columbia大学有机化学课件20_21 html

1、Section 20.21 Spectroscopic Analysis ofCarboxylic Acid DerivativesC=O stretching frequency depends on whether the compound is an acyl chloride, anhydride, ester, or amide.C=O stretching frequency nOOOOOCH3CClCH3COCCH3CH3COCH3CH3CNH21822 cm-11736 cm-11694 cm-11748and 1815 cm-1Infrared SpectroscopyAnh

2、ydrides have two peaks due to C=O stretching. One results from symmetrical stretching of the C=O unit, the other from an antisymmetrical stretch.C=O stretching frequency nOOCH3COCCH31748and 1815 cm-1Infrared SpectroscopyNitriles are readily identified by absorption due to carbon-nitrogen triple bond

3、 stretching in the 2210- 2260 cm-1 region.Infrared Spectroscopy1H NMR readily distinguishes between isomeric esters of the type:OORCORandRCOROOis less shielded than CCCHH1H NMRFor example:OOCH3COCH2CH3CH3CH2COCH3andBoth have a triplet-quartet pattern for an ethylgroup and a methyl singlet.They can b

4、eidentified, however, on the basis of chemicalshifts.1H NMROOFigure 20.9CH3CH2COCH3CH3COCH2CH35.04.03.02.01.005.04.03.02.01.00Chemical shift (d, ppm)Carbonyl 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

5、CN group appears near d 120 ppm.13C NMRnp* absorption:lmaxOOOOOCH3CClCH3COCCH3CH3COCH3CH3CNH2235 nm207 nm214 nm225 nmUV-VISMost carboxylic acid derivatives give a prominent peak for an acylium ion derived by the fragmentation shown.+ O O +RCXRCXRC X+O Mass SpectrometryAmides, however, cleave in the direction tha