215F07-notes-10-5-07

215F07-notes-10-5-07 - Chem 215 F07 Notes Dr. Masato...

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Chem 215 F07 Notes – Dr. Masato Koreeda - Page 1 of 4. Date: October 5, 2007 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
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215F07-notes-10-5-07 - Chem 215 F07 Notes Dr. Masato...

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