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Carey Chapter 3 – Conformations of Alkanes and Cycloalkanes

This chapter explores the different conformations of alkanes and cycloalkanes, including their structures and stability. It also covers the analysis of monosubstituted and disubstituted cycloalkanes.

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Carey Chapter 3 – Conformations of Alkanes and Cycloalkanes

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  1. Carey Chapter 3 – Conformations of Alkanes and Cycloalkanes Figure 3.5

  2. Conformational Analysis Cytosine (C) (from TGCA alphabet in DNA Hemoglobin

  3. Thymidine – incorporated into DNA as “T” Zidovudine (AZT) – incorporated into DNA instead of T – stops chain growth

  4. 3.1 Conformational analysis of Ethane Since single bonds can rotate around the bond axis, different conformations are possible -conformational analysis Figure 3.1 (use SpartanModel)

  5. 3.1 Conformational analysis Different 3-D depictions of Ethane Newman Projection Wedge/dash Sawhorse Rotation aroundthe central C-C bond will cause the hydrogens to interact -rotamers or conformers

  6. Definitions Gauche torsion angle 60o Eclipsed torsion angle 0o Anti torsion angle 180o Both gauche and anti conformers arestaggered Eclipsed conformers are destabilized bytorsional strain

  7. 3.1 Conformational analysis of Ethane Figure 3.4

  8. 3.2 Conformational analysis of Butane Figure 3.7

  9. 3.3 Conformations of higher alkanes eclipsed eclipsed Anti (staggered) Gauche (staggered) Applicable for any acyclic molecule

  10. 3.4 Cycloalkanes – not planar Cyclohexane

  11. 3.5 Cyclopropane and Cyclobutane Figure 3.10

  12. 3.6 Cyclopentane Figure 3.12

  13. 3.7 Conformations of Cyclohexane Conformationally flexible (without breaking bonds) Chair Boat Chair

  14. 3.7-3.8 Cyclohexane – axial and equatorial positions Figure 3.13-3.14

  15. 3.9 Conformational inversion – ring flipping Figure 3.18

  16. 3.10 Analysis of monosubstituted cyclohexanes Based on unfavourable1,3-diaxialinteractions

  17. 3.11 Disubstituted cycloalkanes - Stereoisomers Cis-1,2-dimethylcyclopropane is less stable than the trans isomer Cis-1,2-dimethylcyclohexane is less stable than the trans isomer Cis-1,3-dimethylcyclohexane is more stable than the trans isomer Cis-1,4-dimethylcyclohexane is less stable than the trans isomer All based on interactions between substituents and other groups on the ring

  18. 3.11 Disubstituted Cyclopropanes Figure 3.20

  19. 3.12 Disubstituted Cyclohexanes Consider 1,2- ; 1,3- ; and 1,4-disubstituted isomers trans-1,2-dimethylcyclohexane is morestable than the cis isomer cis-1,3-dimethylcyclohexane is more stable than the trans isomer trans-1,4-dimethylcyclohexane is more stable than the cis isomer

  20. 3.13 Medium and large rings – not covered 3.14 – Polycyclic compounds – covering bicyclics Bicyclobutane Bicyclo[3.2.0]heptane Bicyclo[2.2.2]octane

  21. 3.15 Heterocyclic compounds tetrahydrofuran pyrrolidine piperidine morphine ritilin librium

  22. 3.15 Heterocyclic compounds D-Glucose (dextrose, blood sugar)

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