carboxylic acids with the molecular formula C4H8O2 Displayed formula 1 mark for each correct structure Name © Oxford University Press 2015 1 mark for each correct name www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original 4 11.4 Isomerism Teacher and Technician notes OCR Chemistry A b Award 1 mark for each correct structure (4 marks) Displayed formulae of esters with the molecular formula C4H8O2 1 mark for each correct structure 4 a b Award 1 mark for each correctly drawn structure for isomers with formula C3H7Cl. Award 1 mark for each correctly named structure. (4 marks) (4 marks) Support This activity assumes that students have covered the main functional groups in organic chemistry encountered across the whole course including alkanes, alkenes, alcohols, aldehydes, ketones, carboxylic acids, and esters. Although alkenes are not covered in this activity, as they also exhibit stereoisomerism, students could be encouraged to try to work out that cyclic alkanes and aliphatic alkenes are structural isomers of each other. Further ideas to stretch students could include finding all the isomers of cyclic alkanes, for example C4H8 and C5H10. © Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original 5 OCR Chemistry A 11.4 Isomerism Teacher and Technician notes Technician notes Safety There are no safety hazards with this exercise. Equipment and materials The following will be required for each student, or each group of students. Molymod kits or molecular modelling kits © Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original 6