Ring vibrations pyridine

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... 

Piperidine has an N—H bond absorbing at 3500 cm and H—C(sp ) stretch below 3000cm. Pyridine has no N—H has H—C(sp ) stretch above 3000cm C=C and C=N stretches near 1600 and 1500cm , respectively aromatic ring vibrations near 1200 and 1050 cm and C—H deformations at 750 cm". The peak at 750 varies with substitution in the pyridine ring. 

The standard preparation of t/ms-[Rhpy4Cl2]+ is due to Delepine,784,785 who noticed that reaction of pyridine with [RhCl6]3- leads to mixtures of [Rhpy3Cl3] isomers, but that in the presence of primary or secondary alcohols, trans-[Rhpy4Cl2]Cl is formed. (The role of the alcohol in this reaction is discussed in more detail in Section 48.6.2.5.iii.) Far IR spectra (pyridine ring vibrations, Rh—N and Rh—Cl stretches) of the fac and mer isomers of [Rhpy3Cl3] confirmed the earlier isomer assignment.786... 

The IR spectrum of poly(vinyl pyrrofidone) (PVP) in Fig. 18 is dominated by the strong C = 0 stretching mode that absorbs between 1,560 and 1,730 cm . Due to molecular interactions the band is broad and asymmetric. The pyridine ring leads to a more complex spectrum. Ring vibrations occur mainly between 1,100 and 1,300 cm. Vibrations of the C-N bond are generally weak for tertiary amines. 

Attempts were made to determine structure by both NMR and IR. The IR spectrum of the copolymer(s) (free film) had absorption bands at 1605 and 755 cm-1 (pyridine ring vibrations), 825 cm 1 (C-H deformation vibration), and 1580 cm 1 (aminimide carbonyl) this supported the structure of poly (DHA-co-4VP). The NMR spectrum showed DHA and 4VP moieties, but the resolution was too poor for quantitative assignments. 

The mass of pyridine remaining adsorbed on the sample at the two (or three) adsorption temperatures, in combination with the integrated areas underneath the bands due to the 19b ring vibrations of pyridine adsorbed at Lewis and Bronsted sites (ca. 1450 and 1540 cm, respectively) at the corresponding temperatures allowed calculation of the Bronsted and Lewis absorption coefficients. The number of Lewis and Bronsted sites could be calculated by fitting this data to the equation (1) ... 

Adsorption of pyridine on Au has also been investigated by Tadjeddine et al. [97, 98]. Here, the advantage of the low-background signal from DFG is used to examine the potential-dependent structure of pyridine on Au electrodes. The ring vibrations at 1008 cm and 1090 cm provide two perpendicular modes (in-plane and out-of-plane) to report on the orientation of the molecule as a function of potential. The pyridine is bonded to the gold through lone pair elec-... 

FIGURE 32.3 DRIFT spectrum of pyridine hydrogen bonded on a dried silica gel surface in the ring vibration region for pyridine. 

Figure 2.4 shows the effect of exposing in to pyridine vapor (-1.3 kPa) at room temperature and at 60°C followed by evacuation at the temperature of exposure. Spectrum 2.4a shows that, at room temperature, intense pyridine bands appeared. The 1441 and 1492 cm bands are the characteristic 19b and 19a ring vibration [25], and the band around 1576 cm- is the 8b ring vibration of all pyridine present... 

Fig. 61. Mazzite with Si/Al = 2.2. (a) IR spectra in the region of the OH stretching vibrations (al) clean surface outgassed at 773 K, (a2) after adsorption/desorption of pyridine at 423 K, (a3) after adsorption/desorption of pyridine at 723 K (au = absorbance unit), (b) IR spectra in the region of ring vibrations after adsorption/desorption of pyridine at 423 K and after adsorption/desorption of pyridine at 723 K. (c) Relative evolution of the intensity of the signals characteristic to Bronsted (circles) and Lewis (crosses) acidity as a function of desorption temperature [96M1].

There is a reasonably close analogy between the ring vibrations of benzene and those of pyridine and quinoline, but there are considerable differences in the hydrogen deformation vibrations. However, the out-of-plane hydrogen deformation vibrations appear to be like those of benzene compounds containing an additional substituent. An a-mono-substituted pyridine, therefore, behaves like an or /20-di-substituted aromatic compound in this respect. Substituted pyridines have been extensively studied in both the Raman and infra-red and correlations are now available which enable the substitution pattern to be recognised. Some more limited data are available on the diazines, pyrazine and pyridazines. 

Frequency of pyridine ring vibration vs temperature upon heating. 

Perflorinated sulfonic acid copolymer EA-4VP copolymer Vinyl pyridine in-plane aromatic ring vibration at 1416 cm decreases, protonated pyridine N band appears at 1642 cm sulfonic acid copolymer = Nafion 300... 

Figure 4.3 Transmission IR spectra of pyridine adsorbed on y-alumina top, MID-IR absorption region bottom, zoom on the ring vibration region, (a) sample before activation (b) activated sample (c) pyridine adsorption and evacuation at room temperature (d) difference between c and b spectra...

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