CHAPTER FOURTEEN Organometallic Compounds Having gained one electron, the alkyl halide is now negatively charged and has an odd number of electrons. It is an anion radical. The extra electron occupies an antibonding orbital. This anion radical fragments to an alkyl radical and a halide anion Anion radical Alkyl radical Halide anion Following fragmentation, the alkyl radical rapidly combines with a lithium atom to form the organometallic compound Alkyl radical Lithium Alkyllithium 14.4 PREPARATION OF ORGANOMAGNESIUM COMPOUNDS GRIGNARD REAGENTS The most important organometallic reagents in organic chemistry are organomagnesium compounds. They are called Grignard reagents after the French chemist Victor Grignard. Grignard developed efficient methods for the preparation of organic deriva- tives of magnesium and demonstrated their application in the synthesis of alcohols. For these achievements he was a corecipient of the 1912 Nobel Prize in chemistry who as Grignard reagents are prepared from organic halides by reaction with magnesium, a group ll metal ed to cat- RMgx alkenes Organic halide Magnesium Organomagnesium halide (R may be methyl or primary, secondary, or tertiary alkyl; it may also be a cycloalkyl alkenyl, or aryl group. ○xM=○ Cyclohexyl chloride Magnesium Cyclohexylmagnesium chloride(96%) Bromobenzene Magnesium Phenylmagnesium bromide(95% Anhydrous diethyl ether is the customary solvent used when preparing organo- magnesium compounds. Sometimes the reaction does not begin readily, but once started, it is exothermic and maintains the temperature of the reaction mixture at the boiling point of diethyl ether(35°C) The order of halide reactivity is I> Br >Cl>F, and alkyl halides are more reac- tive than aryl and vinyl halides. Indeed, aryl and vinyl chlorides do not form Grignard Recall the structure of reagents in diethyl ether. When more vigorous reaction conditions are required, tetrahy tetrahydrofuran from Sec. drofuran(THF) is used as the solvent. CH,=CHCI CH,-CHMgCI Vinyl chloride Viny magnesium chloride(92%) Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteHaving gained one electron, the alkyl halide is now negatively charged and has an odd number of electrons. It is an anion radical. The extra electron occupies an antibonding orbital. This anion radical fragments to an alkyl radical and a halide anion. Following fragmentation, the alkyl radical rapidly combines with a lithium atom to form the organometallic compound. 14.4 PREPARATION OF ORGANOMAGNESIUM COMPOUNDS: GRIGNARD REAGENTS The most important organometallic reagents in organic chemistry are organomagnesium compounds. They are called Grignard reagents after the French chemist Victor Grignard. Grignard developed efficient methods for the preparation of organic deriva￾tives of magnesium and demonstrated their application in the synthesis of alcohols. For these achievements he was a corecipient of the 1912 Nobel Prize in chemistry. Grignard reagents are prepared from organic halides by reaction with magnesium, a Group II metal. (R may be methyl or primary, secondary, or tertiary alkyl; it may also be a cycloalkyl, alkenyl, or aryl group.) Anhydrous diethyl ether is the customary solvent used when preparing organo￾magnesium compounds. Sometimes the reaction does not begin readily, but once started, it is exothermic and maintains the temperature of the reaction mixture at the boiling point of diethyl ether (35°C). The order of halide reactivity is I  Br  Cl  F, and alkyl halides are more reac￾tive than aryl and vinyl halides. Indeed, aryl and vinyl chlorides do not form Grignard reagents in diethyl ether. When more vigorous reaction conditions are required, tetrahy￾drofuran (THF) is used as the solvent. Mg THF, 60°C Vinyl chloride CH2 CHCl Vinylmagnesium chloride (92%) CH2 CHMgCl diethyl ether 35°C Cl H Cyclohexyl chloride Mg Magnesium H MgCl Cyclohexylmagnesium chloride (96%) diethyl ether 35°C Br Bromobenzene Mg Magnesium MgBr Phenylmagnesium bromide (95%) Organic halide RX Magnesium Mg Organomagnesium halide RMgX Alkyl radical R Lithium Li Alkyllithium R Li Alkyl radical R Halide anion X Anion radical [R ] X 550 CHAPTER FOURTEEN Organometallic Compounds Grignard shared the prize with Paul Sabatier, who, as was mentioned in Chapter 6, showed that finely divided nickel could be used to cat￾alyze the hydrogenation of alkenes. Recall the structure of tetrahydrofuran from Sec￾tion 3.15: O Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website