CNGNGE JOHN MCMURRY CHAPTER 8 Reactions of Alkenes and Alkynes T H I R D E DI TION Organic Chemistry with Biological Applications
CHAPTER 8 Reactions of Alkenes and Alkynes
Alkene Reactions Reactions of Alkenes Addition of a halogen to give 1,2-dihalide Addition of a hypohalous acid to give OH halohydrin Addition of water to give alcohol Alcohol Alkane Addition of hydrogen to give alkane Halohydrin 1,2-Diol Addition of single oxygen to give three- membered cyclic ether:epoxide Addition of two hydroxyl groups to give Carbonyl 1,2-diol 1.2-Dihalide Alkene compound Addition of a hydrogen halide to give halide Oxidative cleavage to form a carbonyl Halide Cyclopropane compound Epoxide Addition of carbene to form cyclopropane
▪ Addition of a halogen to give 1,2-dihalide ▪ Addition of a hypohalous acid to give halohydrin ▪ Addition of water to give alcohol ▪ Addition of hydrogen to give alkane ▪ Addition of single oxygen to give threemembered cyclic ether: epoxide ▪ Addition of two hydroxyl groups to give 1,2-diol ▪ Addition of a hydrogen halide to give halide ▪ Oxidative cleavage to form a carbonyl compound ▪ Addition of carbene to form cyclopropane Reactions of Alkenes Alkene Reactions
8-1 Preparing Alkenes:A Preview of Elimination Reactions Preparation of alkenes:elimination reactions Precursors to alkenes Biological systems-usually alcohols Laboratory-either alcohols or alkyl halides Alkenes and alcohols are chemically related through addition and elimination reactions Alkenes add H2O to form alcohols Alkenes add HX to form halides Alcohols eliminate water to form alkenes Alcohols eliminate HX to form alkenes Addition X-Y Elimination
Preparation of alkenes: elimination reactions Precursors to alkenes ▪ Biological systems – usually alcohols ▪ Laboratory – either alcohols or alkyl halides Alkenes and alcohols are chemically related through addition and elimination reactions ▪ Alkenes add H2O to form alcohols ▪ Alkenes add HX to form halides ▪ Alcohols eliminate water to form alkenes ▪ Alcohols eliminate HX to form alkenes 8-1 Preparing Alkenes: A Preview of Elimination Reactions
Preparing Alkenes:A Preview of Elimination Reactions Dehydrohalogenation Loss of HX from alkyl halide Usually occurs by reaction of an alkyl halide with a strong base H Br KOH KBr CH3CH2OH H20 H H Bromocyclohexane Cyclohexene (81%)
Dehydrohalogenation ▪ Loss of HX from alkyl halide ▪ Usually occurs by reaction of an alkyl halide with a strong base Preparing Alkenes: A Preview of Elimination Reactions
Preparing Alkenes:A Preview of Elimination Reactions Dehydration Loss of water from an alcohol a Usually occurs by treatment of an alcohol with a strong acid CH3 CH3 OH H2S04,H20 THF 50C H20 1-Methylcyclohexanol 1-Methylcyclohexene (91%) Tetrahydrofuran (THF)-a common solvent
Dehydration ▪ Loss of water from an alcohol ▪ Usually occurs by treatment of an alcohol with a strong acid Preparing Alkenes: A Preview of Elimination Reactions