Pyridine ring, band frequencies

Fig. 4 SERS spectra from A cetylpyridiniumbromide (C,.PyBr) and ce y nmethylamnionouinbromide(C,gTAB)on Agelectrode-surfaces ex situ roughening = -0.2V vs. SCE concentration 10" M in 0.11 1 excitation wavelength at 488 nm 10 mW integration time 1.5 s number of readings 60. pointed a band corresponding to a out of plane mode of the pyridine ring. pointed the bands due to in plane motions of the pyridine ring. The frequencies of the main CH-bands is depicted over both spectra...

The azaindole vNH absorbs quite consistently at 3472 cm in nonpolar solvent, and, because of this high frequency, hydrogenbonding with the pyridine ring nitrogen does not seem to occur. The shift to lower frequency for solid samples is typical of indole vNH, and this band appeared at ca. 3200 cm in Nujol as in KBr. 

The IR spectra exhibited low frequency shifts of absorption maxima in the range 3600-3100 cm" that correspond to hydroxyl stretching vibrations by 130-140 cm and of absorption maxima of C-0 ether stretching vibrations in the py ranose and fura-nose rings at 1200-1100 cm by 19-20 cm". This may indicate formation of intermo-lecular H-bonds between INAH and the polysaccharides. Furthermore, the absorption band at 1750 cm that is typical of carboityl vibrations in the range 1500-1750 cm weakened. An absorption band of medium strength appeared at 1550 cm and was attributed to vibrations of the pyridine ring of INAH. 

One of the most representative evidence of the degradation is the appearance of new spectral bands corresponding to the C=0 vibrations at 1702 cm and 906 cm. Bands reflecting different vibrations of the pyridine ring disappear (857-876, 970-990, and 1479-1490 cm ), reduce the intensity (760-768 cm ), or change the frequency (1580-1586 cm ).[36] Few more spectral responses indicate these changes. For example, when... 

The basicity of the aromatic amine iV-oxide can be substantially varied by the introduction of substituents on the aromatic ring. IR spectra of free N-oxides display a prominent band between 1200 and 1300 cm-1, attributable to the nitrogen-oxygen stretching frequency v(NO). The more activating the substituent, the lower the energy of the absorption. Upon coordination, v(NO) is decreased by up to 60 cm-1. IR data for pyrazole and pyridine derivatives are given in Table 42.281-286... 

In the IR spectra of six-membered heterocycles containing one or more carbonyl groups in the ring (pyridin-2- and -4-ones, the pyrones, and pyrimidones) one of the higher frequency bands in the 1700-1500 cm-1 region can usually be... 

Typical UV spectra of some pyridine V-imines are summarized in Table III. The spectra of the V-imines unsubstituted in the heterocyclic ring contain two transitions near 230 and 320 nm18 which are strongly dependent on the solvent. In addition, ring-substituted compounds show absorption at 270 nm. In the same solvent, the position of the absorption bands is only slightly dependent on the substituent of the imino group, with the exception of the V-arylimines.38 70 71 The azomethine imine system of the V-imines is apparently the essential chromophore since these compounds show analogous absorption frequencies (for a summary of azomethine imines see Timpe.m)... 

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