Chem.62.Chapt18

Chem.62.Chapt18 - Chapter 18-1 Derivatives of Carboxylic...

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Chapter 18-1 Chem 62 Carboxylic Acid Derivatives Derivatives of Carboxylic Acids Any compound which yields a carboxylic acid on hydrolysis (acid or base) with water CH 3 C O OCH 3 CH 3 C O NH 2 CH 3 C O Cl CH 3 C O O CH 3 C O CH 3 C N nitrile anhydride acid chloride amide ester Reactivity CH 3 C O X X = OR, Cl, NH 2 , OCOR leaving groups X = H, R, Ar not leaving groups Aldehydes and ketones undergo nucleophilic addition Carboxylic acid derivatives undergo nucleophilic substitution due to the presence of a leaving group on the carbonyl carbon Nucleophilic acyl substitution CH 3 C O X CH 3 C O X Nu CH 3 C O X + X tetrahedral (sp3) intermediate Nu: R C O O Reactivity of carboxylc acid derivatives decreases with increasing basicity of leaving group increasing basicity of acyl substituent (leaving group) decreasing reactivity (leaving group ability) < OR < NH 2 < CH 3 X < Acid chlorides and anhydrides react readily with water while esters and amides are fairly stable toward water and require acid or base to effect hydrolysis Reacticvity is also related to the resonance donating ablity of the acyl substituent R R C O Cl + C O Cl CH 3 R CH 3 R C O O C O O + R R C O O C O O + CH 3 CH 3 R CH 3 CH 3 R C O N C O N: + R O R O best resonance donor since nitrogen is least electronegative and better Lewis base: Amides have significant C=N double bond character and hindered rotation about the N– Cacrbonyl bond. R C O O + R O
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Chapter 18-2 Chem 62 Acid Halides Preparation C C O OH CH 3 CH 2 CH 2 C O Cl CH 3 CH 2 CH 2 C O OH O Cl PCl 3 , heat SOCl 2 , heat Reactions of Acid Halides most reactive of the carboxylic acid derivatives since the halide ion is a good leaving group. R C O Cl R C Nu O Cl R C O Nu tetrahedral intermediate elimination addition + Cl - Nu: overall net substitution of Nu for Cl Hydrolysis R C O Cl R C OH 2 O Cl R C O O R C O OH + HCl - H + + tetrahedral intermediate + + Cl Rate decreases with increasing size of R since water solubility decreases Ester formation C O Cl N C O OCH 2 CH 2 CH 3 N + H + pyridine reacts with HCl to remove it from the reaction H H Amide formation R C O Cl R C NH 3 O Cl R C O NH 3 R C O NH 2 + HCl - H + + tetrahedral intermediate + + Cl CH 3 C O Cl CH 3 C O NHCH 3 C O Cl C O N CH 3 CH 3 + (CH
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This note was uploaded on 03/15/2009 for the course CHEM 262 taught by Professor Forbes during the Spring '08 term at UNC.

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Chem.62.Chapt18 - Chapter 18-1 Derivatives of Carboxylic...

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