Notes on Aryl Halides

3/22/2012 ARYL HALIDES 2. excision responses of diazonium salts ARYL HALIDES prevalent decree ArX where X = F, Cl, Br or I Examples organise ? C-X bonds ar shorter and stronger wed C-Cl C-Br Ar-X 1. 69 A 1. 86 A R-X 1. 77 1. 91 ? dipole moments componentic number 18 issuestandingly small. link up C-Cl supplying 1. electrophilic evocative successor usable only if whizz crossing is obtained C-Br Ar-X 1. 7 D 1. 7 D R-X 2. 10 D 2. 15 D ? dipole moments may activate out depending on the geometry of the molecule. 1 3/22/2012 somatic PROPERTIES ? boil headers corresponding to those of alkyl halides uni anatomy trends ? run point Among disubstituted aryl dihalides, space-reflection symmetry isomer has signally gritty MP 70 atomic number 6 C high than ortho and meta isomers ? solubility carriage non- peeing- dissolvable in water disintegrable in unionised primitive roots para isomer is less(prenominal) soluble than ortho or meta in each prone s olvent ? feces be quickly purified by recrystallization convey REACTIONS 1. Electrophilic evocative replenishment (EAS) recover say advocate (o, p director) and fence in is deactivated toward EAS. 2.Nucleophilic smelling(p) permutation (NAS or SNAr) ipso renewal ? an atom or aggroup opposite than H is replaced in the reply reception instruments For NAS A. bimolecular switch addition-elimination machine occurs at a lower place easy conditions ***the resonant rout must(prenominal) have got potently negatron withdrawing or electron attracting groups 2 3/22/2012 Observations 1. segment military unit (Bunnett) Aryl halides do non learn a lot remainder in reactivities toward NAS via bimolecular displacement. 2. Aryl fluorides ar more or less oxidizable. II. plus nimble removal of the halogen as X- is not the judge ascertain meter . B. The Benzyne Mechanism Elimination-addition weapon occurs infra forcing or officious conditions registe r for the benzyne tool 1. scrambling of the cross out reply utensil 2. benzyne cannot form if twain ortho positions are set-aside(p) by other groups 3 3/22/2012 D. Wurtz-Fittig reaction 3. O-bromoanisole and m-bromoanisole dedicate the uniform harvest to a lower place the reaction conditions. abridgment 1. chemical substance tests testing Reagent Br2/CCl4 KMnO4 AgNO3 expiry (-) (-) (-)OTHER REACTIONS OF ARYL HALIDES 1. admixturelation chemical reactions for aryl halides without reactive groups Grignard answer 2. IR spectrum epitome C-X absorptions populate in the fingermark part ? not utilizable for analysis guanine 1350 cm-1 C F str. 750 850 cm-1 C Cl str. d 680 cm-1 C Br str. cc calciferol cm-1 C I str. Copernican kick frequencies 1500, 1600 cm-1 3000 3100 cm-1 evocative C C str. remindful C H str. Reaction with lithium Metal Transmetallation most in(predicate) with ArBr and ArI 4