Notes on Aryl Halides Free Essays

3/22/2012 ARYL HALIDES 2. dislodging responses of diazonium salts ARYL HALIDES General equation: Arâ€X where X = F, Cl, Br or I Examples Structure: ? C-X bonds are shorter and more grounded Bond C-Cl C-Br Ar-X 1. 69 Aâ ° 1. We will compose a custom exposition test on Notes on Aryl Halides or on the other hand any comparable theme just for you Request Now 86 Aâ ° R-X 1. 77 1. 91 ? Dipole minutes are strangely little. Bond C-Cl Preparation: 1. electrophilic sweet-smelling replacement †helpful just on the off chance that one item is acquired C-Br Ar-X 1. 7 D 1. 7 D R-X 2. 10 D 2. 15 D ? Dipole minutes may counteract contingent upon the geometry of the atom. 1 3/22/2012 PHYSICAL PROPERTIES: ? Breaking points †like those of alkyl halides; same patterns ? Softening point †Among disubstituted aryl dihalides, para isomer has uncommonly high MP; ~70 †100  °C higher than ortho and meta isomers ? Dissolvability conduct †insoluble in water; solvent in nonpolar natural solvents †para isomer is less dissolvable than ortho or meta in some random dissolvable ? can be promptly decontaminated by recrystallization Consider: REACTIONS: 1. Electrophilic fragrant replacement (EAS) †review coordinating force (o, p executive) however ring is deactivated toward EAS. 2. Nucleophilic Aromatic Substitution (NAS or SNAr) ipso replacement ? a molecule or gathering other than H is supplanted in the response Reaction Mechanisms For NAS: A. BIMOLECULAR DISPLACEMENT: expansion disposal system; happens under gentle conditions ***the fragrant ring must contain firmly electron †pulling back or electron †drawing in bunches 2 3/22/2012 Observations: 1. Component impact (Bunnett): Aryl halides don't show a lot of distinction in reactivities toward NAS by means of bimolecular uprooting. 2. Aryl fluorides are generally responsive. II. Expansion †quick expulsion of the halogen as X-isn't the rate deciding advance . B. The Benzyne Mechanism: Elimination-expansion instrument †happens under compelling or lively conditions Evidence for the benzyne component: 1. scrambling of the mark †response system: 2. benzyne can't frame if both ortho positions are involved by different gatherings 3/22/2012 D. Wurtz-Fittig Reaction 3. O-bromoanisole and m-bro moanisole give a similar item under the response conditions. Examination: 1. Concoction tests: Test Reagent Br2/CCl4 KMnO4 AgNO3 Result (- ) (- ) (- ) Different REACTIONS OF ARYL HALIDES 1. Metallation Reactions for aryl halides without receptive gatherings Grignard Reaction: 2. IR Spectroscopy C-X assimilations lie in the unique mark locale ? not helpful for investigation 1000 †1350 cm-1 C †F str. 750 †850 cm-1 C †Cl str. 500 †680 cm-1 C †Br str. 200 †500 cm-1 C †I str. Significant pinnacle frequencies 1500, 1600 cm-1 3000 †3100 cm-1 sweet-smelling C †C str. sweet-smelling C †H str. Response with Lithium Metal: Transmetallation †best with ArBr and ArI 4 Instructions to refer to Notes on Aryl Halides, Essay models