厦门大学化学化工学院：《有机化学》课程教学资源（课件讲稿，双语版）Chapter 7 Alkenes and Alkynes I（7.4-7.10）Synthesis of Alkynes by Elimination Reactions

ORGANIC CHEMISTRY Chapter 7 7. 4 Cycloalkenes Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 7 7.4 Cycloalkenes

ORGANIC CHEMISTRY Chapter 7 o The rings of cycloalkenes containing five carbon atoms or fewer exist only in the cis form H H H H H Cyclopropene Cyclobutene Cyclopentene Cyclohexene Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 7 The rings of cycloalkenes containing five carbon atoms or fewer exist only in the cis form. H H H H H H H H Cyclopropene Cyclobutene Cyclopentene Cyclohexene

ORGANIC CHEMISTRY Chapter 7 7.5 Synthesis of Alkenes via Elimination reactions Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 7 7.5 Synthesis of Alkenes via Elimination Reactions

ORGANIC CHEMISTRY Chapter 7 Dehydrohalogenation of Alkyl halides H H H H base C-C H HX H H H Dehydration of Alcohols H H HH heat H H HH HOH OH H H Debromination of vic-Dibromides Br H Zn chr coh H NbR Br H H Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 7 C C H H H H X H base HX C C H H H H Dehydrohalogenation of Alkyl Halides C C H H H H C C H H H H OH H H , heat HOH Dehydration of Alcohols C C H H H H Zn,CH3CO2H ZnBr2 C C H H H H Br Br Debromination of vic-Dibromides

ORGANIC CHEMISTRY Chapter 7 7.6 Dehydrohalogenation of Alkyl Halides Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 7 7.6 Dehydrohalogenation of Alkyl Halides

ORGANIC CHEMISTRY Chapter 7 7.6A E2 reactions. The Orientation of the Double bond in the product. Zaitsey's rule CHO Na CH3 CHCH3 CH5OH55°C CH2-CHCH3 Br (79 CH 3 CHO Na CH CH2CCH CH2-CCH C2HOH,55°C Br (1009%) CH3)3COK CH3(CH2)15 CH2 CH2-Br CH3(CH215 CH2-CH2 (CH3)3 COH 40°C (85%) Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 7 7.6A E2 reactions: The Orientation of the Double Bond in the Product. Zaitsev’s Rule C2H5O Na CH3CHCH3 Br C2H5OH 55°C CH2 CHCH3 (79%) C2H5O Na CH3CCH3 Br C2H5OH, CH3 55°C (100%) CH2 CCH3 CH3 CH3(CH2)15CH2CH2 Br (CH3)3COK 40°C CH3(CH2)15CH2 CH2 (85%) (CH3)3COH

ORGANIC CHEMISTRY Chapter 7 CH3 CH3CH2-C-CH2 EtO, EtOH CH3CH-C(CH3)2 CH3CH2C=CH 70°C Br 69 CH331% (more stable) (less stable) Eto--H CH37丰 H H Br The carbon-carbon bond has some of the character of a double bond Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 7 C Br CH3CH2 CH3 EtO, EtOH CH3CH C(CH3)2 CH3CH2C CH2 69% 31% CH3 CH3 + 70°C (more stable) (less stable) C C H H CH3 H Br EtO H The carbon—carbon bond has some of the character of a double bond

ORGANIC CHEMISTRY Chapter 7 7.6B An Exception to Zaitsev's rule (CH3)3CO CH3CH2C—CH3(3COH CH3CH=C(CH3)2+ Br 27.50 70°C (more substituted) CH3CH2C=CH2 725%CH (less substituted Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 7 7.6B An Exception to Zaitsev’s Rule C Br CH3CH2 CH3 CH3CH C(CH3)2 CH3CH2C CH2 27.5% 72.5% CH3 CH3 + 70°C (more substituted) (less substituted) (CH3)3COH (CH3)3CO

ORGANIC CHEMISTRY Chapter 7 7.6C The Stereochemistry of E2 Reactions The Orientation of Groups in the Transition State EtOH S Eto H Br C-C / Br Anti periplanar Syn periplanar transition state transition state (preferred (only with certain rigid molecules) Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 7 7.6C The Stereochemistry of E2 Reactions: The Orientation of Groups in the Transition State C C Br EtO H C C EtO H Br Anti periplanar transition state (preferred) Syn periplanar transition state (only with certain rigid molecules)

ORGANIC CHEMISTRY Chapter 7 CH3=〈 CH(CH3)CH3)CH(CH3) CI Eto h HH H H H H H

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 7 CH(CH3)2 Cl CH3 CH(CH3)2 Cl CH3 Cl EtO H H H Cl H H H H H