有机波谱分析双语课程 (29).pdf

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1、红外光谱振动频率 有机波谱分析 Organic Spectroscopic Analysis Vibrational Frequencies in IR Factors Influencing Vibrational Frequencies Status 1.Frequencygas liquid solid 2.Solution vs Pure Liquid e.g.CH3CONHCH3(sol.)vs CH3CONHCH3(liq.)b.c.CH3CONHCH3(liq.)forms clusters,which makes C=O less stronger than that in s

2、olution，c=o shifts to lower frequency 1650cm-1 m1m2/(m1+m2)Molecular Structure 1.Bond strength 112kc Induction effect:Electron-withdrawing group makes the absorption peak shift to high frequency.2.Electronic Effect R-COR C=0 1715cm-1 R-COCl C=0 1800cm-1 F-COF C=0 1928cm-1 2.Electronic Effect Inducti

3、on Effect Induction Effect from low to high:X R 3.Conjugation Effect COH3CCH3COCH3COCH3CO1715168516851660cm-1 cm-1 cm-1 cm-1 Conjugation effect:often causes the polarity of the C=O double bond to increase,the double bond decreases,and the stretching vibration frequency moves to a low frequency direc

4、tion(red shift)3.Conjugation Effect p-conjugation make C=O move to a low frequency conjugation make C=O move to a low frequency 3.Conjugation Effect 4.Field effect:Not through chemical bonds,but the effect of electrostatic fields through space.1750 cm-1 1720 cm-1 4.Field effect:5.Steric hindrance Includes:Ring force and Steric hindrance Effects 环内的环内的CC伸缩振动与以上结果相反，随环张力的增大小伸缩振动与以上结果相反，随环张力的增大小 C=C向低波数位移向低波数位移 如环己烯、环戊烯及环丁烯的如环己烯、环戊烯及环丁烯的 C=C 依次为依次为1645，1610，1566cm1 5.Steric hindrance 5.Steric hindrance 6.Transannular effects(跨环效应跨环效应)C=OC=O 1675cm1675cm-1 1 7.Hydrogen bonding