lecture 18.2

lecture 18.2 - 18-18-1Organic Organic...

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Unformatted text preview: 18-18-1Organic Organic ChemistryChemistryWilliam H. BrownWilliam H. BrownChristopher S. FooteChristopher S. FooteBrent L. IversonBrent L. Iverson18-18-2FunctionalFunctionalDerivatives ofDerivatives ofCarboxylic AcidsCarboxylic Acids18-18-3Characteristic ReactionsCharacteristic ReactionsNucleophilic acyl substitution:Nucleophilic acyl substitution:an addition-elimination sequence resulting in substitution of one nucleophile for anotherTetrahedral carbonyladdition intermediate-++CNuRCYRCNuROYOO:Nu-:Y-Substitution product:18-18-4Characteristic ReactionsCharacteristic Reactionsin the general reaction, we showed the leaving group as an anion to illustrate an important point about them: the weaker the base, the better the leaving groupR2N-RO-ORCO-X-Increasing basicityIncreasing leaving ability18-18-5Characteristic ReactionsCharacteristic Reactionshalide ion is the weakest base and the best leaving group; acid halides are the most reactive toward nucleophilic acyl substitutionamide ion is the strongest base and the poorest leaving group; amides are the least reactive toward nucleophilic acyl substitution18-18-6Reaction with HReaction with H2O - Acid ChloridesO - Acid Chlorideslow-molecular-weight acid chlorides react rapidly with water higher molecular-weight acid chlorides are less soluble in water and react less readilyCH3CClOH2OCH3COHOHCl++Acetyl chloride18-18-7Reaction with HReaction with H2O - AnhydridesO - Anhydrideslow-molecular-weight acid anhydrides react readily with water to give two molecules of carboxylic acidhigher-molecular-weight acid anhydrides also react with water, but less readilyCH3COCCH3O OH2OCH3COHOHOCCH3O++Acetic anhydride18-18-8Reaction with HReaction with H2O - AnhydridesO - AnhydridesStep 1: addition of H2O to give a TCAIStep 2: protonation followed collapse of the TCAIOCH3-C-O-C-CH3HHO-HOOHHCH3-C-O-C-CH3HHO-HCH3-C-O-C-CH3OOHHH-O-HH+++Tetrahedral carbonyladdition intermediate+OOOCH3-C-O-C-CH3OHOHH+OHHCH3COOOCOCH3HHOHH+CH3C OOOCCH3OHHHHH+H+O18-18-9Reaction with HReaction with H2O - EstersO - EstersEsters are hydrolyzed only slowly, even in...
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lecture 18.2 - 18-18-1Organic Organic...

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