Group frequencies ethers

Phenols (ArOH) also show both these bands, but the C 0 stretching appears at somewhat higher frequencies. Ethers show C—O stretching, but the 0-—H band is absent. Carboxylic acids and esters show C—O stretching, but give absorption characteristic of the carbonyl group, C O, as well. (For a comparison of certain oxygen compounds, see Table 20.3, p. 689.)... 

Alcohols and phenols contain the C—OH group, and ethers the C—O—C group, and so these types of compounds therefore display the C—O stretching vibration. This occurs in the fingerprint region, couples with other modes and is of variable frequency, usually absorbing between 1300 and 1000 cm" Its redeeming features are that it is usually the most intense band in the spectrum and can thus often be used for compound identification. 

These spectra were plotted from runs on a Jarrell-Ash 25-300 Raman spectrophotometer with a 4880 A argon ion laser. In some spectra the region from 4000 to 2000 cm" has been plotted so that the intensity is 0.5 times its true value compared to the rest of the spectrum. These are marked xO.5. Like the infrared spectra, these Raman spectra illustrate a group frequencies which are labeled directly on the spectra. Groups illustrated include alkanes in spectra 1-6, cyclohexanes 7-8, aromatics 9-12,15,17,18,20,21,25, 32-34, double bonds 13,14,24, isocyanate 15, triple bond 16, nitrile 17,18, carbonyls 19-26, alcohols 27-29, ether 30, amines 31, 32, nitro 33, C—Cl 34, C Br 35, and mercaptan 36. A molecular formula index of the Raman spectra follows. 

There is also a noticeable increase in intensity of the aryl-0 band at 1223 cm, especially in the early aging stages. This indicates some association, probably through H-bonding, between the N or OH group and the phenyl ether. It is known that interaction not only shifts the frequency but also increases the intensities of an IR band (11). The association between N and 0 was evidenced by IR spectroscopy (12) and the intensity increase of the 1240cm l... 

In the bisbenzylisoquinolines the size of the macrocyclic system affects the chemical shifts of some groupings of protons in a characteristic way. In certain conformations of the 21-membered ring in 5-7 ether linked systems the 2- and 6-substituents lie over aryl rings with a consequent shift to lower frequency. This is illustrated by the H NMR spectrum of thalictine [39] (38) which shows absorption for the 8-and 8 -protons to low frequency of the other aromatic protons. 

Comparison may be made with repandine [40] (8-7 ether linked system) in which the 18-membered ring forces close approach of parts of the molecule so that some of the methoxyl group protons absorb at lower frequency (see 5 3 37 6 -OMe, d 3-01 7-OMe). 

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