SORACHAI SAE-LIM SORACHAI SAE-LIM

Transcription

1 1 Alkenes

2 2 1.Dehydrohalogenation ของ alkyl halide ซ งเก ดปฏ ก ร ยาผ าน ซงเกดปฏกรยาผาน E2 ซ งปฏ ก ร ยาด งกล าวเก ดข นโดยใช เบส

3 3 Ex 1. H 3 C H C CH 3 C Br C 2 H 5 ONa / C 2 H 5 OH H CH 3 C 2 H 5 O CH 3 a) CH 3 CH C C H a) 2 H 5 OH Br - a) CH 3 H CH major product 2 b) b) CH 3 CH C Br b) CH 2 CH 3 CH 3 CH 2 C C 2 H 5 OH Br - CH 3 minor product

4 4 Geminal Trans Cis R R R R R H R H > > > R R R H R H H R > R H R H > R H H H > H H H H tetrasubstituted trisubstituted disubstituted monosubstituted

5 5 2.Acid Catalyzed Dehydration of Alcohols

6 6 Mechanism for Dehydration of Secondary and Tertiary Alcohols: An E1 Reaction Only a catalytic amount of acid is required since it is regenerated in the final step of the reaction Step 1

7 7 Step 2 Step 3

8 8 Carbocation Stability and the Transition State Recall the stability of carbocations is:

9 9 A Mechanism for Dehydration of Primary Alcohols: An E2 Reaction

10 10 Carbocation Stability and the Occurrence of Molecular Rearrangements Rearrangements During Dehydration of Secondary AlcoholsRearrangements of carbocations occur if a more stable carbocation can be obtained

11 11 จงเข ยนกลไกการเก ดปฏ ก ร ยา จงเขยนกลไกการเกดปฏกรยา

12 12

13 13 A hydride shift (migration of a hydrogen with its electrons) can also occur to yield the most stable carbocation

14 14 Carbocation rearrangements can lead to formation of different ring sizes

15 15 3.Dehalogenation of Dihalide

16 16 Reaction of Alkenes 1.Additions to Alkenes

17 17 Addition of hydrogen halides to alkenes: Markovenikov s rule Mech. C C H X C C X - H C H C X

18 18 Ex 1. CH 3 CH CH 2 HBr

19 19 Markovnikov s Rule: addition of HX to an alkene proceeds so that the anion atom adds to the carbon that already has the less hydrogen atoms

20 20 Ex 1. CH 3 CH CH 2 cold CH 3 CHCH 3 Heat CH 3 CHCH 3 H 2 SO 4 OSO 3 H H 2 O OH (Addition of Sulfuric to alkenes)

21 21 Ex 2. H 3 C HC CH 2 HOH 3 4 H 3 PO 4,300 o C H H 3 C C CH 3 OH (Addition of water to alkenes)

22 22 Ex 3. H 3 C 3 H 3 C C Mech. C CH 3 Br 2 /CCl 4 CH 3 H 3 C H 3 C C C Br ส น าตาลแดง สนาตาลแดง ไม ม ส ไมมส Br - Br CH 3 CH 3 C C C C anti-addition Br Br Bromonium ion Br Br Br C C (Halogenation Reaction)

23 anti-addition 23

24 24 Alcohols from Alkenes es Through Oxymercuration- Demercuration: Markovnikov Addition Step 1:Oxymercuration Step 2: Demercuration

25 25

26 26

27 27 -Alcohols from Alkenes through Hydroboration-Oxidation: Anti-Markovnikov Syn Hydration -The reaction leads to syn and anti-markovnikov addition of water to alkenes 1:Hydroboration 2:Oxidation

28 28 Hydroboration: Synthesis of Alkylboranes The elements of hydrogen and boron are added across the double bond

29 29 1:Hydroboration 2:Oxidation S f Alk H d i M h d Summary of Alkene Hydration Methods -Acid-catalyzed hydrolysis: Markovnikov addition -Oxymercuration: Markovnikov addition -Hydroboration-Oxidation: anti-markovnikov and syn addition

30 30 Oxidations of Alkenes: Syn 1,2-Dihydroxylation Either OsO 4 or KMnO 4 will give 1,2 diols (glycols)

31 31 Mechanism for Syn Hydroxylation of Alkenes

32 32 Oxidative Cleavage of Alkenes Reaction of an alkene with hot KMnO 4 results in cleavage of the double bond and formation of highly oxidized carbons

33 33 Unsubstituted carbons become CO 2, monosubstituted carbons become carboxylates and disubstituted carbons become ketones

34 34 Ozonolysis of Alkenes Cleavage of alkenes with ozone and workup with zinc in acetic acid leads to less highly oxidized carbons than products from cleavage with hot KMnO 4

35 35 Unsubstituted carbons are oxidized to formaldehyde, monosubstituted carbons are oxidized to aldehydes and disubstituted carbons are oxidized to ketones

36 36