Dolbier HW Solutions 564

Dolbier HW Solutions 564 - 658 ARYL HALIDES Elimination of...

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Unformatted text preview: 658 ARYL HALIDES Elimination of fluoride ion from the cyclohexadienyl anion intermediate restores the aromaticity of the ring and completes the reaction. F F F F F F OCH3 F F OCH3 F Cyclohexadienyl anion intermediate 23.6 F F F 2,3,4,5,6-Pentafluoroanisole Fluoride ion 4-Chloropyridine is more reactive toward nucleophiles than 3-chloropyridine because the anionic intermediate formed by reaction of 4-chloropyridine has its charge on nitrogen. Because nitrogen is more electronegative than carbon, the intermediate is more stable. Cl Y Cl Y N N 4-Chloropyridine Anionic intermediate (more stable) Cl Y Cl Y N N 3-Chloropyridine 23.7 Anionic intermediate (less stable) The aryl halide is incapable of elimination and so cannot form the benzyne intermediate necessary for substitution by the elimination–addition pathway. CH3 Br (No protons ortho to bromine; elimination is impossible.) CH3 2-Bromo-1,3dimethylbenzene 23.8 The aryne intermediate from p-iodotoluene can undergo addition of hydroxide ion at the position meta to the methyl group or para to it. The two isomeric phenols are m- and p-methylphenol. CH3 CH3 NaOH, H2O NaOH, H2O (elimination phase) (addition phase) I p-Iodotoluene CH3 CH3 OH OH m-Methylphenol Back Forward Main Menu TOC p-Methylphenol Study Guide TOC Student OLC MHHE Website ...
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This note was uploaded on 10/03/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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