Edexcel Jan 2013 Paper 5 Q17 (with explained solutions) |

Skip to content

Edexcel Jan 2013 Paper 5 Q17

Answers available below

SECTION C Answer ALL the questions. Write your answers in the spaces provided. 17 Tranexamic acid Tranexamic acid is an amino acid. It is a white crystalline solid which melts at 300 C. It is used to reduce bleeding during surgery and dental procedures and is especially useful where patients suffer from deficiencies in blood-clotting factors. The structure of tranexamic acid can be drawn as shown below. H2N CH2 CH2CH2 C CH2CH2 OH or COOH H2N As the name suggests, tranexamic acid is the trans form of a compound that forms geometric (or cis-trans or E-Z) isomers. (a) (i) Explain why some molecules which contain a C C double bond show geometric isomerism. (2)(ii) Suggest how tranexamic acid can form geometric isomers although it does not have a C C double bond. (1)20 *P41215A02024*<br />
(iii) Complete the diagram to show the structure of the cis isomer. CH2CH2 C CH2CH2 (iv) Explain why tranexamic acid melts at 300 C while the alkane, undecane (C11H24) which has almost the same number of electrons, melts at 26 C. A detailed description of the forces involved is not required. (1) (3)(b) The diagram below shows a compound, K, which is a derivative of tranexamic acid. C Cl H2N (i) Identify by name or formula a compound that might react with tranexamic acid to form K. (1)*P41215A02124* 21 Turn over<br />
(ii) Under suitable conditions, molecules of K react together forming a polymer, L. Draw the structure of L, showing two repeat units. (2) (iii) Name the type of polymerization that results in the formation of L.(iv) State the type of naturally occurring substance which contains the same type of linkage as in the polymer L. (1) (1)22 *P41215A02224*<br />
(c) If the sequence of reactions, that produces polymer L from tranexamic acid, is carried out starting with the cis isomer of tranexamic acid, an organic compound, M, is formed. The low resolution nuclear magnetic resonance (nmr) spectrum of M has six peaks with relative heights 4:4:2:1:1:1. The infrared (IR) spectrum of M has peaks in the region 17001630 cm1 and 35003140 cm1. (i) The structure of M is shown below. The nmr spectrum shows that the molecule, M, has six different hydrogen environments. Use the letters a to f to label the H atoms of M showing the six hydrogen environments. All thirteen hydrogen atoms should be labelled. H2C HC C H2 H2C HC CH2 CH2 (ii) Explain how the IR data are consistent with the structure of M. (4) (2)(iii) Suggest why M is formed from the cis isomer but not from the trans isomer. (2)(Total for Question 17 = 20 marks) TOTAL FOR SECTION C = 20 MARKS TOTAL FOR PAPER = 90 MARKS *P41215A02324* 23<br />

Show answer

Section C Question Number 17(a)(i) Acceptable Answers Reject Mark There is a barrier to rotation about a (C=C) bond (1) ALLOW restricted / limited / no rotation Each carbon atom (in the C=C double bond) has (two) different atoms / groups attached (1) IGNORE reference to priority groups Just molecule cannot rotate Question Number 17(a)(ii) There is a barrier to / restricted rotation about Acceptable Answers the ring OR The ring behaves like a double bond Question Number 17(a)(iii) Acceptable Answers Mark Mark Reject Reference to benzene ring Just molecule cannot rotate Reject Omission of amine CH2 Any diagram of the correct molecule showing the groups (attached to the ring) on same side of the ring OR zwitterion ALLOW Amine group in skeletal form<br />
Question Number 17(a)(iv) Tranexamic acid exists as a zwitterion Acceptable Answers Reject Mark OR Diagram of zwitterion OR Description of zwitterion formation (1) So the (strongest) intermolecular forces are ionic (strong) ALLOW electrostatic for ionic (1) IGNORE H bonding in tranexamic acid if either of the first two marks scored. Otherwise Hydrogen bonding in tranexamic acid scores 1/2 max Undecane has (only) (much weaker) London / dispersion / van der Waals / temporary induced dipole (-induced dipole) forces / interactions (1) Reject Mark HCl Reject Mark Question Number 17(b)(i) Question Number 17(b)(ii) Acceptable Answers Phosphorus(v) chloride / PCl5 ALLOW phosphorus pentachloride / phosphorus(III) chloride / PCl3 / phosphorus trichloride Thionyl chloride (sulfur dichloride oxide) / SOCl2 Acceptable Answers C H2 C H2 First mark amide linkage ALLOW CONH for amide linkage (1) Second mark Completion of structure (brackets not required) with displayed or skeletal formula (1) Second mark dependent on first Dimer scores amide linkage mark only<br />
Question Number 17(b)(iii) Condensation / addition-elimination Acceptable Answers (polymerization) Question Number 17(b)(iv) Protein / proteins / polypeptide / polypeptides / Acceptable Answers peptide / peptides ALLOW Enzyme / Enzymes Question Number 17(c)(i) Check sequence of letters. Candidates may have Acceptable Answers Reject Addition (polymerization) Elimination (polymerization) Polyamide formation Reject Nylon Polyamide amino acids Mark Mark Reject Mark labelled the groups of hydrogen atoms with different letters, which is fine. First mark Unique NH (at e) (1) Second mark (1) Unique CH2 (at c) Third mark (1) CH (at d) and CH (at f) with different unique labels Fourth mark 2CH2 (at a) and 2CH2 (at b) with different new labels (1) H2C HC CH2 C H2 CH2 HC H2C<br />
Question Number 17(c)(ii) CO amide (stretching vibrations are in the region) Acceptable Answers 1700-1630 cm1 (1) NH amide (stretching vibrations are in the region) 3500-3140 cm1 (1) Amide only needs to be mentioned once but These answers without mention of amide max 1 Amides have peaks in these regions max 1 Reject Mark Ketone Amine (for amide) Reject Mark bond Question Number 17(c)(iii) Any two from Acceptable Answers In the trans isomer the (amine and acid chloride) groups are too far apart to react intramolecularly / to form M OR Because the groups are on opposite sides of the (plane of the) ring OR More likely to polymerize / react with adjacent molecules. (2) Marks may also be scored by a reverse argument: In the cis isomer the (amine and acid chloride) groups are on the same side of the (plane of the) ring (1) So close enough to react intramolecularly / to form M (1) Total for Q17 = 20 Marks TOTAL FOR SECTION C = 20 MARKS<br />

Question 14 15 16 17

About us | Need Help? | Feedback

Proudly powered by WordPress | Theme: Sydney by aThemes.