14.2. Alkenes
A subsection of Chemistry, 9701, through 14. Hydrocarbons
Listing 10 of 191 questions
(CH3)3CCHO is used in the synthesis of some antibiotics. Give the name of (CH3)3CCHO. State the hybridisation of the carbon atom labelled with an asterisk, *. CH3 CH3 H3C C C O H * Two reaction sequences are shown. CH3 CH3 NaBH4 H3C C S (CH3)3CCO2H A U C O H T reaction 2 reaction 3 reaction 1 O O Reaction1 is an oxidation reaction. Identify the reagentand conditions for reaction1. A, (CH3)3CCO2H, is a solid at room temperature. B, CH3CO2(CH2)2CH3, is an isomer of A. B is a liquid at room temperature. Explain the difference in the physical states of A and B, with reference to any intermolecular forces that may exist. Give the balanced equation for the reaction of (CH3)3CCHO with NaBH4 to form S. Use to represent an atom of hydrogen provided by NaBH4. Draw the structure of the organic molecule T that reacts with A, (CH3)3CCO2H, in reaction2, to form U. Suggest a catalyst for reaction2. T catalyst  X, Y and Z are all isomers of (CH3)3CCHO. A summary of some of the reactions and properties of X, Y and Z is shown in the table. compound observations with 2,4-DNPH observations with Fehling’s solution principal absorptions in infra-red spectrum X no reaction 1715 cm–1 Y red precipitate 1730 cm–1 Z no reaction no reaction 3200–3600 cm–1 1630 cm–1 1050 cm–1 X and Y each contains a carbonyl group. Complete the table with the expected observations for the reactions of X and Y with 2,4‑DNPH. Identify the functional group present in Y that causes the recorded observation with Fehling’s solution. Y has a chiral centre and exists as a pair of optical isomers. State what is meant by the term chiral centre. Draw the optical isomers of Y using the conventional three-dimensional representation.  Z, C5H10O, has a branched carbon chain. It shows geometrical isomerism. Complete the table with the bond responsible for each of the principal absorptions seen in the infra-red spectrum of Z. principal absorptions in infra-red spectrum bond responsible 3200–3600 cm–1 1630 cm–1 1050 cm–1  Draw the skeletal formula of Z.  X contains a carbonyl group. X reacts with HCN, in the presence of a small amount of NaCN, to form (C2H5)2C(OH)CN as shown. X + HCN (C2H5)2C(OH)CN Draw the mechanism of the reaction of X with HCN. ● Draw the structure of X and the intermediate. ● Include all charges, partial charges, lone pairs and curly arrows. C C2H5 C2H5 HO NC  State the role of NaCN in the reaction in . 
9701_w19_qp_21
THEORY
2019
Paper 2, Variant 1
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(CH3)3CCHO is used in the synthesis of some antibiotics. Give the name of (CH3)3CCHO. State the hybridisation of the carbon atom labelled with an asterisk, *. CH3 CH3 H3C C C O H * Two reaction sequences are shown. CH3 CH3 NaBH4 H3C C S (CH3)3CCO2H A U C O H T reaction 2 reaction 3 reaction 1 O O Reaction1 is an oxidation reaction. Identify the reagentand conditions for reaction1. A, (CH3)3CCO2H, is a solid at room temperature. B, CH3CO2(CH2)2CH3, is an isomer of A. B is a liquid at room temperature. Explain the difference in the physical states of A and B, with reference to any intermolecular forces that may exist. Give the balanced equation for the reaction of (CH3)3CCHO with NaBH4 to form S. Use to represent an atom of hydrogen provided by NaBH4. Draw the structure of the organic molecule T that reacts with A, (CH3)3CCO2H, in reaction2, to form U. Suggest a catalyst for reaction2. T catalyst  X, Y and Z are all isomers of (CH3)3CCHO. A summary of some of the reactions and properties of X, Y and Z is shown in the table. compound observations with 2,4-DNPH observations with Fehling’s solution principal absorptions in infra-red spectrum X no reaction 1715 cm–1 Y red precipitate 1730 cm–1 Z no reaction no reaction 3200–3600 cm–1 1630 cm–1 1050 cm–1 X and Y each contains a carbonyl group. Complete the table with the expected observations for the reactions of X and Y with 2,4‑DNPH. Identify the functional group present in Y that causes the recorded observation with Fehling’s solution. Y has a chiral centre and exists as a pair of optical isomers. State what is meant by the term chiral centre. Draw the optical isomers of Y using the conventional three-dimensional representation.  Z, C5H10O, has a branched carbon chain. It shows geometrical isomerism. Complete the table with the bond responsible for each of the principal absorptions seen in the infra-red spectrum of Z. principal absorptions in infra-red spectrum bond responsible 3200–3600 cm–1 1630 cm–1 1050 cm–1  Draw the skeletal formula of Z.  X contains a carbonyl group. X reacts with HCN, in the presence of a small amount of NaCN, to form (C2H5)2C(OH)CN as shown. X + HCN (C2H5)2C(OH)CN Draw the mechanism of the reaction of X with HCN. ● Draw the structure of X and the intermediate. ● Include all charges, partial charges, lone pairs and curly arrows. C C2H5 C2H5 HO NC  State the role of NaCN in the reaction in . 
