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CH264/3 Organic Chemistry II Cyclohexane Rings

CH264/3 Organic Chemistry II Cyclohexane Rings. Dr Andrew Marsh C515 a.marsh@warwick.ac.uk Dr David J Fox B510 d.j.fox@warwick.ac.uk. Today’s Lecture. 1. Cyclohexane conformation 2. Drawing cyclohexane chairs Monosubstituted cyclohexanes

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CH264/3 Organic Chemistry II Cyclohexane Rings

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  1. CH264/3 Organic Chemistry IICyclohexane Rings Dr Andrew Marsh C515 a.marsh@warwick.ac.uk Dr David J Fox B510 d.j.fox@warwick.ac.uk CH264

  2. Today’s Lecture • 1. Cyclohexane conformation • 2. Drawing cyclohexane chairs • Monosubstituted cyclohexanes • Disubstituted cyclohexanes, decalins and steroids CH264

  3. Angle strain in rings CH264

  4. Cyclohexane is ‘strain free’ A planar arrangement of the six methylene groups in cyclohexane does not give a tetrahedral shape for every carbon atom - this is achieved by puckering the ring. Cyclohexane does this by adopting mainly two conformations the CHAIR and the BOAT. CH264 CGW p.371

  5. Conformational analysis Nobel Prize 1969 CH264

  6. Cyclohexane is ‘strain free’ 109° angle allows near strain free cyclic molecule CH264

  7. Substituents on cyclohexane CGW p. 371 CH264

  8. Ring Flip CH264

  9. Chair Conformer CH264

  10. Boat Conformer CH264

  11. Substituted Cyclohexanes conc equatorial conformer K = >3000, >99.9% equatorial, >20 kJ mol-1 difference conc axial conformer CH264

  12. Substituted cyclohexanes: energy difference CGW p. 375 CH264

  13. Disubstituted cyclohexanes CH264

  14. The tert-butyl group is a conformational ‘lock’ CH264

  15. Decalins CGW p. 378

  16. Steroids: cholestanol Conformationally locked A–B–C–D rings CGW p. 379 CH264

  17. Outputs You should be able to: Draw cyclohexane as chair conformers (ii) Ring-flip monosubstituted cyclohexane (iii) Show which conformer is favoured in mono- and di-substituted cyclohexanes CH264

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