Nucleophilicity Nucleophile strength roughly parallels basicity CH3>NH>OH F Nucleophile strength increases going down a group OH SH F<Cl<Br<I NH;PH3 A base is always a stronger nucleophile than its conjugate acid NH2>NH3 OCH>CH3OH
Nucleophilicity Nucleophile strength roughly parallels basicity C H3 - > NH2 - > OH- > F- Nucleophile strength increases going down a group O H- < SHF - < Cl- < Br- < IN H3 < PH3 A base is always a stronger nucleophile than its conjugate acid OCH3 - > CH3O H N H2 - > NH3
lodide vs.Fluoride as Nucleophiles sp3 orbital little bonding back lobe 人父 H C…X HH F "hard,"small valence shell transition state more bonding H X HH "soft,"large valence shell transition state
Iodide vs. Fluoride as Nucleophiles
Nucleophiles (preferably non-basic) basic non-basic HS>P(CH3)3>CN>I>OCH>OH>Br>CI>NHs OAc
Nucleophiles (preferably non-basic) HS- > :P(CH3 )3 > CN- > I- > OCH3 - > OH- > Br- > Cl- > NH3 > OAcbasic non-basic
Good Leaving Groups are Weak Bases C-LG bond is broken during RDS Quality of leaving groups is crucial Sulfonates are excellent leaving groups O CH: CH3SO- 0 tosylate mesylate TsO- MsO-
Good Leaving Groups are Weak Bases TsO- MsOmesylate C LG bond is broken during RDS Sulfonates are excellent leaving groups O O CH3 SO tosylate CH3 SO O O Quality of leaving groups is crucial
Common Leaving Groups TsO-MsO-NH>1>H2=Br CH>>R Sulfonates are easily pre pared from alcohols in pyridine 0 CH3OH CISR CH3OSR HCI tosylate R= CH: mesylate R=CH 3
Common Leaving Groups TsO- = MsO- > NH3 - > I- > H2O- = Br- > Cl- >> F- Sulfonates are easily prepared from alcohols mesylate R = CH 3 CH3 tosylate R = O O CH3OSR + HCl in pyridine O O CH3OH + ClSR