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 ）