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1、Section 20.21Spectroscopic Analysis ofCarboxylic Acid DerivativesC=O stretching frequency depends on whether thecompound is an acyl chloride, anhydride, ester, oramide.Infrared SpectroscopyCH3CClO1822 cm-1CH3COCH3O1748and1815 cm-1CH3COCCH3OO1736 cm-1CH3CNH2O1694 cm-1C=O stretching frequency nAnhydri

2、des have two peaks due to C=O stretching. One results from symmetrical stretching of the C=Ounit, the other from an antisymmetrical stretch.Infrared Spectroscopy1748and1815 cm-1CH3COCCH3OOC=O stretching frequency nNitriles are readily identified by absorption due to carbon-nitrogen triple bond stret

3、ching in the 2210-2260 cm-1 region.Infrared Spectroscopy1H NMR readily distinguishes between isomericesters of the type:1H NMRRCOROandRCOROOCHis less shielded than OCCH1H NMRCH3COCH2CH3OandFor example:CH3CH2COCH3OBoth have a triplet-quartet pattern for an ethylgroup and a methyl singlet. They can be

4、identified, however, on the basis of chemicalshifts.Chemical shift (d, ppm)Figure 20.901.02.03.04.05.001.02.03.04.05.0CH3COCH2CH3OCH3CH2COCH3O13C NMRCarbonyl carbon is at low field (d 160-180 ppm), but not as deshielded as the carbonyl carbon of an aldehyde or ketone (d 190-215 ppm). The carbon of a CN group appears near d 120ppm.UV-VISCH3CClO235 nmCH3COCH3O225 nmCH3COCCH3OO207 nmCH3CNH2O214 nmnp* absorption: lmaxMost carboxylic acid derivatives give a prominentpeak for an acylium ion derived by thefragmentation shown.Mass Spectrometry+RCXORCX+ORCO+XAmides, however, cleave in the direction