《有機(jī)波譜分析雙語(yǔ)課程 (27).pdf》由會(huì)員分享，可在線閱讀，更多相關(guān)《有機(jī)波譜分析雙語(yǔ)課程 (27).pdf（14頁(yè)珍藏版）》請(qǐng)?jiān)趨R文網(wǎng)上搜索。

1、紅外光譜和選律 有機(jī)波譜分析 Organic Spectroscopic Analysis IR Spectrum and selection rule IR spectrum of CO2 A=lg I0/I=lg 1/T Typical IR Spectra Number of Vibrational Modes Nonlinear molecule with n atoms usually has 3n-6 fundamental vibrational modes.Linear molecule with n atoms usually has 3n-5 fundamental vib

2、rational modes.O=C=O;S=C=S Number of Vibrational Modes a molecule containing N atoms is said to have 3N degrees of freedom.3 degrees of freedom of the translational motion.23 degrees of freedom of the rotational motion.Number of vibrational modes:3N 6 or 3N 5.Vibration Degrees of Freedom and Selecti

3、on Rules of IR Practice:1)What are the Vibration Degrees of Freedom of H2O?(Answer:3)2)What are the Vibration Degrees of Freedom of CO2?(Answer:4)Vibrations of CO2 IR-Active and Inactive?A polar bond is usually IR-active.A nonpolar bond in a symmetrical molecule such as those homonuclear species of

4、O2,N2,or Cl2,will absorb weakly or not at all.A change in dipole of a vibration IR Selection Rule:For infrared the selection rule states that in order for the photon to be absorbed,the molecule must undergo a change in dipole moment.Vibration Spectroscopy Selection Rule:V1,2,3。At room temperature,th

5、e vast majority of molecules are in the vibrational ground state of V=0,so the main observed band is the transition from V=0 to the fundamental frequency absorption band of V=l.An Alkyne（炔烴）（炔烴）IR Spectrum Number of Experimental Peaks Four factors tend to produce fewer experimental peaks than would

6、be expected.1.No change in dipole of a particular vibration;2.The energies of two or more vibrations are identical or nearly identical;3.The absorption intensity is too low;4.The vibrational energy is in a wavelength beyond the range of the instrument.Number of Experimental Peaks Occasionally more peaks are found than are expected.For example,Overtone(倍頻倍頻)and Combination Bands(合頻合頻)Selection rule Selection rule 容許容許:v=1 overtone peakovertone peak：v=2 2 2 v=3 3 3 combination peak：1+2 difference peak(差頻差頻)：1-2 Overtone(倍頻倍頻)and Combination Bands(合頻合頻)1()22hkE