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Hydrocarbons from Petroleum

4. NOMENCLATURE AND CONFORMATIONS OF ALKANES AND CYCLOALKANES. (approx. lecture time: 4 hr ) Topics covered: 4.1-4.17. Hydrocarbons from Petroleum. The Unbranched Alkanes. Nomenclature. 1 o (primary) hydrogens also known as methyl hydrogens

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Hydrocarbons from Petroleum

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  1. 4. NOMENCLATURE AND CONFORMATIONS OF ALKANES AND CYCLOALKANES. (approx. lecture time: 4 hr) Topics covered: 4.1-4.17. Hydrocarbons from Petroleum

  2. The Unbranched Alkanes

  3. Nomenclature

  4. 1o (primary) hydrogens also known as methylhydrogens 2o (secondary) hydrogens also known as methylenehydrogens 3o (tertiary) hydrogens also known as methinehydrogens (Hydrogens on CH4 or NH4+ are called quaternaryhydrogens)

  5. Simplified IUPAC Nomenclature Rules • Locate longest alkyl chain. The length of this chain determines the parent name. • If there are chains of equal length, choose the one with larger number of substituents (avoids complex substituents) • Number the chain beginning at end closer to the first substituent. If there is a tie, begin numbering at the end closer to the second substituent. • Substituent names are placed in alphabetical order (ignore prefixes such as di, tri, tetra, sec & tert, etc. BUT NOT cyclo and iso). • The final name has no spaces between words. Commas and hyphens are used between “words”.

  6. Alkyl Halides and Alcohols

  7. Cycloalkanes (lower set of numbers in 1,2,4 vs 1,3,4) (lower set of numbers in 1,3 vs 1,5)

  8. (Here, the alcohol takes precedence and numbering starts there)

  9. Bicyclic Compounds Start numbering at the bridgehead and go around the longest bridge first

  10. Alkenes

  11. For simple cyclic alkenes (no alcohol function), the alkene must be contained in the numbers “1,2” The presence of the alcohol takes precedence. Start numbering here.

  12. Alkynes and Enynes Numbering enynes(ene and yne): start from the end closer to the first multiple bond. If there is a tie, give the alkene the lower number

  13. Conformational Analysis of Ethane

  14. Energy Diagram for C-C Bond Rotation

  15. Conformational Analysis of Butane

  16. Energy Diagram for C-C Bond Rotation

  17. Strain Energies InteractionCause Energy Eclipsing H Torsional strain 4.0 kJ/mol Eclipsing H and CH3 Mostly torsional strain 6.0 Eclipsing CH3 Torsional and steric 11 Gauche CH3 Steric 4 Torsional strain: due to unfavourable“eclipsing” orbital interactions Steric strain: due to “crowding” of atomic nuclei

  18. The Zig-Zag Structure of Linear Alkanes Why do we draw alkanes in a zig-zag manner?

  19. What’s in common in these compounds? cyclohexane Dodecahedrane Diamond (Hint: JRR Tolkien's first book of his famous trilogy)

  20. Lord of the Rings Cyclohexane,the true Lord of the Rings (in organic chemistry; mastering it will give you great power indeed!) Lord of the Rings in Middle Earth. The bearer has immense power, but it’s all fantasy.

  21. The Cycloalkanes [109o is the perfect tetrahedral angle (sp3 hybrid)] Rings have angle strain, in addition to torsion and steric strains Angle Strain: due to expansion or compression of required bond angles. Torsional strain: due to unfavourable eclipsing interactions of bonding electrons. Steric strain: due to repulsive interactions of atoms in close proximity.

  22. The True Shapes of Cycloalkanes “flat” “bent” “envelope” “chair”

  23. Total Strain Energy vs Ring Size

  24. Conformational Analysis of Cyclohexane model from your molecular model set space filling model 4 1

  25. Chair and Boat Conformations boat chair (A high energy form) (lowest energy form)

  26. The Cyclohexane Ring Flip

  27. Energy Level Diagram for Cyclohexane Ring Flip (For information only. Do not memorize!)

  28. Conformational Analysis for Methylcyclohexane 1,3-diaxial interactions

  29. 1,3-Dixial Interactions are Gauche Interactions

  30. 1,4-Dimethyl Cyclohexanes

  31. 1,2-Dimethyl Cyclohexanes

  32. Importance of 3-D Structures Controlling and understanding the 3-D shapes of organic molecules are essential for designing molecules that will function in desired ways. Chemical information is “stored” and “transferred” by the 3-D shapes of organic molecules.

  33. The Decalins “flexible” “rigid” (more stable)

  34. Synthesis of Alkanes: Hydrogenation of Alkenes and Alkynes

  35. The Importance of Rings (The Steriods) Corticosteroids: metabolism & immune function Anabolic Steroids: muscle & bone growth Sex Steroids: human reproduction Cholesterolis a waxy steroid found in the cell membranes. It is an essential component of mammalian cell membranes.

  36. An Infinite Array of Cyclohexane Rings (minus the hydrogens) Diamond

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