Example of Allylic Halogenation with NBS H.C CH. CH2一Br CH3 CH2 NBS,hv C=C Br- HC CH; H.C CH CH, 2.3-dimethylbut-2-ene 2013 Pearson Educeton.Iine Chapter 6 6
Example of Allylic Halogenation with NBS File Name: AAAKWEA0 Chapter 6 6
The SN2 Reaction H H H-0:+ H-0-C-H + H H hydroxide iodomethane methanol iodide (nucleophile) (substrate) (product) (leaving group) The halogen atom on the alkyl halide is replaced with the (HO). Since the halogen is_ electronegative than carbon, the C-l bond and the iodide ion Chapter 6 7
The SN2 Reaction • The halogen atom on the alkyl halide is replaced with the __________ (HO- ). • Since the halogen is ______ electronegative than carbon, the C—I bond _______ ____________ and the iodide ion _______. Chapter 6 7
SN2 Mechanism H HO: HO- H H HH H nucleophile electrophile transition state product leaving (substrate) group (SN2). Concerted reaction:New bond forming and old bond at same time. ·Reaction is order overall. Rate k[alkyl halide][nucleophile]. Chapter 6
SN2 Mechanism • ___________ _____________ _____________ (SN2). • Concerted reaction: New bond forming and old bond __________ at same time. • Reaction is ________ order overall. • Rate = kr [alkyl halide][nucleophile]. Chapter 6 8
Uses for SN2 Reactions Nuc:”+R-X Nuc-R X- Nucleophile Product Class of Product R-X +-:i: > R-i: alkyl halide R-X+-:OH → R-OH alcohol R X+-:OR R-OR' ether R-X +-:SH R-SH thiol(mercaptan) R-X+-:SR R-SR' thioether(sulfide) R-X+ :NH3 R一NHX amine salt R-X +-:N=N=: R-N-N-N:- azide R-X+-:C=C-R R-C=C-R alkyne R-X+ -:C≡Ng R-C=N: nitrile 0 可 R-X +6--R R-0-C-R ester R-X +:PPh3 [R-PPh3]+-X phosphonium salt nE Chapter 6 9
Uses for SN2 Reactions Chapter 6 9
SN1 Mechanism:Step 1 CH3 +CH3 迫 Formation of carbocation(rate-determining step) Chapter 6 10
Formation of carbocation (rate-determining step) SN1 Mechanism: Step 1 Chapter 6 10