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Alkenes and Alkynes Chapter #3

Alkenes and Alkynes Chapter #3. Alkene Introduction. Hydrocarbon with carbon-carbon double bonds Sometimes called olefins , “oil-forming gas” General formula C n H 2n n≥2 Examples n=2 C 2 H 4. Common Names. Usually used for small molecules. Examples:. CH 3.

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Alkenes and Alkynes Chapter #3

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  1. Alkenes and Alkynes Chapter #3

  2. Alkene Introduction • Hydrocarbon with carbon-carbon double bonds • Sometimes called olefins, “oil-forming gas” • General formula CnH2n n≥2 • Examples n=2 C2H4

  3. Common Names Usually used for small molecules. Examples: CH3 CH2=CH2CH2=CH-CH3CH2=C-CH3 ethylene propylene isobutylene Vinyl carbons are the carbons sharing a double bond in blue Vinylhydrogensare the hydrogens bonded to vinyl carbons in red

  4. IUPAC Nomenclature • Parent is longest chain containing the double or triple bond. • -ane changes to –ene (or -diene, -triene) for double bonds, or –yne (or –diyne, -triyne). • Number the chain so that the double bond, or triple bond has the lowest possible number. • In a ring, the double bond is assumed to be between carbon 1 and carbon 2.

  5. Name These Alkenes

  6. Name These Alkenes 1-butene

  7. Name These Alkenes 1-butene 2-methyl-2-butene

  8. Name These Alkenes 1-butene 2-methyl-2-butene 3-methylcyclopentene

  9. Name These Alkenes 1-butene 2-sec-butyl-1,3-cyclohexadiene 2-methyl-2-butene 3-methylcyclopentene

  10. Name These Alkenes 1-butene 2-sec-butyl-1,3-cyclohexadiene 2-methyl-2-butene 3-n-propyl-1-heptene 3-methylcyclopentene

  11. = CH2 - CH = CH2 - CH2 - CH = CH2 - CH2 - CH = CH2 allyl allyl methylene vinyl Alkene Substituents Name = ?

  12. = CH2 - CH = CH2 - CH2 - CH = CH2 - CH2 - CH = CH2 allyl allyl methylene vinyl Alkene Substituents Name = Methylenecyclohexane Name =

  13. = CH2 - CH = CH2 - CH2 - CH = CH2 allyl methylene vinyl Alkene Substituents Name = Methylenecyclohexane Name = vinylcyclohexane

  14. Alkyne Common Names • Acetylene is the common name for the two carbon alkyne. • To give common names to alkynes having more than two carbons, give alkyl names to the carbon groups attached to the vinyl carbons followed by acetylene.

  15. Alkyne Examples

  16. Alkyne Examples Isopropyl methyl acetylene

  17. Alkyne Examples Isopropyl methyl acetylene sec-butyl Cyclopropyl acetylene

  18. Cis-trans Isomerism • Similar groups on same side of double bond, alkene is cis. • Similar groups on opposite sides of double bond, alkene is trans. • Cycloalkenes are assumed to be cis. • Trans cycloalkenes are not stable unless the ring has at least 8 carbons.

  19. Name these:

  20. Name these: trans-2-pentene

  21. Name these: trans-2-pentene

  22. Name these: trans-2-pentene cis-1,2-dibromoethene

  23. Which of the following show cis/trans isomers?a. 1-pentene b. 2-pentene c. 1-chloro-1-pentene d. 2-chloro-1-pentene e. 2-chloro-2-pentene

  24. Solution to the Question

  25. Solution to the Question

  26. Which of the following show cis/trans isomers?a. 1-pentene-No b. 2-pentene- Yes c. 1-chloro-1-pentene- Yes d. 2-chloro-1-pentene- No e. 2-chloro-2-pentene- yes

  27. E-Z Nomenclature • Use the Cahn-Ingold-Prelog rules to assign priorities to groups attached to each carbon in the double bond. Highest priority is #1 and is the element with the largest atomic number. • If high priority groups are on the same side, the name is Z (for zusammen). • If high priority groups are on opposite sides, the name is E (for entgegen).

