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Alkenes: Reactions with carbenes (McM 7.6) cont.

Alkenes: Reactions with carbenes (McM 7.6) cont. Alkenes: Addition of radicals etc - Polymerisation (McM 7.10, 14.7) Alkenes: Formation by elimination reactions (McM 11.12, 11.13) Substitution reactions: Cleavage of ethers (McM 18.5) Organometallic coupling react. (McM 10.9, lab ex 10).

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Alkenes: Reactions with carbenes (McM 7.6) cont.

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  1. Alkenes: Reactions with carbenes (McM 7.6) cont. Alkenes: Addition of radicals etc - Polymerisation (McM 7.10, 14.7) Alkenes: Formation by elimination reactions (McM 11.12, 11.13) Substitution reactions: Cleavage of ethers (McM 18.5) Organometallic coupling react. (McM 10.9, lab ex 10)

  2. Polymerization of dienes (McM 14.7) Natural and synthetic rubber • Radical polymerization • Cationic polymerization Acid cat polymerization of 1,3-butadiene 1,4-addition

  3. Hevea brasiliensis, tropical Americas. Cautchuc resin from the Isonandra Gutta tree (South east Asia) Less elastic than nat. rubber Isolation under-water cables Little use today

  4. Elimination reactions - Repetition • One step • 2. order • Stereospecific • Two steps • 1. order • 1. step rate limiting • 1.step = 1. step in SN1 • Not stereospecific Elimination in competition with substitution

  5. E2 and stereochemistry Large subst in e pos. favored

  6. Deuterium Isotope Effect (McM 11.14) (Kinetic Isotope Effect) • Important in elucidation of reaction mechanisms • Cleavage of C-H and C-D requires different amount of energy Hookes Law, Stretching frequencies, IR Relationship between Streching frequency (n) and zero-point energy (E0) E0 = 1/2 hn E0C-H 18 kJ/mol E0C-D 13 kJ/mol Higher activation energy for cleavage of C-D Cleavage of C-H will be faster TS#

  7. Substitution reactions - Repetition • One step • 2. order • Stereospecific - Inversion • Sterical hindrance • Two steps • 1. order • 1. step rate limiting • 1.step = 1. step in E1 • Not stereospecific - Racimisation • Stabilisation of carbocation X: Leaving group, Godd leaving group - weak base

  8. C-C Bond Formation - Organometallic Coupling Reactions (McM 10.9, Lab ex 10)

  9. Grignard reagents and Organolithium reagents Reacts with carbonyls Strong bases RMgX or RLi does not react well with alkyl halides in substitutions

  10. Organocuprates (McM 10.9) Gilman reagent Dialkylcuprate (R: alkyl, alkenyl, alkynyl, aryl) Participate in substitution with alkylhalides (Cl, Br, I) Also reaction with alkenyl halides and arylhalides (sp2) Not SN1 or SN2

  11. Palladium catalyzed coupling reactions (Lab ex. 10) Alkenyl or aryl halides Pd complex from aklyl halides unstable Met: -ZnX, -B(OH)2, -SnR3 (-MgX) Alkynyl, alkenyl, aryl, alkyl reacts (depending on the metal used)

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