Alkenes and alkynes(l) 9.1 Introduction Additions to alkenes Addition C-C t A-B Ac—c—B We shall study other examples of additions to the double bonds of alkenes. We begin with the additions of hydrogen halides, sulfuric acid water(in the presence of an acid catalyst), and halogens
Alkenes and alkynes (II) 9.1 Introduction: Additions to alkenes We shall study other examples of additions to the double bonds of alkenes. We begin with the additions of hydrogen halides, sulfuric acid, water (in the presence of an acid catalyst), and halogens. C C + A-B A C C B Addition
An Addition reaction HX CC— x Alkyl halide HOSOOH H一c—c—0s02 OH Alkyl hydrogen sulfate HOH Alkene H—c—c—oH Alcohol X-X X一c—c—X Dihaloalkane
An Addition reaction C C H C C X Alkene H X HOSO2OH H C C OSO2OH H C C OH HOH Alkyl halide Alkyl hydrogen sulfate Alcohol X C C X X - X Dihaloalkane
1. An addition reaction results in the conversion of one pi TT -bond and one sigma-bond into two sigma bonds SD Addition C-c X-Y X—c-c-Y 20- Bonds formed Bonds broken
1. An addition reaction results in the conversion of one pi π -bond and one sigma-bond into two sigma bonds C C + X - Y X C C Y Bonds broken 2 - Bonds formed sp 2 sp 3 Addition
2. The electrons of the pi-bond are exposed. Because the pi bond results from overlapping p orbital, the pi electrons lie above and below the plane of the double bond Love elctrons Electrophiles亲电试剂 H. X Lewis acids: Bf2 and alcl Metal ions: Agt. Hg2+. pt2+
2. The electrons of the pi-bond are exposed. Because the pibond results from overlapping p orbital, the pi electrons lie above and below the plane of the double bond: C C sp 2 Electrophiles 亲 电 试 剂 H + , X + , Lewis acids; BF3 and AlCl 3 Metal ions; Ag + , Hg 2+ , Pt 2+ , Love elctrons
bydrogen halides react with alkenes h CI Cl Sloy fast Carbocation(正碳离子) Addition reaction mechanism Ht Cr CI c—C SlOw fast Carbocation(正碳离子)
Hydrogen halides react with alkenes H + Cl - Carbocation (正 碳 离 子 ） H + Cl - H Cl Slow fast C C C C H Cl sp 2 sp 3 H + Cl - H + Cl - slow fast Addition Reaction Mechanism Carbocation (正 碳 离 子 ）
9.2 Addition of Hydrogen Halides to alkenes Markovnikoy' s rule(马氏规则) What is it Mar's Rule?-----The addition of hx to an alkenes, the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms
9.2 Addition of Hydrogen Halides to Alkenes: Markovnikov’s Rule (马氏规则） What is it Mar’s Rule?-----The addition of HX to an alkenes, the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms
Markovnikov's rule(马氏规则) H2C=CHCH3 HX CH2CHCH3 H X Carbon atom with the Markovnikov addition product greater number of hydrogen atoms
H2C CHCH3 + H + X - CH2CHCH3 H X Markovnikov addition product Carbon atom with the greater number of hydrogen atoms Markovnikov’s Rule (马氏规则）
H2c CC +HCI一 CH2C(CH3)2(not CICH, CH(CH3)2 CH H C 2-Methylpropene tert-Butyl chloride Cl CH CH hcl H Methy cyclohexene I-Chloro-1-Methylcyclohexane
H2C CCH3 + HCl CH2C(CH3 ) 2 H Cl (not ClCH2CH(CH3 ) 2 CH3 2-Methylpropene tert-Butyl chloride CH3 + HCl Cl CH3 H Methylcyclohexene 1-Chloro-1-Methylcyclohexane
a mechanism for addition of a hydrogen halide to an alkene (two steps Slow Step l HX rate-determining rep fast Step 2 H X
A mechanism for addition of a hydrogen halide to an alkene (two steps;) Step 1 + HX Slow H + rate-determining step Step 2 H + + X - fast H X
9.2A Theoretical explanation of markovnikov's rule 1. Electronic effects(电子效应 H3C→c=CH2+H-Br CH3CHCH2H (not BrCH2 CHCH3) Br Methyl push electron Markovnikov addition product
9.2A Theoretical explanation of Markovnikov’s Rule C H CH2 + H-Br CH3CHCH2H Br Markovnikov addition product (not BrCH2CHCH3 H ) 3C − + − + H Methyl push electron 1. Electronic Effects (电子效应）