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organic chemistry21.ppt

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organic chemistry21.ppt
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Chapter 2 Polar covalent bonding , Acids and Bases,Chapter 3,2,Reactions and Their Mechanisms机理 There are four general types of organic reactions Substitutions取代Additions加成Eliminations消除,Chapter 3,3,Rearrangements重排Cleavage of Covalent Bonds Homolysis均裂Heterolysis异裂,Chapter 3,4,Heterolytic reactions almost always occur at polar bonds The reaction is often assisted by formation of a new bond to another molecule,Chapter 3,5,Introduction to Acid-Base Chemistry Brønsted-Lowry Definition of Acids and Bases Acid: a substance that can donate a proton质子 Base: a substance that can accept a proton Example Hydrogen chloride is a very strong acid and essentially all hydrogen chloride molecules transfer their proton to water,Chapter 3,6,Example Aqueous hydrogen chloride and aqueous sodium hydroxide are mixed The actual reaction is between hydronium and hydroxide ions,Chapter 3,7,Lewis Definition of Acids and Bases Lewis Acid: electron pair acceptor Lewis Base: electron pair donor Curved arrows show movement of electrons to form and break bonds,Chapter 3,8,Opposite Charges Attract and React BF3 and NH3 react based on their relative electron densities BF3 has substantial positive charge on the boron NH3 has substantial negative charge localized at the lone pair,Chapter 3,9,Heterolysis of Bonds to Carbons: Carbanions and Carbocations 负碳离子 与 正碳离子 Reaction can occur to give a carbocation or carbanion depending on the nature of ZCarbocations have only 6 valence electrons and a positive charge,Chapter 3,10,Carbanions have 8 valence electrons and a negative chargeOrganic chemistry terms for Lewis acids and bases Electrophiles亲电体 (“electron-loving” reagents ): seek electrons to obtain a stable valence shell of electrons Are electron-deficient themselves e.g. carbocations Nucleophiles亲核体 (“nucleus-loving” reagents): seek a proton or some other positively charged center Are electron-rich themselves e.g. carbanions,Chapter 3,11,The Use of Curved Arrows in Illustrating Reactions Curved arrow
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