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14. Hydrocarbons
A section of Chemistry, 9701
Listing 10 of 313 questions
Liquids that contain molecules of T smell like lemons. O T Molecules of T exist as a pair of stereoisomers. Name the type of stereoisomerism shown by molecules of T. Explain your answer. Two organic products are produced when a sample of T is heated under reflux with excess acidified concentrated KMnO4. Draw the structure of the two organic products, from this reaction, in the boxes. organic product 1 organic product 2  Fig.3.2 shows two reactions of T. O O OH T OH S Q R reaction 1 reaction 2 O + HO Identify a suitable reagent for reaction1. Identify the reagent and conditions needed for reaction2. Suggest which product formed in reaction2 has a higher yield. Explain your answer. Separate samples of Q and R are added to separate test-tubes containing acidified K2Cr2O7and heated. O OH Q R O HO Predict the observations for each test-tube. Explain your answer in terms of the functional groups present in Q and R. When PCl 5is added to separate samples of Q and R at room temperature, both react vigorously. Complete the equation shown in to describe the reaction that occurs when R reacts with PCl 5. O OH + PCl 5 R  Suggest why samples of Q and R must be dried before PCl 5 is added. Include a relevant equation to support your answer. 
9701_s22_qp_21
THEORY
2022
Paper 2, Variant 1
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Compare the relative acidities of ethanol, ethanoic acid, chloroethanoic acid and phenol. Explain your reasoning. > > > most acidic least acidic  An excess of ethanedioicacid, HOOCCOOH, is reacted with warm acidified KMnO4. State the type of reaction undergone by ethanedioicacid. Describe what you would observe. Write an equation for this reaction. Your equation can use or as necessary. type of reaction observations equation  A section of a polyester is shown. O C O CH2 CH3 O C CH O O polyester C O CH2 CH3 O C CH O Draw the structures of the two monomers that form this polyester.  Serine can polymerise to form two different types of condensation polymer; a polyester and a polypeptide. H2C H2N C serine H C O OH OH Draw the structure of the polypeptide showing two repeat units. The peptide linkage should be shown displayed.  Explain why condensation polymers normally biodegrade more readily than addition polymers. 
9701_s22_qp_42
THEORY
2022
Paper 4, Variant 2
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Methylbenzene can undergo different reactions, as shown in . reaction 1 H2 / Pt Br2 / UV light Br2 / FeBr3 + reaction 2 reaction 3 Draw structures in for the possible organic products of the three reactions shown. Complete Table 5.1. Table 5.1 type of reaction mechanism reaction 1 reaction 2 When methylbenzene reacts with an electrophile, a substitution reaction occurs. No addition reaction takes place under these conditions. Explain why no addition reaction takes place. The reaction of methylbenzene with thionyl bromide, SOBr2, in the presence of an iron(bromide catalyst, FeBr3, is shown in . FeBr3 + SOBr2 + HBr S O Br The mechanism of this reaction is similar to that of the bromination of benzene. The first step of the mechanism generates the SOBr+ electrophile, as shown. SOBr2 + FeBr3 SOBr+ + FeBr4 – The reaction of methylbenzene with SOBr+ ions is shown in . Complete the mechanism in . Include all relevant curly arrows and charges. Draw the structure of the organic intermediate. S+ O Br intermediate + S O Br The reaction shown in produces a small amount of a by-product, P, with the molecular formula C14H14OS. Suggest a structure for by-product P. Acyl bromides, RCOBr, can be synthesised by the reaction of a carboxylic acid and SOBr2. This is a similar reaction to the synthesis of acyl chlorides using SOCl 2. Give an equation for the reaction between ethanoic acid and SOBr2. Suggest the relative ease of hydrolysis of acyl bromides, RCOBr, acyl chlorides, RCOCl, and alkyl chlorides, RCl. Explain your answer. > > easiest to hydrolyse hardest to hydrolyse
9701_s23_qp_42
THEORY
2023
Paper 4, Variant 2
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Hydrocarbon molecules contain covalent bonds. Define covalent bond. A C=C bond in an alkene is made from a σ bond and a π bond. Identify the hybridisation of the carbon atoms in a C=C bond in an alkene. Draw labelled diagrams to show, in terms of orbital overlap, how the σ and π bonds are made in a C=C bond. σ bond π bond In electrophilic reactions involving alkenes the π bond of C=C is broken. Suggest one difference between σ and π bonds that explains why the π bond is broken in electrophilic addition reactions involving alkenes. Complete to show the mechanism for the electrophilic addition of hydrogen bromide to 2-methylpropene to produce the major organic product. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. CH3 H CH3 H C C H Br
9701_s24_qp_21
THEORY
2024
Paper 2, Variant 1
