《环境仪器分析》第六章 红外光谱法 (3)

1138000-900
C-O（1300-1000） C-(N、F、P)，P-O，Si-O
面内外弯曲振动
900-650
用于顺反式结构、 取代类型的确定
R
H
C=C
H
R
990 ~ 970 cm-1 面外变形振动吸收峰
R
R
C=C
H
H
690 cm-1 面外变形振动吸收峰
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It has been assumed so far that each band in an infrared spectrum can be assigned to a particular deformation of the molecule, the movement of a group of atoms, or the bending or stretching of a particular bond. This is possible for many bands, particularly stretching vibrations of multiple bonds that are “well behaved”. However, many vibrations are not so well behaved and may vary by hundreds of wavenumbers, even for similar molecules. This applies to most bending and skeletal vibrations, which absorb in the 1500-650 cm-1 region, for which small steric or electronic effects in the molecule lead to large shifts. A spectrum of a molecule may have a hundred or more absorption bands present, but there is no need to assign the vast majority. The spectrum can be regarded as a “fingerprint” of the molecule and so this region is referred to as the fingerprint region.
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常见化合物的特征基团频率分区
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Group Frequencies
The mid-infrared spectrum (4000-400 cm-2)can be approximately divided into four regions and the nature of a group frequency may generally be as follows: the X-H stretching region (4000-2500 cm-1), the tripe-bond region (2500-1900 cm-1), the doublebond region (1900-1300 cm-1) and the fingerprint region (1300-650 cm-1).
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3、有机化合物的定性及结构分析
中红外光谱区可分为4000 ~ 1300 cm-1和1300 ~ 650 cm-1两个区域。最有分析价值的基团频率在 4000 ~ 1300 cm-1之间，这一区域称为基团频率区、 官能团区或特征区。区内的峰时由伸缩振动产生的 吸收带，常用于鉴定官能团。
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1. X-H伸缩振动区（4000 ~ 2500 cm-1） （1）-O-H，3600~3200cm-1,确定醇，酚，酸
在非极性溶剂中，浓度较小（稀溶液）时，峰形尖锐，强 吸收；当浓度较大时，发生缔合作用，峰形较宽。
（2）饱和碳原子上的—C-H
-CH3
2960 cm-1 反对称伸缩振动 2870 cm-1 对称伸缩振动
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2. 叄键（C≡C）伸缩振动区（2500-1900 cm-1）
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Triple-bond stretching absorptions fall in the 2500-2000cm-1 region because of the high force constants of the bonds. C≡C bonds absorb between 2300cm-1 and 2050 cm-1, while the nitrile group (C≡N) occurs between 2300 cm-1 and 2200 cm-1. These groups may be distinguished since C≡C stretching is normally very weak, while C≡N stretching is of medium intensity. These are the most common absorptions in this region, but you may come across some X-H stretching absorptions, where X is a more massive atom such as phosphorus（磷） or silicon（硅）. These absorptions usually occur near 2400cm-1 and 2200cm-1, respectively.
3030 cm-1 3010~ 3206 cm-1 3300 cm-1
3000 cm-1以上
=C-H -CH2
-CH3
1-戊烯的红外光谱
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The fundamental vibrations in the 4000-2500cm-1 region are generally due to O-H,C-H and N-H stretching. O-H stretching produces a broad band that occurs in the range 3700-3600cm-1. By comparison, N-H stretching is usually observed between 3400 cm-1 and 3300 cm-1. This absorption is generally much sharper than O-H stretching and may, therefore, be differentiated. C-H stretching bands from aliphatic compounds （ 脂 类化合物 ） occur in the range 3000-2850 cm-1. If the C-H bond is adjacent to a double bond or aromatic ring, the C-H stretching wavenumber increases and absorbs between 3100 cm-1 and 3000 cm-1.
6.3 试样制备
6.3 Sample Preparation
6.4 红外光谱的应用
6.4 Application of IR
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1、吸收谱带的强度 Intensity of absorption band
红外吸收谱带的强度决定于偶极距变化的 大小。通常把吸收谱带的强度分为5个级别 VS（很强，ε> 200）；S（强，ε为75 ~ 200）；m （中强，ε为25 ~ 75）；W（弱， ε为5 ~ 25）；VW（很弱，ε < 5）。
1300 ~ 650 cm-1区域内，除单键的伸缩振动外，还有因变 形振动产生的谱带。这些振动与整个分子的结构有关。当分 子结构稍有不同时，该区的吸收就有细微的差别，并显示出 分子的特征，因此称为指纹区。指纹区对于指认结构类似的 化合物很有帮助，而且可以作为化合物存在某些基团的旁证。
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芳环取代的倍频峰出现在2000~1668cm-1，强度弱，但很特征。
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1-甲基苯的红外吸收光谱
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3-戊铜的红外光谱图
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乙酸的红外光谱
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丁酸酯的红外光谱
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The principal bands in the 2000-1500 cm-1 region are due to C═C and C═O stretching. Carbonyl（C=O
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4. X-Y，X-H变形振动区 < 1650 cm-1
指纹区（1300~650 cm-1），较复杂。 C-H，N-H的变形振动； C-O，C-X的伸缩振动； C-C骨架振动等。精细结构的区分，例如：CH3在1375 cm-1和1450 cm-1附近同时有吸收，分别对应于CH3的对 称弯曲振动和反对称弯曲振动。
） stretching is one of the easiest absorptions to recognize in an infrared spectrum. It is usually the most intense band in the spectrum, and depending on the type of C=O bond, occurs in the 1830-1650 cm-1region. Note also that metal carbonyls may absorb above 2000 cm-1. C=C stretching is much weaker and occurs at around 1650 cm-1, but this band is often absent for symmetry or dipole moment reasons. C=N stretching also occurs in this region and is usually stronger.