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 8 Alkenes and Alkynes II：（8.1-8.4）Introduction：Additions to Alkenes

Chapter 8 Alkenes and Alkynes l: Addition Reactions

Chapter 8 Alkenes and Alkynes II: Addition Reactions

ORGANIC CHEMISTRY Chapter 8 8.1 Introduction Additions to alkenes Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 8 8.1 Introduction: Additions to Alkenes

ORGANIC CHEMISTRY Chapter 8 =C A-B A-C-C-B Electrophilic addition H-X H-C-C-X H-OSO3H H-C-C-OSO,H C=C H-OH H-C-C-OH HA X-X X-C-C-X Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 8 C C X X H OSO3H H OH H X H C C X H C C OSO3H H C C OH X C C X HA C C + A B A C C B Electrophilic addition

ORGANIC CHEMISTRY Chapter 8 Electrophiles Are Lewis Acids A-B+C=C、 C-C Electrophile Nucleophile Carbocation B Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 8 Electrophiles Are Lewis Acids A B + C C C C A + B C C A B Electrophile Nucleophile Carbocation

ORGANIC CHEMISTRY Chapter 8 8.2 Addition of Hydrogen halides to Alkenes: Markovnikov's rule Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 8 8.2 Addition of Hydrogen Halides to Alkenes: Markovnikov’s Rule

ORGANIC CHEMISTRY Chapter 8 C=C、+H-X H-C Reactivity: HI >HBr> HCI >HF (CH3)2C=CH2>CH3 CH=CHCH3> CH3CH=CH2>CH2=CH2 HOAC CH3 CH,CH=CH,+ HBr Ch2 CHo-CH-CH Br CH3 80% HOAC (CH3hC-CH2+HCl CH3-C—CH 100 Markovnikov's Rule: In the addition of hX to alkene the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 8 C C + H X H C C X Reactivity: HI >HBr > HCl >HF (CH3)2C CH2 CH3CH CHCH3 CH3CH CH2 CH2 CH2 > >~~ > CH3CH2CH CH2 + HBr (CH3)2C CH2 CH Br CH3CH2 CH3 + HCl C Cl CH3 CH3 CH3 80% 100% HOAc HOAc Markovnikov’s Rule: In the addition of HX to alkene the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms

ORGANIC CHEMISTRY Chapter 8 Markovnikoy's rule o In the addition of HX to an unsymmetrically substituted alkene, the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms and that the x group adds to the carbon having more alkyl substituents o Markovnikov's rule can be restated by saying that, in the addition of hX to an alkene, the more stable carbocation intermediate is formed Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 8 Markovnikov’s rule In the addition of HX to an unsymmetrically substituted alkene, the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms and that the X group adds to the carbon having more alkyl substituents. Markovnikov’s rule can be restated by saying that, in the addition of HX to an alkene, the more stable carbocation intermediate is formed

ORGANIC CHEMISTRY Chapter 8 Mechanism SlOW Step I C=C、+HⅩ H-C-C fast Step 2 H-c-C- + X H-C-C-X Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 8 Mechanism Mechanism C C + H X H C C slow Step 1 H C C + X H C C X fast Step 2

ORGANIC CHEMISTRY Chapter 8 8.2A Theoretical Explanation of Markovnikov's rule Br CH2CHCH CH2 CHCHoBr 1° Carbocation Bromopropane H-Br CH3 CH= 2 (ess stable (little formed Br CH3 CHCH3 - CH2 CHCH 2° Carbocation B (more stable) 2-Bromopropane (main product) Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 8 8.2A Theoretical Explanation of Markovnikov’s Rule CH3CH CH2 H Br CH3CH2CH2 CH3CHCH3 1° Carbocation 2° Carbocation (more stable) (less stable) Br Br CH3CH2CH2Br CH3CHCH3 Br (main product) (little formed) 1-Bromopropane 2-Bromopropane

ORGANIC CHEMISTRY Chapter 8 8. 2B Modern statement of Markovnikov's rule o In the ionic addition of an unsymmetrical reagent to a double bond, the positive portion of the adding reagent attaches itself to a carbon atom of the double bond so as to yield the more stable carbocation as an intermediate H2C、 Cl CH3 C=CH I C-CH2—H2C-C-CH H2C HC Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 8 8.2B Modern Statement of Markovnikov’s Rule In the ionic addition of an unsymmetrical reagent to a double bond, the positive portion of the adding reagent attaches itself to a carbon atom of the double bond so as to yield the more stable carbocation as an intermediate. C CH2 H3C H3C I Clδ δ + C CH2 H3C H3C I Cl H3C C CH2 CH3 Cl I