Ring vibrations

The literature concerning the IR spectra of these heterocycles has been extensively surveyed 

Structure of Five-membered Rings with One Heteroatom 

Vibration a Approximate descriptiona c2 Pyrroleh Furan Thiophene Selenophene Tellurophene 

Three (3-CH modes corresponding to in-plane C-H deformations are also observed (Table 19) and are probably best depicted as in (36), (37) and (38), although those for pyrrole will be modified as a result of interaction with the in-plane N-H deformation. The skeletal ring breathing mode (39) 

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TABLE 1-22. NUMBERING AND ACTIVITY OF THIAZOLE RING VIBRATIONS (C SYMMETRY)... 

A" Symmetry Vibrations. The first ring vibration of the A" type has been located at 650 cm as a result of the C-type structure observed for that band (Fig. 1-9) (202,203). 

The second ring vibration gives rise to a very weak infrared absorption band at 467 cm and to a weak and depolarized Raman line at 470 cm (202, 203) (Table 1-23). 

FABLE 1-29. LIMITING FREQUENCIES OF THE VARIOUS RING VIBRATIONS OF THIAZOLE DERIVATIVES... 

Two heterocyclic systems have been investigated - the 1,3,2-dioxaphosphepene (45) and its oxide,13 1,3,2-dioxa-phosphorinanes and their oxides, sulphides and selenides (46).136,137 Three ring vibrations were involved in the conformational study of the amides (46, Y = NR2).137... 

The two strong bands at 1595 and 1472 cm 1 can be assigned to ring vibrations [16 - 18] and a mixed mode containing some additional aromatic CH [16] or aldehydic CH bending [18], respectively. 

There have been many attempts to correlate substituted aromatic species. Among the most successful have been with the I frequency of the C=0 band in (52) and (53), and with the intensity j of the 1600 cm-1 ring vibration in (54) ... 

Zengin et al. [41] characterized a polyaniline (PANI)/MWNT composite. The FTIR spectra of the composite film show benzoid and quinoid ring vibrations at 1500cm-1 and 1600 cm-1, respectively, which indicate the presence of emeraldine salt (ES) of polyaniline. A weak broad band near 3400 cm-1 is assigned to the N—H stretching mode. The strong band at 1150cm-1 is characteristic of PANI conductivity. The FTIR spectrum of PANI/MWNT composite in the ES form exhibits several clear differences from the spectrum of neat ES PANI (1) the composite spectrum shows an inverse... 

Polymer films were produced by surface catalysis on clean Ni(100) and Ni(lll) single crystals in a standard UHV vacuum system H2.131. The surfaces were atomically clean as determined from low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Monomer was adsorbed on the nickel surfaces circa 150 K and reaction was induced by raising the temperature. Surface species were characterized by temperature programmed reaction (TPR), reflection infrared spectroscopy, and AES. Molecular orientations were inferred from the surface dipole selection rule of reflection infrared spectroscopy. The selection rule indicates that only molecular vibrations with a dynamic dipole normal to the surface will be infrared active [14.], thus for aromatic molecules the absence of a C=C stretch or a ring vibration mode indicates the ring must be parallel the surface. 

The AES results indicate that the aniline coverage is more than two times greater than the maximum coverage based on van der Waals radii. The TPR results show this species is too stable to be a condensed multilayer. Hence, we conclude that aniline polymerized forming a very stable polymer layer. In addition, the absence of infrared bands corresponding to C=C stretches or ring vibrations indicated that the poly(aniline) film was formed with the phenyl rings parallel to surface. The infrared results also indicated that the poly(aniline) film had N-H bonds which were oriented perpendicular relative to the surface. 

Pyridine. Pyridine and its methyl substituted derivatives (picolines and lutidines) were found to polymerize electrochemically and, under certain circumstances, catalytically. This behavior was not expected because usually pyridine undergoes electrophilic substitution and addition slowly, behaving like a deactivated benzene ring. The interaction of pyridine with a Ni(100) surface did not indicate any catalytic polymerization. Adsorption of pyridine below 200 K resulted in pyridine adsorbing with the ring parallel to the surface. The infrared spectrum of pyridine adsorbed at 200 K showed no evidence of either ring vibrations or CH stretches (Figure 5). Desorption of molecular pyridine occurred at 250 K, and above 300 K pyridine underwent a... 

Methyl substituents on the pyridine ring had a profound impact on the reactivity of the pyridine ring. 2,6-Lutidine did not react to any appreciable extent on Ni(100) [12]. The infrared spectrum of 2,6-lutidine showed no C=C stretches and ring vibrations, but did show CH... 

Quite a detailed discussion of the IR spectra for 3,5-diazapyrylium salts 93 was published (80ZOB2331). These spectra do not contain ring bands above 1650 cm" . Three or four intense bands at 1640-1540 cm" attributed to aromatic ring vibrations were found. The strong bands at 1460, 1390, 1340, and 1180 cm" were believed to be due to vibrations of C —O and C-N bonds (80ZOB2331 88JHC1023). 

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