Suggested answers to in-text activities and unit-end exercises Topic 8 Unit 30

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1 Suggested answers to in-text activities and unit-end exercises In-text activities Checkpoint (page 60) 1 Any two of the following: 2 a) A 2-bromo-2-methylpropane B 1-bromobutane b) 3 4 a) position isomers b) functional group isomers Checkpoint (page 63) 1 2 a) Structural formula of 1,1-dibromoethene: Suggested answers to in-text activities and unit-end exercises 1 Jing Kung. All rights reserved.

2 The compound does not exhibit goemetrical isomerism. One of the carbon of the C=C bond has identical hydrogen / bromine atoms attached to it. b) Structural formula of ethene-1,2-diol: The compound can exhibit geometrical isomerism. Two different groups are attached to each carbon of the C=C bond. 3 a) b) Geometrical isomerism Checkpoint (page 66) 1 In addition to intermolecular attractions, the melting point of a compound depends also on the degree of compactness of molecules in the solid state. The cis isomer has a lower degree of symmetry. It fits into a crystalline lattice relatively poorly and thus has a lower melting point. 2 In a molecule of X, due to the close proximity of the OH group and CHO group, intramolecular hydrogen bonds are readily formed. Thus intermolecular hydrogen bonds between the molecules of X are less extensive. Molecules of Y forms more intermolecular hydrogen bonds than molecules of X do. the melting point of Y is much higher than that of X. Suggested answers to in-text activities and unit-end exercises 2 Jing Kung. All rights reserved.

3 Checkpoint (page 68) a) achiral b) chiral c) chiral Checkpoint (page 76) 1 a) i) ii) It is chiral. iii) b) i) ii) It is chiral. Suggested answers to in-text activities and unit-end exercises 3 Jing Kung. All rights reserved.

4 iii) 2 a) Identical Rotation of the second molecule about the C CH 3 bond produces the molecule shown below: the second molecule is identical to the first one. b) The mirror image of the first molecule is shown below: Suggested answers to in-text activities and unit-end exercises 4 Jing Kung. All rights reserved.

5 Rotation of the mirror image about the C H bond produces the second molecule. The two given molecules are not superposable. the two given molecules are non-superposable mirror images of each other; i.e. they are enantiomers. c) The mirror image of the first molecule is shown below: The first molecule and its mirror image are not superposable. Rotation of the mirror image about the C F bond produces the second molecule. the two given molecules are non-superposable mirror images of each other; i.e. they are enantiomers. Suggested answers to in-text activities and unit-end exercises 5 Jing Kung. All rights reserved.

6 3 a) The compound exhibits stereoisomerism. Its molecule contains a chiral carbon. Enantiomers: b) No There is no carbon atom with four different atoms or groups of atoms attached to it. c) Geometrical isomerism Checkpoint (page 79) 1 a) Identical b) The mirror image of the first molecule is shown below: The first molecule and its mirror image are not superposable. Suggested answers to in-text activities and unit-end exercises 6 Jing Kung. All rights reserved.

7 Rotation of the mirror image produces the second molecule. the two molecules are non-superposable mirror images of each other; i.e. their relationship is enantiomeric. c) Geometrically isomeric d) Structurally isomeric 2 a) It contains a carbon atom with four different groups attached. b) Higher doses are required. The other stereoisomers may have harmful side effects. Suggested answers to in-text activities and unit-end exercises 7 Jing Kung. All rights reserved.

8 Unit-end exercises (pages 83 91) Answers for the HKCEE (Paper 1) and HKALE questions are not provided. 1 2 a) C 4 H 10 b) C 2 H 5 O c) B and E d) A and F 3 a) carbon-carbon double bond carboxyl group Suggested answers to in-text activities and unit-end exercises 8 Jing Kung. All rights reserved.

9 b) 4 a) b) c) 5 a) The molecule contains one carbon atom bonded to four different groups of atoms. b) Suggested answers to in-text activities and unit-end exercises 9 Jing Kung. All rights reserved.

10 6 B 7 C Option A Both CH 3 COOCH 2 CH 3 and CH 3 CH 2 COOCH 3 contain an ester functional group ( ). Option B Both (CH 3 ) 2 CHCH(CH 3 ) 2 and (CH 3 ) 3 CCH 2 CH 3 are alkanes. Option C H 2 NCH 2 CH 2 CH 2 COOH contains a carboxyl group ( ) while H 2 NCH 2 COOCH 2 CH 3 contains an ester functional group ( ). Option D Both ClCH 2 CH 2 CH=CH 2 and CH 3 CH=CHCH 2 Cl contain carbon-carbon double bond. 8 A 9 B 10 C Option C The two isomers are enantiomers. They have identical boiling point. 11 A 12 A (1) The molecule is chiral. It has enantiomers. Suggested answers to in-text activities and unit-end exercises 10 Jing Kung. All rights reserved.

11 (2) Identical methyl groups are attached to one of the carbon atoms of the C=C bond. Hence the compound does NOT have stereoisomers. (3) Identical chloro groups are attached to one of the carbon atoms of the C=C bond. Hence the compound does NOT have stereoisomers. 13 D (1) The pair of molecules are identical. (2) The molecules are geometrical isomers. (3) The molecules are position isomers. 14 a) Compound A contains a carbon-carbon double bond. Any one of the following: Suggested answers to in-text activities and unit-end exercises 11 Jing Kung. All rights reserved.

12 Compound B does not contain a carbon-carbon double bond. It should be a cyclic compound. Any one of the following: b) The following structures have the molecular formula C 3 H 6 Cl 2. Structure W has a chiral carbon. It shows optical activity. Thus compound C should have this structure. The other three structures have NO chiral carbon. They do not show optical activity. Thus these are possible structures of compound D. 15 a) 3-bromohexane b) There is restricted rotation about a carbon-carbon double bond. Two different groups are attached to each carbon of the double bond. c) The product contains only single bonds. There is free rotation and NO cis-trans isomers exist. 16 a) Suggested answers to in-text activities and unit-end exercises 12 Jing Kung. All rights reserved.

13 b) Isomer A is methylpropan-2-ol. c) Isomer B is butan-2-ol a) carbon-carbon double bond hydroxyl group b) i) Stereoisomers have their atoms linked in the same way, but they differ in the spatial arrangement of their atoms. ii) Geometrical isomerism iii) Due to the restricted rotation about a carbon-carbon double bond. iv) Identical methyl groups are attached to one of the carbon atoms of one of the C=C bonds. 21 a) b) i) Geometrical isomerism ii) The compounds shown below exhibit structural isomerism. Structural isomers have the same molecular formula but differ in the order in which atoms are linked. Suggested answers to in-text activities and unit-end exercises 13 Jing Kung. All rights reserved.

14 Examples: The compounds shown below exhibit stereoisomerism. Stereoisomers have their atoms linked in the same way, but they differ in the spatial arrangement of their atoms. The following two compounds are geometrical isomers. They have a different arrangement of their atoms in space due to the restricted rotation about a carbon-carbon double bond. Compounds with two different groups attached to each carbon of the double bond have two alternative structures, which are geometrical isomers. Suggested answers to in-text activities and unit-end exercises 14 Jing Kung. All rights reserved.