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Electrophilic Reactions

Electrophilic Reactions. Electrophilic Reactions. Alkenes + Alkynes Unsaturated hydrocarbon : contains one or more carbon-carbon double or triple bonds alkene : contains a carbon-carbon double bond and has the general formula C n H 2n

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Electrophilic Reactions

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  1. Electrophilic Reactions

  2. Electrophilic Reactions

  3. Alkenes + Alkynes • Unsaturated hydrocarbon:contains one or more carbon-carbon double or triple bonds • alkene:contains a carbon-carbon double bond and has the general formula CnH2n • - alkyne:contains a carbon-carbon triple bond and has the general formula CnH2n-2 Electrophilic ReactionsAddition to unsaturated carbon

  4. Alkenes Electrophilic ReactionsAddition to unsaturated carbon • IUPAC Nomenclature • use the infix -en- to show the presence of a carbon-carbon double bond • number the parent chain to give the 1st carbon of the double bond the lower number • follow IUPAC rules for numbering and naming substituents • for a cycloalkene, the double bond must be numbered 1,2

  5. Alkenes Electrophilic ReactionsAddition to unsaturated carbon Some alkenes, particularly low-molecular-weight ones, are known almost exclusively by their common names

  6. Electrophilic ReactionsAddition to unsaturated carbon Alkenes The cis,trans system:configuration is determined by the orientation of atoms of the main chain

  7. Electrophilic ReactionsAddition to unsaturated carbon Alkenes • Configuration: E,Z • Assign a priority to the substituents on each carbon of the double bond • if the groups of higher priority are on the same side of the double bond, the configuration is Z (German: zusammen, together) • if the groups of higher priority are on opposite sides of the double bond, the configuration is E (German: entgegen, opposite)

  8. Electrophilic ReactionsAddition to unsaturated carbon Alkenes – E,Z configuration • Priority rules • Priority is based on atomic number; the higher the atomic number, the higher the priority • 2. If priority cannot be assigned on the basis of the atoms bonded directly to the double bond, look to the next set of atoms; priority is assigned at the first point of difference • 3. Atoms participating in a double or triple bond are considered to be bonded to an equivalent number of similar atoms by single bonds

  9. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of hydrogen halides Alkenes –Addition of water

  10. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of hydrogen halides to double bonds with substituted carbons Carbocations are planar -> attack from both sides possible!!

  11. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of hydrogen halides to double bonds with substituted carbons -> Addition is regioselective (regioselective reaction:a reaction in which one direction of bond-forming or bond-breaking occurs in preference to all other directions) Markovnikov’s rule: in additions of HX, H adds to the carbon with the greater number of hydrogens

  12. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of hydrogen halides to double bonds with substituted carbons -> Carbocation rearrangements

  13. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of halogens

  14. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of halogens -> Stereochemical consequences of electrophil addition -> gives 2,3 dibromobutane as a pair of enantiomers, R,R and S,S -> a result of anti addition

  15. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of halogens -> Stereochemical consequences of electrophil addition -> gives 2,3 dibromobutane as a meso R,S isomer

  16. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of halogens -> Stereochemical consequences of electrophil addition -> gives 1,2 dibromocyclohexan as a pair of enantiomers, R,R and S,S -> a result of anti addition

  17. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of halogens -> Stereochemical consequences of electrophil addition

  18. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of halogens in water -> Halo alcohol (halohydrin) Halo alcohols can be used to make -> epoxides

  19. Electrophilic ReactionsAddition to unsaturated carbon Alkenes –Addition of halogens in water under basic conditions -> Epoxides

  20. Electrophilic ReactionsAddition to unsaturated carbon • Alkynes • IUPAC nomenclature • use the infix -yn- to show the presence of a carbon-carbon triple bond • number the parent chain to give the 1st carbon of the triple bond the lower number • follow IUPAC rules for numbering and naming substituents

  21. Electrophilic ReactionsAddition to unsaturated carbon Alkynes –Addition of halides

  22. Electrophilic ReactionsAddition to unsaturated carbon Alkynes –Addition of halides

  23. Electrophilic ReactionsAddition to unsaturated carbon Alkynes – Hydration gives a keton

  24. Electrophilic ReactionsAddition to conjugated systems • Alkenes – conjugated systems • Dienes, trienes, and polyenes • for an alkene with n carbon-carbon double bonds, each of which can show cis-trans isomerism, 2ncis-trans isomers are possible • consider 2,4-heptadiene; it has four cis-trans isomers, two of which are drawn here

  25. Electrophilic ReactionsAddition to conjugated systems Alkenes – conjugated systems • vitamin A has five double bonds • vitamin A is the all-trans isomer

  26. Electrophilic ReactionsAddition to conjugated systems Alkenes – addition of halides

  27. Electrophilic ReactionsAddition to conjugated systems Alkenes – addition of halides Conjugate addition

  28. Electrophilic ReactionsAddition to conjugated systems Alkenes – addition of halogens

  29. Electrophilic ReactionsCarbocations as electrophiles Cationic polymerization Polystyrene

  30. Electrophilic ReactionsCarbocations as electrophiles Cationic polymerization – intramolecular electrophilic addition

  31. Electrophilic ReactionsCarbocations as electrophiles Cationic polymerization – intramolecular electrophilic addition Terpenoids and Steroids Huge group of natural products -> flavouring, aromatherapy oils, vitamins (A, K), steroid hormons (lanosterol, cholesterol) Terpene:a compound whose carbon skeleton can be divided into two or more units identical with the carbon skeleton of isoprene

  32. Electrophilic ReactionsCarbocations as electrophiles Cationic polymerization – intramolecular electrophilic addition • myrcene, C10H16, a component of bayberry wax and oils of bay and verbena • menthol, from peppermint • Vitamin A Terpenoids and Steroids

  33. Electrophilic ReactionsCarbocations as electrophiles Cationic polymerization – intramolecular electrophilic addition Terpenoids and Steroids Lemon oil Pine oil Eucalyptus oil

  34. Catalytic hydration -> NOT a radical reaction (Chapter 9: Radical reactions) Involvement of atomic hydrogen -> mechanism has more in common with radical reaction than with ionic reaction Catalytic HydrationAddition of hydrogen to alkenes and alkynes

  35. Catalytic HydrationAddition of hydrogen to alkenes and alkynes

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