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IUPAC Nomenclature of Dienes

IUPAC Nomenclature of Dienes. Find the longest chain containing both double bonds. 1. 2. 3. 4. 5. 3-butyl-1,4-pentadiene. IUPAC Nomenclature of Dienes. Use corresponding alkane name but replace the “ ne” ending with “ diene”. 3-butyl-1,4-pentadiene. “pentane” changed to “pentadiene”.

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IUPAC Nomenclature of Dienes

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  1. IUPAC Nomenclature of Dienes • Find the longest chain containing both double bonds 1 2 3 4 5 3-butyl-1,4-pentadiene Chapter 7

  2. IUPAC Nomenclature of Dienes • Use corresponding alkane name but replace the “ne” ending with “diene” 3-butyl-1,4-pentadiene “pentane” changed to “pentadiene” Chapter 7

  3. IUPAC Nomenclature of Dienes • Number in the direction that gives the lowest number to a double bond 1,5-heptadiene not 2,6-heptadiene Chapter 7

  4. IUPAC Nomenclature of Dienes • List substituents in alphabetical order 5-ethyl-2-methyl-2,4-heptadiene Chapter 7

  5. IUPAC Nomenclature of Dienes • Place numbers indicating the double bond positions either in front of the parent compound or in the middle of the name immediately before the diene suffix 5-ethyl-2-methyl-2,4-heptadiene or 5-ethyl-2-methyl-hepta-2,4,-diene Chapter 7

  6. IUPAC Nomenclature of Dienes Chapter 7

  7. Configurational Isomers of Dienes Chapter 7

  8. Types of Dienes • When double bonds are separated by at least one sp3carbon, isolated diene Chapter 7

  9. Types of Dienes • When double bonds are separated by only one single bond (i.e. four sp2 carbons in a row), conjugated diene Chapter 7

  10. Types of Dienes • When both sets of double bonds emanate from the same carbon, cumulated diene Chapter 7

  11. Relative Stabilities of Dienes • Conjugated dienes are more stable than isolated dienes because • An sp2-sp2 single bond is shorter and stronger than a sp3-sp2 single bond • Resonance also stabilizes the conjugated diene Chapter 7

  12. Relative Stabilities of Dienes • Doubly-bonded carbons in isolated and conjugated dienes all are sp2hybridized • The central carbon in a cumulated diene is sp hybridized Chapter 7

  13. Relative Stabilities of Dienes • The heat of hydrogenation of allene is similar to that of 1-butyne; both have at least one sp carbon • Additional reactivity of cumulated dienes will not be considered in this course Ho = -70.5 kcal/mol Ho = -69.9 kcal/mol Chapter 7

  14. Reactivity Considerations • Dienes, like alkenes and alkynes, are nucleophilic - they have  electrons to contribute to bonding Chapter 7

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