Edexcel Jun 2009 Paper 2 Q20 (with explained solutions) |

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Edexcel Jun 2009 Paper 2 Q20

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PMT SECTION B Answer ALL the questions. Write your answers in the spaces provided. 20 When 2-chloro-2-methylpropane is heated in a mixture of water and ethanol at 65 C, two types of reaction occur. A mixture of two organic products, 2-methylpropan-2-ol and 2-methylpropene, is formed. CH3 H Cl Reaction 1 Reaction 2 CH3 H OH CH3 C C (a) (i) Name the two reaction types that are taking place. (2) Reaction 1Reaction 2*(ii) Explain how the two products form, by describing the role of the water in each case. (4) Reaction 1Reaction 2*h34472A01124* 11 Turn over<br />
PMT (b) A proposed mechanism for Reaction 1 involved the formation of the carbocation, CH3 H3C C+ CH3 (i) What type of bond breaking must have occurred during the carbocation formation? (1)(ii) Suggest why 1-chlorobutane reacts with water via a different mechanism. (2)(c) Another halogenoalkane, 2-chlorobutane, behaves in a similar way to 2-chloro-2-methylpropane but in Reaction 2 can form three different alkenes. Suggest how three different alkenes can form and give their displayed formulae. (4)12 *h34472A01224*<br />
PMT (d) Suggest why 2-fluoro-2-methylpropane would react more slowly than 2-chloro-2-methylpropane in Reaction 1. What reagent could you use instead of water to increase the rate of this reaction involving 2-fluoro-2-methylpropane? Explain why the reagent would have this effect. (3)(Total for Question 20 = 16 marks) *h34472A01324* 13 Turn over<br />

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Mark Mark Removes a H atom Correct Answer Reaction 1(nucleophilic) substitution (1) Reaction 2elimination (1) Reject Correct Answer Reject Reaction 1 - Water can behave as a nucleophile /water can donate a lone pair (from oxygen)/water has a lone pair/water forms an OH ion (1) And attack (positive) carbon (originally attached to Cl)/bonds to the carbon/bonds to the carbocation (1) Reaction 2 - behaves as a base (1) and accepts a hydrogen ion/proton / donates e pair to H/removes a proton/removes a hydrogen ion/removes a H+ (1) In each case a correctly drawn mechanism could get (2) Correct Answer Heterolytic (fission) Notes Accept phonetic/incorrect spelling as long as the word is recognisable Reject Mark Section B Question Number 20 (a)(i) Question Number 20 (a)(ii) QWC Question Number 20 (b)(i)<br />
Mark Correct Answer Reject Negative inductive effect Butyl group less electron releasing/butyl group has less of a (positive) inductive effect (1) so less stable (positive charge on) carbocation (1) 0R 1- chlorobutane is a primary halogenoalkane/the carbon only has 1 other C attached (1) So forms a less stable carbocation (1) 0R Primary carbocation is less stable than a tertiary carbocation (2) 0R Water/OH can attack C on 1 chloroalkane more easily (so no need to form cation) OWTTE / 1 chloroalkane reacts via SN2 mechanism/CO bond forms before CCl breaks (1) As the carbon attacked is not surrounded by bulky groups OWTTE (1) Question Number 20 (b)(ii)<br />
Question Number 20 (c) Reject Mark Correct Answer Hydrogen (ion) can be eliminated from C on either side (of C attached to Cl)/double bond can form between 1st and 2nd or 2nd and 3rd carbon OWTTE (1) OR double bond cant rotate (so methyl group and hydrogens can be fixed in position) to form E and Z isomers / geometric isomers/cis and trans/stereoisomers/or named in diagrams OWTTE (1) allow descriptions in terms of cis and trans H C H C C H H (1) (1) H H CC (1) Methyl and ethyl groups do not need to be fully displayed Structural formulae/skeletal formulae For all 3 (2) For 2 (1) For 1 (0) For an incorrect haloalkane structure that can form 3 isomers including cis/trans (2 max) (eg 2-chloropentane)<br />
Question Number 20 (d) Question Number 21 (a)(i) Question Number 21 (a)(ii) Mark Mark Mark Reject Alkali Hydroxide Correct Answer (Slower) as CF bond is stronger (than C-Cl)/fluorine bonds more strongly/fluorine holds the carbon more strongly OR Slower as F is a poorer leaving group (than Cl) (1) Use sodium hydroxide /NaOH/ potassium hydroxide /KOH/ hydroxide ions (1) As OH is a stronger nucleophile / OH has a full negative charge/ more strongly attracted to C+ /OH has more lone pairs (than water)/ OH is more negative than water (1) Correct Answer Reject Hydrogen bonding Hydrogen bond(s) H bonding H bond(s) Notes Accept phonetic/incorrect spelling as long as the word is recognisable Not hydrogen on its own Dipole-dipole bond Permanent dipole-dipole bond Covalent bond van der Waals (forces) Temporary dipole-dipole Induced dipole-dipole London forces Any correct answer in conjunction with an incorrect response, eg hydrogen dipole- dipole bond. Reject Correct Answer (Fluorine atom) is more electronegative (1) Because it has less shielding / (bonding) electrons closer to the nucleus/ smaller /has less shells (so greater pull from nucleus on bonding electrons) (1) so HF has a (greater) dipole moment/H+ on HF (greater than on HBr)/HF is (more) polar (1)<br />

Question 20 21 22 23

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