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Dubai

Optical Isomerism - A Level Chemistry

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Published in: Chemistry
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Chirality, Optical isomerism, Recimic mixture for A levels - (EdExcel, AQA and CAIE)

Muhammed S / Abu Dhabi

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Qualification: Post Graduate in Chemistry

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  1. 4-cn-e.-o S Optical isomers - are compounds they rotates the plane of plane polarised light either in clockwise direction or in anticlockwise direction first Polaroid sheet monochromatic polariser fig B Polarisation of light. plane polarised light second Polaroid sheet at right angles no light passes through viewer analyser sample polariser light source A figc You can see how the plane of polarisation of the polarised light is rotated anticlockwise as it passes through the sample tube. The compounds rotates the plane of plane polarized light is known as optically active compounds
  2. Conditions to become chiral or optically active :
  3. When mixed in equimolar quantities, Which pair Of molecules Will not rotate the plane Of plane-polarised light? •Avon — 2 Which Of these molecules can rotate the plane of plane-polarised light? O A H2NCH2COOH C] B HOCH2CH2COOH (Total for Question 2 = 1 mark) 17 This question is about carboxylic acids and their derivatives. (a) Lactic acid, , is produced in muscles as a result Of anaerobic respiration. The structure of lactic acid is COOH HO Give a reason why lactic acid shows optical isomerism. (ii) A laboratory sample of lactic acid does not rotate the plane of plane-polarised monochromatic light. Give a reason for this observation.
  4. (iii) Give the structure of the organic product formed when lactic acid reacts with concentrated phosphoric(V) acid, HYPO,. OH 8 The compound menthol has the Structure shown. Some of the carbon atoms are labelled P, Q R and S. men thol OH (a) What is the number of chiral centres in a molecule of menthol?
  5. 13 How many optical isomers does this molecule have? 14 Which ofthese structures is not identiål to the others? OH (Total for OH stion 13 = I mark) Structure D CH2CH, Structure A A Structure A B Structure B C Structure C D Structure D Structure B CH2CH, Structure C O (Total for Question 14 = 1 mark) TOTAL FOR SECTION A = 20 MARKS
  6. Q_A.R Recimic mixture : If the mixture contains equal amount of two enantiomers (dextro and leavo ) - ie the recimic mixture; the overall rotation of plane polarized light is zero,
  7. (e) 2-bromobutane can react with aqueous hydroxide ions by an SNI mechanism. Explain why the butan-2-ol produced from a single optical isomer of 2-bromobutane, using this mechanism, is not Optically active. (iii) When plane-polarised light is passed through an optical isomer, the plane of polarisation is A B C D diffracted -F reflected refracted rotated
  8. (c) The product of the hydrolysis of 2-bromobutane is butan-2-ol. Both molecules are Chira State what is meant by the term chiral, using three-dimensional diagrams Of the enantiomers Of butan-2-01 to illustrate your answer. (b) What is the classification of the dihalogenoalkane shown? C] C] A primary B secondary C tertiary D primary and secondary (Total for Question 3 = 5 marks)

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