215 HH W08 notes-Chapter 15-3-12

215 HH W08 notes-Chapter 15-3-12 - Chem 215 HH W08 Notes...

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Chem 215 HH W08 Notes – Dr. Masato Koreeda - Page 1 of 13. Date: March 12, 2008 Chapter 15: Carboxylic Acids and Their Derivatives – Acyl Transfer Reactions O R Z an acyl group bonded to an electronegative atom (Z) R OH O carboxylic acid R X O acid halide* X = halogen R O O acid anhydride R OR' O ester R SR' O thioester R NR' 2 O amide R' O R F O R Cl O R Br O acid fluoride acid chloride acid bromide R I O acid iodide * acid halides R C Z O sp 2 hybridized; trigonal planar making it relatively "uncrowded" The electronegative O atom polarizes the C=O group, making the C=O carbon "electrophilic." R C Z O R C Z O R C Z O R C Z O ! ! ! The basicity and size of Z determine how much this structure contributes to the hybrid. hybrid Resonance contribution by Z The more basic Z is, the more it donates its electron pair, and the more resonance structure * contributes to the hybrid. * Trends in basicity: Cl O R' O OH OR' NR' 2 weakest base strongest base increasing basicity similar basicity As the basicity of Z increases, the stability of R Z O increases because of added resonance stabilization. R OH O R Cl O R O O R' O R OR' O R NR' 2 O R O O acid chloride acid anhydrides esters carboxylic acids amides caboxylates most stable (least reactive) least stable (most reactive) Relative stabilities of R Z O I. Introduction
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Chem 215 HH W08 Notes – Dr. Masato Koreeda - Page 2 of 13. Date: March 12, 2008 O R H 3 C OH O H 3 C O H 3 C O O H 3 C O O H 3 C NH 2 O CH 3 O H 3 C Cl O II. Acyl-Transfer Reactions A few nomenclature issues: The group obtained from a carboxylic acid by the removal of the OH is called an acyl group, i.e., acetyl group; often abbreviated as Ac • Names of the C 2 C=O derivatives H 3 C O Na O C H 2 CH 3 ethyl acetate acetic acid sodium acetate acetamide acetyl chloride acetic anhydride C N cyano group: considered to be an acid derivative as it can be hydrolyzed to form an amide and carboxylic acid H 3 C C N The suffix -nitrile is added to the name of the hydrocarbon containing the same number of carbon atoms, counting the carbon atom of the CN group. acetonitrile C N H 3 C-CH 2 -CH 2 -CH 2 -C 5 4 3 2 1 benzonitrile pentanenitrile For example, R C Z O Nu "acylating" agent Nucleophilic attack R C O Nu Z For a reaction to occur, Z must be a better leaving group than Nu . Two possible leaving groups The better the leaving group, the more reactive is in nucleophilic acyl substitution. R C Z O Cl O C R' O OR, OH NH 2 > >> >> better leaving group e.g., Cl O O O O OCH 2 CH 3 O SCH 2 CH 3 O O O O N H CH 3 OH O H 3 O + Represents an acylation reaction of H 2 O. SOCl
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This note was uploaded on 02/13/2012 for the course CHEM 215 taught by Professor Koreeda during the Winter '07 term at University of Michigan.

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215 HH W08 notes-Chapter 15-3-12 - Chem 215 HH W08 Notes...

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