有机光谱化学分析 (30).pdf

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1、P1：Hello everyone,welcome to organic spectroscopic analysis course.In last lecture,we have learned the selection rule of IR spectroscopy.In this lecture,we are going to learn the factors of influencing vibrational frequencies.大家好，欢迎学习今天的课程有机波谱分析。在上一堂课中，我们学习了红外光谱的选率。这一节课，我们将学习影响振动频率的因素。P2:The first f

2、actor is the status of molecule.Frequency in gas is bigger than that in liquid,and much bigger than that in solid.N-methylethylamine in its liquid state forms clusters,which makes C=O less stronger than that in solution，c=o shifts to lower frequency 1650cm-1 第一个因素是分子的状态。气态频率大于液态并且远大于固体的频率。N-甲基乙胺在液态时

3、形成聚合物，这使 C=O 的伸缩振动频率不如溶液中强，c=o 移至低频 1650cm-1 P3:For a simple harmonic oscillator,the frequency of a stretching vibration is given by an equation drived from Hooks law for a vibrating spring,where N is the Avogadros number,c is the velocity of light,K is the force constant,and a measure of the bond s

4、trength,is the reduced mass.对于简谐振荡，伸缩振动的频率由霍克定律推导的弹簧方程式给出，其中 N 是阿伏加德罗数，c 是光速，K 是键力常数，量度键的强度，为折合的质量。P4:Frequency decreases with increasing atomic weight.Frequency increases with increasing bond energy.频率随着原子量的增加而降低。频率随着键能的增加而增加。P5:Electron-withdrawing group makes the absorption peak shift to high fre

5、quency(Induction effect).吸电子基团使吸收峰向高频方向移动（诱导效应）。P6:Due to the different electronegativity of the substituents,the distribution of electron clouds in the molecule is changed by the induction effect,which changes the force constant of the bond and the characteristic absorption frequency of the group.由

6、于取代基的电负性不同，分子中电子云的分布通过诱导效应而改变，从而改变了键力常数和基团的特征吸收频率。The carbonyl group is a strongly polar group.Due to the large electronegativity of the oxygen atom,the electron cloud of the carbon-oxygen bond is approaching to oxygen atom.羰基是强极性基团，由于氧原子的大负电性，碳-氧双键的电子云接近氧。Generally,the force constant of the double

7、bond is greater than that of the single bond,so any effect of increasing the form of the single bond or enhancing the polarity will reduce the force constant of the carbonyl bond and cause the stretching vibration frequency of the carbonyl group to move to a low wave number.通常，双键的键力常数大于单键的键力常数，因此，任何

8、增加单键性或增强极性的作用都会降低羰基的键力常数，并引起碳羰基伸缩振动频率移至低波数。Conversely,when an electron-withdrawing group is connected to the carbon atom of the carbonyl group,the polarity of the carbonyl group is weakened,the carbon-oxygen bond force constant is increased,and the absorption band moves toward a high wavenumber.相反，当

9、吸电子基团连接到羰基的碳原子上时，羰基的极性减弱，碳-氧键力常数增加，吸收带向高波数方向移动。P8:Conjugation effect: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 direction(red shift).共轭效应：共轭效应常引起 C=O 双键的极性增强，双键性降低，伸缩振动频率向低频

10、方向移动（红移）。The CC,C N bond existing in the conjugate system,its stretching vibration frequency also moves to the low wave number direction(red shift).存在于共轭体系中的 CC，C N 键，其伸缩振动频率也向低波数方向移动（红移）。P9:In these examples,p-conjugation makes C=O move to a low frequency.conjugation makes C=O move to a low frequen

11、cy too.在这些示例中，p-C=O 向低波数移动。C=O 向低波数移动。P12:Field effect is not through chemical bonds,but the effect of electrostatic fields through space.场效应不是通过化学键，而是通过空间静电场的作用。In the three-dimensional configuration of the molecule,only when the interesting groups in certain spatial structure are close to each oth

12、er,will the field effect occur.在分子的三维构型中，只有当某些空间结构中所研究的基团彼此靠近时，才会发生场效应 The field effect is not through chemical bonds,but the electrostatic fields of atoms or atomic groups interact through space.场效应不是通过化学键，而是原子或原子团的静电场通过空间相互作用。P13:Steric effects includes ring force and steric hindrance Effects.立体效应

13、包括环张力和空间位阻的影响 The double bond outside the ring moves to a higher wavenumber as the ring tension increases.随着环张力的增加，环外的双键向高波数移动。In contrast,the double bond inside the ring moves to a lower wavenumber as the ring tension increases 相反，当环张力增加时，环内部的双键向低波数移动。P15:The effect of steric hindrance refers to th

14、e presence of certain groups in the molecule,when the steric hindrance affects the normal conjugation effect or hybrid state in the molecule,resulting in displacement of the vibrational band.位阻效应是指当分子中某些基团的存在时，空间位阻影响分子中正常的共轭效应或杂化状态，导致振动带发生位移。The introduction of the methyl group on the olefinic carbo

15、n prevents the carbonyl and the C=C double bond from being on the same plane.在烯烃碳上引入甲基导致羰基和 C=C 双键不在同一平面上。Therefore,their degree of conjugation decreases,the double bond character of the carbonyl group increases.The vibration shifts to a high wave number.因此，它们的共轭度降低，羰基的双键性增加，振动向高波数移动。P16:Transannula

16、r effects also influent the vibrational frequencies in IR spectra.跨环效应也会影响红外光谱中的振动频率。P17:Due to the formation of hydrogen bonds,the force constant of the chemical bonds participating in the formation of hydrogen bonds is reduced,and the absorption frequency moves to a low wave number.由于氢键的形成，参与氢键形成的

17、化学键的力常数降低，吸收频率向低波数移动。At the same time,the change in dipole moment during vibration increases,so the absorption intensity increases.When hydrogen bonds are formed in the molecule,the absorption frequency can be shifted to a lower wave number.同时，振动过程中偶极矩的变化增加，因此吸收强度增加。当分子中形成氢键时，吸收频率可以移至较低的波数。As the co

18、ncentration of the solution increases,the H-bond association degree increases,the band shifts to a low wave number,and the intensity increases and becomes wider.随着溶液浓度的增加，H 键缔合度增加，谱带移至低波数，并且强度增加并谱带变宽。So in this lecture,we have learned about the factors of influencing vibrational frequencies.They are very important for the interpretation of IR spectrum.Thank you for watching!在这节课中，我们学习了影响振动频率的因素。它们对于红外光谱的解释非常重要。谢谢观看！