Phenols overtones

Liittke and Mecke (1949) investigated e.g. the position of the second overtone OH vibration of phenol in 18 solvents and found that, on changing from an inert solvent to a solvent which has a strong interaction with the phenol, the OH-band is displaced to longer wavelengths and broadened. In some cases a splitting of the OH-band into two components was also observed. 

We have also added for comparison in Column 2 of Table 1 the date of Sidorov [10] which indicate the shifts of the fundamental rOH band of porous glass upon adsorption of the same compounds from gas. In Column 4 [14] we compare our data with those obtained by Mecke for the shifts of the second overtone (3rOH) band of phenol dissolved in the same liquids. In the last column of the Table the shifts of the fundamental OH frequency of methanol, dissolved in the same solvents... 

FIGURE 2.17. Phenol (Melt). Broad intermolecular hydrogen bonded, O—H stretch, 3244 cm-1. Aromatic C—H stretch, 3052 cm-1. Overtone or combination bands, 2000-1667 cm 1. C—C ring stretch, 1601,1501,1478 cm"1. Inplane O—H bend, 1378 cm 1. C—O stretch, 1231 cm-1. Out-of-plane C—H bend, 815,753 cm 1. Out-of-plane ring C—C bend, 699 cm 1. (Broad) hydrogen-bonded, out-of-plane O—H bend, about 650 cm 1. 

The data from the work of Liittke and Mecke (1292, 1375) for the second overtone of the O—H stretch of phenol also provide a reasonably straight line, as shown by the broken line in Fig. 3-13. The slope of this line is distinctly lower than the corresponding line for the fundamential. Least squares treatments give the results fundamental 0J2Ap + 2.5 cm ... 

TABLE 3-V Intensity, Band Width, and Frequency Shift of the Second Overtone of v, of Phenol in Various Bases ... 

Exactly the opposite has been observed, as shown, for example, by phenol in various bases (1292, 1375). As can be seen in Table 3-V, the intensity of the second overtone v, decreases as the base strength of the solvent increases. 

The phenol molecule has 13 atoms, and is therefore characterized by the 33 normal vibrational modes. Their overtone and combination bands are infrared active. The proper assignment of the fundamental vibrational modes of phenol in its electronic ground state... 

The OH group of phenol participates in two additional modes, in-plane and out-ofplane bending vibrations. The latter is also called the torsional mode toe observed near 300 cm (see Table 8) in the IR spectra of phenol vapour and of dilute solutions of phenol in w-hexane. In the associated molecules, it appears as a rather broad featureless band in the region of 600-740 cm ". It results from the hydrogen-bonded association. The spectra of liquid and solid phenol-OD also exhibit a variety of broad bands near 500 cm . The first overtone of the ton was found at 583 cm in the IR spectrum of phenol vapour. This assignment of the torsional mode allows one to model the torsional motion of the OH group of phenol by assuming that it is described by the... 

The oak aroma becomes more complex as toasting progresses from light to heavy. This aroma is initially characterized by toasty and vanilla overtones from the furanic and phenol aldehydes, as well as smoky, spicy and roasted odors from the volatile phenols. Following heavy toasting, the increase in methyl-octalactones contributes a hint... 

In the polymer industry, packing material, laminates including multilayer films, pellets or molded products can be analyzed by NIR. Even polymer latex particles with up to 99 % water content may be analyzed. NIR provides information about reaction mechanisms, polymerization, crystallinity, orientation, water content and hydrogen bonding, even during the process of polymer manufacture. For example the disappearance of the double bonds in polyethylene and polypropylene can be monitored. In the NIR spectrum C=C bonds lead to a combination band at about 4740 cm and a first overtone at about 6170 cm NIR spectroscopy is applied to characterize ester-, nitrile-, or amide-based acrylic and methacrylic polymers. Other examples are the identification of polyvinylchloride, polyvinyl alcohol and polyvinyl acetates or the analysis of polymerization in epoxy and phenolic resins. 

Two types of PET were used in Overton s study [49] one polymerized in the melt, the other in the solid phase. Molecular mass calibration was achieved using both conventional polystyrene standards and PET fractions, the latter being prepared by precipitation of the polymer from a mixed solvent solution of phenol in tetrachloroethylene by progressive addition of n-hexane. Molecular masses of the fractions were determined by inherent viscosities. 

Knight and coworkers have interpreted their measurements of the bending and stretching of the van der Waals bonds in the (Si) molecules fluorobenzene-Ar, chlorobenzene-Ar, phenol-Ar and aniline-Ar in terms of Fermi resonance between the overtones of the two bending vibrations and the stretching vibration. 

Due to the difference in acidity of phenol relative to simple aliphatic alcohols, its spectra in different solvents are quite different from those of methanol and ethanol. In solvents of low hydrogenbonding capability, phenol shows both free and bonded OH first overtones because the solvent cannot bond the phenol completely. In solvents that are more capable of hydrogen bonding, phenol behaves like the alcohols, except that the sequence is accelerated for example, the spectrum of phenol in N, A-dimethylformamide appears similar to the spectrum of ethanol in pyridine. 

FIGURE 5.5 First overtone of phenol in CCfi (solid curve) and neat orthochlorophenol (dashed). 

Wulf, O.R., Jones, E.J., and Denting, L.S., Combination frequencies associated with the first and second overtones and fundamental OH absorption in phenol and its halogen derivatives, J. Chem. Phys., 8, 753-765, 1940. 

As in amines, the first overtone of OH- and NH-stretching absorptions are comparable in intensity, whereas in the fundamental region the OH is much stronger. A comparison of OH and NH first overtone peak intensities can be seen in Figure 8.6. The figure illustrates the reaction of phenol with an isocyanate to form an amide. 

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