波谱分析课件 Chapter 3 Infrared Spectroscopy-f.pptVIP

Chapter 3 Infrared Spectroscopy Each interatomic bond may vibrate in several different motions (stretching or bending) - vibrational, rotational energy level Absorption of radiation by a typical organic molecule results in the excitation of vibrational, rotational and bending modes would be between 0.75 – 200 μ, or infrared region IR Theory Principles IR energy lower than visible Structural Information from IR Good for confirming certain functional groups - especially: -O-H C=O -C?N and C?C Not good for carbon backbone. Intensities vary so not normally quantitative. electronegativity, vibration mode, conjugation, etc NOT GREAT FOR FIGURING OUT STRUCTURE USED FOR VERIFYING OR ELIMINATING POSSIBLE STRUCTURES. Alkanes (3) υ c-c are within 1250 ~ 800 cm-1, and are weak peaks. Usually they are not specific for compounds and can not be used in IR analysis. Alkenes (1) The big difference of IR spectra between alkanes and alkenes are due to the vibration of =C-H and C-C. The specific peaks of Olefin are: 1. υ C=C-H generally appear in the region 3100 to 3000 cm-1, thus differentiating saturated and unsaturated hydrocarbons. Alkenes (2) 2. The out-of-plane bending vibrations in the 1000 to 650 cm-1 region γC=C-H are often useful in predicting the substitution pattern of the double bond. Olefinic C-H out-of-plane bending frequencies Alkenes (3) 3. The C=C stretching frequency υC=C in the 1600 to 1675 cm-1 region also varies with substitution but to a lesser degree Alkynes (1) It’s not difficult to distinguish alkynes from IR spectra based on the following specific band: 1. The C-H stretching vibration of terminal acetyenes (νC≡C-H )generally appears at 3300 to 3100 cm-1 as a strong sharp band. The peak of νN-H is also in this region, but can be recognized with its broad band Alkynes (2) 2. The C≡C stretching band is found in the region 2150 to 2100 cm-1 if the alkyne is monosubstituted and at 2270 to 2150 cm-1 if disubstituted. The latter are usually qu