Chapter14-5 - Chapter 14 Organometallic Compounds Chem 212...

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Chem 212 B. R. Kaafarani 1 Chapter 14 Organometallic Compounds
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Chem 212 B. R. Kaafarani 2 Li Cyclopropyl lithium Vinyl sodium H 2 C CH Na CH 3 CH 2 Mg CH 2 CH 3 Diethyl magnesium CH 3 Mg I Methyl magnesium iodide Metal is the parent 14.1. Organometallic Nomenclature
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Chem 212 B. R. Kaafarani 3 Electronegativities 14.2. Carbon-Metal Bonds in Organometallic Compounds
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Chem 212 B. R. Kaafarani 4 R X δ + R M + Organometallics are a source of nucleophilic carbon (carbanions) 14.2. Carbon-Metal Bonds in Organometallic Compounds
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Chem 212 B. R. Kaafarani 5 CH 3 F CH 3 Li Polarity of Bonds
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Chem 212 B. R. Kaafarani 6 same for Ar —X An oxidation-reduction reaction: carbon is reduced. R X + 2Li R Li + LiX Normally prepared by reaction of alkyl halides with lithium: 14.3. Preparation of Organolithium Compounds
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Chem 212 B. R. Kaafarani 7 (CH 3 ) 3 CCl + 2Li Diethyl ether –10°C (CH 3 ) 3 CLi + LiCl (75%) Br + 2Li Diethyl ether 35°C Li + LiBr (95-99%) Examples
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Chem 212 B. R. Kaafarani 8 R X + Li [R X] + Li + R + X Li R Li Reaction at Metal Surface Reaction with an electron halide occurs at the surface.
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Chem 212 B. R. Kaafarani 9 same for Ar —X R X + Mg RMgX Grignard reagents are prepared by reaction of alkyl halides with magnesium: - Diethyl ether is most often used solvent. - Tetrahydrofuran is also used. - Halide reactivity: I>Br>Cl>F - Reactivity: RX>ArX - Solvent must be DRY! 14.4. Preparation of Organomagnesium Compounds: Grignard Reagents
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Chem 212 B. R. Kaafarani 10 Diethyl ether –10°C (96%) Br + Mg Diethyl ether 35°C MgBr (95%) Cl + Mg MgCl Examples
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Chem 212 B. R. Kaafarani 11 R X + Mg [R X] + Mg + R + X R Mg + Mg + X Electron Bookkeeping
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Chem 212 B. R. Kaafarani 12 Certain groups cannot be present in: - The solvent. - The halide from which the Grignard reagent is prepared. - The substance with which the Grignard reagent reacts. Forbidden Groups Anything with an OH, SH, or NH group. i.e. an acidic hydrogen. Therefore, cannot use H 2 O, CH 3 OH, CH 3 CH 2 OH, etc. as solvents. Cannot prepare Grignard reagent from substances such as HOCH 2 CH 2 Br, etc.
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Chem 212 B. R. Kaafarani 13 R M H OR' •• R H OR' •• •• M + δ δ + Grignard reagents ( M = MgX) and organolithium reagents ( M = Li) are strong bases. 14.5. Organolithium and Organomagnesium Compounds as Brønsted Bases
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Chem 212 B. R. Kaafarani 14 (100%) + H 2 O + LiOH CH 3 CH 2 CH 2 CH 2 Li CH 3 CH 2 CH 2 CH 3 water is a stronger acid than butane Example
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Chem 212 B. R. Kaafarani 15 MgBr (100%) + CH 3 OH + CH 3 OMgBr methanol is a stronger acid than benzene Example
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Chem 212 B. R. Kaafarani 16 Hydrocarbon p K a (CH 3 ) 3 C H 71 CH 3 CH 3 62 CH 4 60 Ethylene 45 Benzene 43 Ammonia 36 Acetylene 26 Water 16 Hydrocarbons are very weak acids. Their conjugate bases
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This note was uploaded on 01/06/2012 for the course CHEM 212 taught by Professor Bilalkaafarani during the Fall '10 term at American University of Beirut.

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Chapter14-5 - Chapter 14 Organometallic Compounds Chem 212...

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