Application knowledge of the hottest infrared spec

2022-08-18
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Application knowledge of infrared spectrophotometer in organic analysis

the combination and arrangement of atomic groups in compounds are determined by the characteristic functional groups appearing in the infrared spectrum

(1) the structure of p-cresol bromide tetrachloride was thought to have three possible structures in the past experiments, but the pressure was slowly increased: it was not identified that the clockwise rotation of the pointer was equal to the higher value of the indication, and then it was determined. Now there is only one structure confirmed by infrared spectroscopy

(2) bimolecular aldehyde condensation alcohol ketone, should be formula (I). If (I) r is replaced by pyridyl, its chemical properties are different from (I), and it has the reaction of ene glycol type, such as (II). However, the 3700cm (-1) - band of free hydroxyl can not be seen in the solution of polar olefins, but there is a total hydrogen bond at 2750cm (-1). It can be seen that it has formed intramolecular hydrogen bonds

(I) hydroxyketone formula (II) ene glycol formula

2 Determination of isomers - stereoisomers and isomers can be identified

(1) determination of CIS trans isomers - the sequence of CIS trans isomer atomic groups has no symmetry center, so the c=c double bond is 1630cm (-1), 724cm (-1), while the trans c=c is at a higher frequency

(2) identification of isomers - isomers with different benzene ring substitution positions can be seen in the 900 ~ 660cm (-1) region of the infrared spectrum. For example, the absorption bands of the three isomers of xylene are very different. The ortho position is 742cm (-1), the meta position is 770cm (-1), and the para position is 800cm (-1). Due to the strong symmetry of p-xylene, its c=c double bond (benzene skeleton) becomes smaller at 1500cm (-1), and the 600cm (-1) band disappears. Vortex flowmeter

such as n-propyl, isopropyl and tert butyl can be seen from the bending vibration of methyl in the infrared spectrum. If there is only one absorption band at 1375cm (-1), it is expressed as n-propyl; If there are double peaks with equal strength at 1375cm (-1), it is isopropyl; If there is a strong weak band at `1390cm (-1) and 1365cm (-1), it is tertiary butyl

the molecular formula of ethanol and methyl ether are exactly the same c2h6o. Ethanol has a hydroxyl absorption band at 3500cm (-1), c-0 stretching vibration at 1050 ~ 1250cm (-1), and hydroxyl bending vibration at 950cm (-1). Methyl ether has no hydroxyl absorption at 3500cm (-1). Its first strength is 1150 ~ 1250cm (-1), and the two isomers are easy to distinguish

3. Inspection of chemical reaction - whether a chemical reaction has been completely carried out can be checked by infrared spectroscopy, because the raw materials have their own characteristic absorption bands to ensure the accuracy and normal operation of the test results and the expected products

for example, when the oxidized secondary alcohol is ketone, the hydroxyl absorption of the raw secondary alcohol should disappear, and the carbonyl of ketone 171cm (-1) should appear in the product before the reaction is complete

4. Analysis of unknown substances - the unknown substances can be separated and purified first, then analyzed by elements, and the molecular formula can be written to calculate the unsaturation. From the infrared spectrum, we can get this unknown thing. What can a stone do? The information of functional groups in Guangzhou shitouzao Environmental Protection Technology Co., Ltd. determines which compound it belongs to. The structure of this compound can be identified by UV and NMR

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