  28. 1 2 1 1 2 2 1 2 Example, E-Z 2Z 5E

  29. 1 2 1 1 2 2 1 2 Example, E-Z 2Z 5E 3,7-dichloro-(2Z, 5E)-2,5-octadiene

  30. Physical Properties • Low boiling points, increasing with mass. • Branched alkenes have lower boiling points. • Less dense than water. • Nonpolar (Hydrophobic)

  31. Alkene Synthesis Elimination Reactions: • Dehydrohalogenation (-HX) • Dehydration of alcohols (-H2O) Examples: Zaitsev’s rule: The major product contains the most substituted double bond

  32. Alkene Reactions I. Addition Reactions a. Hydration H O-H H+ C=C C-C Follows Markovnikov’s Rule + H-O-H Alcohol b. Hydrogenation H H Catalyst C=C C-C Catalyst = Ni, Pt, Pd + H-H Alkane c. Halogenation X X C-C C=C + X-X Dihalide X = Cl, Br, I

  33. Regiospecificity Markovnikov’s Rule: The proton (H+) of an acid adds to the carbon in the double bond that already has the most H’s. “Rich get richer.” H O-H Examples: H H H+ C-C H H C=C + H-O-H H CH3 H CH3 Major Products H Cl H H C-C C=C + H-Cl H H H CH3 H CH3

  34. Alkene Reactions (2) I. Addition Reactions (cont.) d. Hydrohalogenation H X Follows Markovnikov’s Rule C-C C=C + H-X Alkyl halide e. Glycol Formation H-O O-H C=C C-C + H-O-O-H Glycol

  35. Alkene Reactions Step 1: Pi electrons attack the electrophile. Step 2: Nucleophile attacks the carbocation

  36. Terpenes • Composed of 5-carbon isopentyl groups. • Isolated from plants’ essential oils. • C:H ratio of 5:8, or close to that. • Pleasant taste or fragrant aroma. • Examples: Myrcene (From bay or myrcia plants) α-Pinene (From pine trees) Β-Selinene (From celery) Menthol (From peppermint oil) Camphor (From evergreen trees) R-Carvone (From spearmint)

  37. Classification • Terpenes are classified by the number of carbons they contain, in groups of 10. • A monoterpene has 10 C’s, 2 isoprenes. • A diterpene has 20 C’s, 4 isoprenes. • A sesquiterpene has 15 C’s, 3 isoprenes.

  38. Terpenes head tail head head tail tail tail head head Geraniol (roses) Head to tail link of two isoprenes Called diterpene Menthol (pepermint) Head to tail link of two isoprenes another diterpene

  39. myrcene, from bay leaves Structure of Terpenes Two or more isoprene units, 2-methyl-1,3-butadiene with some modification of the double bonds.

  40. ALKENE REVIEW

  41. Describe the geometry around the carbon–carbon double bond. a. Tetrahedral b. Trigonal pyramidal c. Trigonal planar d. Bent e. Linear

  42. Answer a. Tetrahedral b. Trigonal pyramidal c. Trigonal planar d. Bent e. Linear

  43. Give the formula for an alkene. a. CnH2n-4 b. CnH2n-2 c. CnH2n d. CnH2n+2 e. CnH2n+4

  44. Answer a. CnH2n-4 b. CnH2n-2 c. CnH2n d. CnH2n+2 e. CnH2n+4

  45. Name CH3CH=CHCH=CH2. a. 2,4-butadiene b. 1,3-butadiene c. 2,4-pentadiene d. 1,3-pentadiene e. 1,4-pentadiene

  46. Answer a. 2,4-butadiene b. 1,3-butadiene c. 2,4-pentadiene d. 1,3-pentadiene e. 1,4-pentadiene

  47. Calculate the unsaturation number for C6H10BrCl. a. 0 b. 1 c. 2 d. 3

  48. Answer a. 0 b. 1 c. 2 d. 3 U = 0.5 [2(6) + 2 – (12)] = 1

  49. Name . a. Trans-2-pentene b. Cis-2-pentene c. Trans-3-methyl-2-pentene d. Cis-3-methyl-2-pentene

  50. Name a. Trans-2-pentene b. Cis-2-pentene c.Trans-3-methyl-2-pentene d. Cis-3-methyl-2-pentene

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