9701_w19_qp_23
THEORY
2019
Paper 2, Variant 3
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Some reactions of compoundG are shown. OH H O G OH HO O reaction 3 reaction 4 H2SO4, heat under reflux HOOC(CH2)2COOH Tollens’ reagent reaction 2 reaction 1 Na H O O State the type of reaction that occurs in reaction1. Suggest the reagentand conditions required for reaction1. Draw the structure of the organic product, H, from reaction2.  State what you would observe in reaction3. Give the type of reaction shown by reaction4. G and J are structural isomers of each other. OH H O G H O OH J Name the type of structural isomerism shown by G and J. Suggest one chemical test that can distinguish G from J. Give the result of the test with each compound. test result with G result with J  In the reaction schemes below, G and J are converted into organic compoundK. G K NaBH4 HO(CH2)3CH2OH Al 2O3 heat Al 2O3 heat J NaBH4 HO(CH2)2CH(OH)CH3 State the role of NaBH4 in the reactions with G and J. Identify the organic product K. P and Q have the same molecular formula as G. HO O P OH O Q Complete the table with the expected observations for the reactions of P and Q with the named reagents. reagent result with P result with Q Br22,4-dinitrophenylhydrazine aqueous sodium carbonate  The structure of compoundL is shown. R represents a hydrocarbon chain. O L O R A student was asked to deduce the full structure of L. The student analysed L using infrared spectroscopy. The following spectrum was obtained. transmittance % wavenumber / cm–1 Z X Y Identify the bonds responsible for the absorptions marked X and Z. X Z  AbsorptionY shows that L has a C=C bond present in the R group. The student decided to treat L with hot concentrated acidified potassiummanganate(. The products of the reaction are shown. O L O R O O O hot concentrated acidified KMnO4 OH + M CH3(CH2)4COOH Name M. Use the information in to deduce the molecular formula of L.  molecular formula of L = 
9701_w20_qp_22
THEORY
2020
Paper 2, Variant 2
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Benzene, C6H6, can be obtained from crude oil. Benzene reacts with bromine, in the presence of a suitable catalyst, forming bromobenzene as one product. Give the name or formula of the other product of this reaction. In the presence of the catalyst, bromine can be considered to form the electrophile Br+. Complete the mechanism by which benzene reacts with Br+, using curly arrows to show the movement of electron pairs. intermediate Br Br+ + H+  Name this mechanism. Benzene can be used as a starting material in the synthesis of cyclohexylmethanol, C6H11CH2OH, as outlined below. benzene A CH2CH3 step 1 step 3 step 2 cyclohexylmethanol CH2OH CH2OH step 4 KMnO4 + OH–heat Identify a suitable reagent and a suitable catalyst for step1. reagent catalyst  Draw the structure of A. A  Identify suitable reagents for steps3 and 4. step 3 step 4  Deduce the number of peaks in the carbon‑13 NMR spectrum of cyclohexylmethanol. 
9701_w20_qp_41
THEORY
2020
Paper 4, Variant 1
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Describe the structure of a benzene molecule, C6H6. Your answer should include: ● the shape of the molecule ● the relative lengths of the C–C bonds ● bond angles ● the hybridisation of the carbon atoms ● the overlap between orbitals that produces each type of bond present. Benzene can be used as a starting material to produce phenylamine by a two-step synthesis. benzene nitrobenzene phenylamine NO2 NH2 step 1 step 2 Step1 is the reaction of benzene with NO2 + ions. Complete the mechanism and draw the intermediate of step1. Include all relevant charges and curly arrows to show the movement of electron pairs. intermediate nitrobenzene + H+ +NO2  State the name of the mechanism in . Identify the reagents needed to produce NO2 + ions. Write an equation to explain how these reagents produce NO2 + ions. Give reagents and conditions for the production of phenylamine from nitrobenzene in step2. Phenylamine reacts with Br2. Write an equation for this reaction. You may use structural or displayed formulae. Name the organic product of this reaction. Describe two observations that can be seen when phenylamine reacts with Br2. observation 1 observation 2  Describe the relative basicities of ammonia, ethylamine and phenylamine, starting with the least basic. Explain your answer in terms of their structures. least basic most basic  1,3‑diaminopropane, H2NCH2CH2CH2NH2, can be used to make polyamides. Identify one compound that would react with 1,3‑diaminopropane to form a polyamide. Draw a section of the polymer chain formed from 1,3‑diaminopropane and the compound you chose in . Your answer should: ● include four monomer residues (two of each type of monomer) ● show the amide link fully displayed ● clearly identify one repeat unit of this polymer.  
9701_w20_qp_42
THEORY
2020
Paper 4, Variant 2
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Benzene, C6H6, can be obtained from crude oil. Benzene reacts with bromine, in the presence of a suitable catalyst, forming bromobenzene as one product. Give the name or formula of the other product of this reaction. In the presence of the catalyst, bromine can be considered to form the electrophile Br+. Complete the mechanism by which benzene reacts with Br+, using curly arrows to show the movement of electron pairs. intermediate Br Br+ + H+  Name this mechanism. Benzene can be used as a starting material in the synthesis of cyclohexylmethanol, C6H11CH2OH, as outlined below. benzene A CH2CH3 step 1 step 3 step 2 cyclohexylmethanol CH2OH CH2OH step 4 KMnO4 + OH–heat Identify a suitable reagent and a suitable catalyst for step1. reagent catalyst  Draw the structure of A. A  Identify suitable reagents for steps3 and 4. step 3 step 4  Deduce the number of peaks in the carbon‑13 NMR spectrum of cyclohexylmethanol. 
9701_w20_qp_43
THEORY
2020
Paper 4, Variant 3
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Questions Discovered
191