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State what is meant by partition coefficient, Kpc. The partition coefficient, Kpc, for a compound, X, between carbon disulfide, CS2, and water is 10.5. 1.85 g of X is dissolved in water and made up to 100.0 cm3 in a volumetric flask. 40.0 cm3 of this aqueous solution is shaken with 25.0 cm3 of CS2. The mixture is left to reach equilibrium. Calculate the mass of X, in g, extracted into the CS2 layer. mass of X = g The compound C6H6 has many structural isomers. Four suggested structures of C6H6 are shown in . delocalised benzene Kekulé benzene Dewar benzene Ladenburg benzene Using , complete Table 6.1 to predict the number of carbon atoms that have sp, sp2 and sp3 hybridisation in Kekulé benzene, Dewar benzene and Ladenburg benzene. Table 6.1 C6H6 structure sp hybridised sp2 hybridised sp3 hybridised Kekulé benzene Dewar benzene Ladenburg benzene Describe the shape of delocalised benzene. Include the geometry of each carbon, the C-C-H bond angle and the type of bondbetween the carbon atoms and between the carbon and hydrogen atoms. Suggest why Dewar benzene and Ladenburg benzene are unstable isomers of C6H6. Complete Table 6.2 to predict the number of peaks in the proton (1H) NMR spectrum for Dewar benzene, Ladenburg benzene and delocalised benzene. Table 6.2 number of peaks Dewar benzene Ladenburg benzene delocalised benzene The reaction of phenylethanone with 1,4-dibromobutane, BrCH2CH2CH2CH2Br, in the presence of FeBr3 is shown in . O O BrCH2CH2CH2CH2Br phenylethanone FeBr3 + Br + HBr The mechanism of this reaction is similar to that of the alkylation of benzene. Construct an equation for the formation of the electrophile, BrCH2CH2CH2CH2 +. Complete the mechanism in for the reaction of phenylethanone with BrCH2CH2CH2CH2 + ions. Include all relevant curly arrows and charges. Draw the structure of the organic intermediate. O O BrCH2CH2CH2CH2 organic intermediate + Br + The reaction shown in forms small amounts of two by-products, Y (C20H22O2) and Z (C12H14O). Suggest structures for Y and Z in the boxes in . Y (C20H22O2) Z (C12H14O)
9701_s24_qp_41
THEORY
2024
Paper 4, Variant 1
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State what is meant by partition coefficient, Kpc. The partition coefficient, Kpc, for a compound, X, between carbon disulfide, CS2, and water is 10.5. 1.85 g of X is dissolved in water and made up to 100.0 cm3 in a volumetric flask. 40.0 cm3 of this aqueous solution is shaken with 25.0 cm3 of CS2. The mixture is left to reach equilibrium. Calculate the mass of X, in g, extracted into the CS2 layer. mass of X = g The compound C6H6 has many structural isomers. Four suggested structures of C6H6 are shown in . delocalised benzene Kekulé benzene Dewar benzene Ladenburg benzene Using , complete Table 6.1 to predict the number of carbon atoms that have sp, sp2 and sp3 hybridisation in Kekulé benzene, Dewar benzene and Ladenburg benzene. Table 6.1 C6H6 structure sp hybridised sp2 hybridised sp3 hybridised Kekulé benzene Dewar benzene Ladenburg benzene Describe the shape of delocalised benzene. Include the geometry of each carbon, the C-C-H bond angle and the type of bondbetween the carbon atoms and between the carbon and hydrogen atoms. Suggest why Dewar benzene and Ladenburg benzene are unstable isomers of C6H6. Complete Table 6.2 to predict the number of peaks in the proton (1H) NMR spectrum for Dewar benzene, Ladenburg benzene and delocalised benzene. Table 6.2 number of peaks Dewar benzene Ladenburg benzene delocalised benzene The reaction of phenylethanone with 1,4-dibromobutane, BrCH2CH2CH2CH2Br, in the presence of FeBr3 is shown in . O O BrCH2CH2CH2CH2Br phenylethanone FeBr3 + Br + HBr The mechanism of this reaction is similar to that of the alkylation of benzene. Construct an equation for the formation of the electrophile, BrCH2CH2CH2CH2 +. Complete the mechanism in for the reaction of phenylethanone with BrCH2CH2CH2CH2 + ions. Include all relevant curly arrows and charges. Draw the structure of the organic intermediate. O O BrCH2CH2CH2CH2 organic intermediate + Br + The reaction shown in forms small amounts of two by-products, Y (C20H22O2) and Z (C12H14O). Suggest structures for Y and Z in the boxes in . Y (C20H22O2) Z (C12H14O)
9701_s24_qp_43
THEORY
2024
Paper 4, Variant 3
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DNA carries the genetic code in living organisms and consists of a double helix. Describe what is meant by a double helix. How are the strands of the double helix held together? In replicating the genetic code two RNA molecules, mRNA and tRNA, are used to perform functions called transcription and translation. Describe the role of the RNA molecules in these two functions. transcription translation When an egg is boiled, the protein changes from a viscous liquid to a solid. Suggest what causes this change as the protein is heated. Why is there no change to the primary structure of the protein under these conditions? Examiner’s Use Describe in outline how energy is provided in animal cells.
9701_w07_qp_4
THEORY
2007
Paper 4, Variant 0
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Questions Discovered
313