14. Derivatives of Carboxylic Acids

14. Derivatives of Carboxylic Acids - 2010 Department of...

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© 2010 Department of Chemistry, The University of Western Ontario 14.2 14. Derivatives of Carboxylic Acids (text 15.1 – 15.6) A. Structure and Nomenclature We’re interested in four derivatives, each of which has a group bonded to an acyl carbon: X O R acyl halide OR' O R ester O O R O R' anhydride NR' 2 O R amide The names of the derivatives come from the carboxylic acid. For esters, change ic acid to ate , preceded by the name of the alkyl group on the ester alcohol group. OH O CH 3 acetic acid OCH 2 CH 3 O CH 3 ethyl acetate Cyclic esters are lactones and are designated using Greek letters ( , , , , , etc.), depending on the number of carbon atoms that the ester oxygen is from the carbonyl. O O O O a –lactone a –lactone
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14.2 For acid halides, change ic acid to yl halide . OH O propanoic acid Cl O propanoyl chloride For symmetrical anhydrides, change acid to anhydride . Anhydrides are usually formed by coupling two carboxylic acids with the loss of water (hence the name anhydride) OH O CH 3 acetic acid O O CH 3 acetic anhydride CH 3 O H 2 O H O O CH 3 Cyclic anhydrides are formed by heating dicarboxylic acids. HO OH O O OH OH O O H 2 O O O O = For amides change oic acid or ic acid to amide . If the amide N has groups other than H, their attachment to the nitrogen is designated by the prefix N . OH O NH 2 O N O benzoic acid benzamide N , N -dimethylbenzamide
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14.3 Cyclic amides are called lactams . When two acyl groups form amide bonds to the same N atom (like an anhydride), we get an imide . Designate with Greek letters. NH O a –lactam H N O O an imide B. Spectroscopy All acid derivatives contain a strong C=O stretch near the 1630 – 1800 cm −1 region. Esters also have two peaks due to the C–O stretch around 1050 and 1250 cm −1 . e.g. ethyl butanoate
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14.4 Carbon- and proton-NMR spectra of ethyl butanoate Amides have a C=O stretch near 1650 cm −1 and the usual N–H peaks near 3330. e.g. N -methylbenzamide.
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14.5 Carbon- and proton-NMR spectra of N -methylbenzamide C. Reactivity of Acid Derivatives The characteristic reaction of all acid derivatives is nucleophilic acyl substitution . The nucleophile is added followed by the elimination of the leaving group. LG O R Nu O R Nu LG The reactivity of an acid derivative towards nucleophilic acyl substitution depends on two factors: o How electrophilic the acyl carbon is (how likely the carbon is to be attacked by the nucleophile), and o The ability of LG to act as a leaving group.
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14.6 1. Electrophilicity of the acyl carbon As seen in aldehydes and ketones, a resonance structure can be drawn for the carbonyl group. The carbon atom is electrophilic. R
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This note was uploaded on 05/01/2011 for the course CHEMISTRY Chemistry taught by Professor Dr.felixlee during the Fall '11 term at UWO.

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14. Derivatives of Carboxylic Acids - 2010 Department of...

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