ORGANIC CHEMISTRY. Chapter Cycloalkenes. Department of Chemistry, Xiamen University

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1 ORGANI EMISTRY hapter ycloalkenes Department of hemistry, Xiamen University

2 ORGANI EMISTRY hapter 7 The rings of cycloalkenes containing five carbon atoms or fewer exist only in the cis form. yclopropene yclobutene yclopentene yclohexene Department of hemistry, Xiamen University

3 ORGANI EMISTRY hapter Synthesis of Alkenes via Elimination Reactions Department of hemistry, Xiamen University

4 ORGANI EMISTRY Dehydrohalogenation of Alkyl alides X base X Dehydration of Alcohols hapter 7, heat O O Debromination of vic-dibromides Zn, 3 O 2 Zn 2 Department of hemistry, Xiamen University

5 ORGANI EMISTRY hapter Dehydrohalogenation of Alkyl alides Department of hemistry, Xiamen University

6 ORGANI EMISTRY hapter 7 7.6A E2 reactions: The Orientation of the Double Bond in the Product. Zaitsev s Rule O Na 2 5 O (79%) O Na 2 5 O, (100%) 3 ( 2 ) ( 3) 3 OK ( 3 ) 3 O 40 3 ( 2 ) (85%) Department of hemistry, Xiamen University

7 ORGANI EMISTRY hapter EtO, EtO 3 3 ( 3 ) % 3 31% (more stable) (less stable) EtO 3 The carbon carbon bond has some of the character of a double bond Department of hemistry, Xiamen University

8 ORGANI EMISTRY hapter 7 7.6B An Exception to Zaitsev s Rule 3 ( 3 ) 3 O ( 3 ) 2 ( 3 ) 3 O 27.5% 70 (more substituted) % 3 (less substituted) Department of hemistry, Xiamen University

9 ORGANI EMISTRY hapter The Stereochemistry of E2 Reactions: The Orientation of Groups in the Transition State EtO EtO Anti periplanar transition state (preferred) Syn periplanar transition state (only with certain rigid molecules) Department of hemistry, Xiamen University

10 ORGANI EMISTRY hapter 7 3 ( 3 ) 2 3 ( 3 ) 2 l l EtO l l Department of hemistry, Xiamen University

11 ORGANI EMISTRY hapter Dehydration of Alcohols Department of hemistry, Xiamen University

12 ORGANI EMISTRY O A heat hapter 7 A = 2 SO 4, 3 PO 4, Al 2 O The experimental conditions temperature and acid concentration that are required to being about dehydration are closely related to the structure of the individual alcohol. The relative ease with which alcohols undergo dehydration is in the following order: R 3 O > R 2 O> R 2 O Department of hemistry, Xiamen University

13 ORGANI EMISTRY hapter 7 2. Some primary and secondary alcohols also undergo rearrangements of their carbon skeletons during dehydration O 85% 3 PO % % 3 Department of hemistry, Xiamen University

14 ORGANI EMISTRY hapter 7 7.7A Mechanism for Dehydration of Secondary and Tertiary Alcohols: An E1 Reaction O + 3 O O O Department of hemistry, Xiamen University

15 ORGANI EMISTRY hapter 7 7.7B arbocation Stability and the Transition State R 3 > R 2 > R 2 > 3 δ δ O Transition state Department of hemistry, Xiamen University

16 ORGANI EMISTRY hapter A Mechanism for Dehydration of Primary Alcohols: An E2 Reaction O + A fast O 2 + A slow A + O 2 + A + 2 O Department of hemistry, Xiamen University

17 ORGANI EMISTRY hapter arbocation Stability and the Occurrence of Molecular Rearrangements Department of hemistry, Xiamen University

18 ORGANI EMISTRY hapter O O 2 2 O δ δ more stable alkene less stable alkene Department of hemistry, Xiamen University

19 ORGANI EMISTRY hapter 7 O 3 3 heat O Department of hemistry, Xiamen University

20 ORGANI EMISTRY hapter Alkenes by Debromination of Vicinal Dibromides Department of hemistry, Xiamen University

21 ORGANI EMISTRY hapter 7 X X X X + 2 NaI acetone + I Na Zn or Mg, Ni + ZnX 2 X X Department of hemistry, Xiamen University

22 ORGANI EMISTRY hapter Synthesis of Alkynes by Elimination Reactions Department of hemistry, Xiamen University

23 ORGANI EMISTRY hapter 7 Reaction: R R + 2 R R vic-dibromide 2N 2 R R + 2 N Department of hemistry, Xiamen University

24 ORGANI EMISTRY hapter 7 Mechanism N 2 + R R R R 2 N R R + N 3 + R R R + N 2 R N 2 R R + N 3 + Department of hemistry, Xiamen University

25 ORGANI EMISTRY hapter l 4 NaN Na N 4 l NaN 2 mineral oil O 3 Pl 5 0 l 3 l (1) NaN 2 mineral oil, (2) KO EtO, 3 n NaN 2 mineral oil n Department of hemistry, Xiamen University