ORGANIC CHEMISTRY Chapter 21 21 11 Aryl Halide and nucleophilic Aromatic substitution Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 21 21.11 Aryl Halide and Nucleophilic Aromatic Substitution
ORGANIC CHEMISTRY Chapter 21 o Simple aryl halides are much less reactive than alkyl halides in nucleophilic substitution reactions HO t Naoh no substitution reflux o The c-X bonds of aryl halides are stronger and shorter than those of alkyl halides g aryl cations are very unstable sl do not occur The optimal transition-state geometry required for SN2 processes cannot be achieved no reaction Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 21 Simple aryl halides are much less reactive than alkyl halides in nucleophilic substitution reactions. Cl + NaOH H2O reflux no substitution The C–X bonds of aryl halides are stronger and shorter than those of alkyl halides. Aryl cations are very unstable. SN1 do not occur. The optimal transition-state geometry required for SN2 processes cannot be achieved. Nu X × no reaction
ORGANIC CHEMISTRY Chapter 21 21 11A Nucleophilic Aromatic Substitution by addition-Elimination The Sar mechanism o Nucleophilic substitution can occur when strong electron-withdrawing groups are ortho or para to the halogen atom NO-NO2一CF3=CRCN CO2H -SO3 Br -I-CO2 -C6H5 Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 21 21.11A Nucleophilic Aromatic Substitution by Addition-Elimination: The SNAr Mechanism Nucleophilic substitution can occur when strong electron-withdrawing groups are ortho or para to the halogen atom. N2 N NO NO2 CO2H CF3 CR CN O SO3 Cl Br I CO2 C6H5
ORGANIC CHEMISTRY Chapter 21 C OH 10% NaOH pressur,135~160℃ NO NO NO? Na, CO3, H,O NO 100℃ NO 2 NO 2 CI OH NO NO HO 35°C NO NO Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 21 pressur, 135~160℃ Cl OH NO2 10% NaOH NO2 H+ 100℃ Cl OH NO2 Na2CO3, H2O NO2 NO2 NO2 H+ Cl NO2 O2N NO2 OH NO2 O2N NO2 H2O H+ 35°C
ORGANIC CHEMISTRY Chapter 21 Mechanism u A slow ast +N ddition imination O O O u N N u 00000O-OO Addition-elimination mechanism(加成一消除机制) Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 21 Mechanism Mechanism L N O O + Nu slow L N O O Nu Nu N O O fast addition elimination L N O O Nu L N O O Nu L N O O Nu L N O O Nu Addition-elimination mechanism (加成－消除 机制)