Pyridine spectra

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... 

Fig. 8 A SERS spectra pyridine before (bottom) and after the addition of 1-Br octane in a proportion of 1 5. B SERS spectra from...

MP >260°C, [a]D —40°), which is also a natural product from T. coffeoides (67). Its UV spectrum [ max 227(19200), 260(17700), and 335(13200) in acid solution] indicated a 2-acylindole chromophore perturbed by the presence of a carbonyl group in position 6. Its IR spectrum exhibited two carbonyl absorptions at 1670 and 1615 cm-1 for the carbonyl functions located at positions 3 and 6, respectively, while in the H-NMR spectrum (pyridine-d5) the aromatic proton H-9 was shifted downfield by the neighboring C-6 carbonyl. 

Unit distribution in the substituted PMMA (35) was investigated by two independant methods a) Direct analysis of copolymer microstructure by H-NHR at 250 MHz the NMR spectrum (pyridine solution at 80°C) are sufficiently well resolved to allow a quantitative analysis of unit distribution, in terms of A centered triads and isolated B units in ABA triads, b) UV studies of the ionization and of the intramolecular cyclization of the B B and B B dyads in protic basic media (Na0H-H 0 O.IN, NaOMe-MeOH O.IN) in such a medium the partially ionized copolymer chains are the site of a complex series of consecutive intramolecular reactions we have completely elucidated (35). The first step is of interest with respect to B unit distribution ... 

Pseudoginsenoside-RPi Olennolic acid-3-P-O-O-glucuronopyninosyl (l-2)-p-xylo pyranoside] (2) Colorless needles from methanol, m.p. 230-232°C NMR spectrum (pyridine-ds, 67.8 MHz) was in agreement with that previously published for this saponin (Tanaka c/a/., 1985). 

Still another type of adsorption system is that in which either a proton transfer occurs between the adsorbent site and the adsorbate or a Lewis acid-base type of reaction occurs. An important group of solids having acid sites is that of the various silica-aluminas, widely used as cracking catalysts. The sites center on surface aluminum ions but could be either proton donor (Brpnsted acid) or Lewis acid in type. The type of site can be distinguished by infrared spectroscopy, since an adsorbed base, such as ammonia or pyridine, should be either in the ammonium or pyridinium ion form or in coordinated form. The type of data obtainable is illustrated in Fig. XVIII-20, which shows a portion of the infrared spectrum of pyridine adsorbed on a Mo(IV)-Al203 catalyst. In the presence of some surface water both Lewis and Brpnsted types of adsorbed pyridine are seen, as marked in the figure. Thus the features at 1450 and 1620 cm are attributed to pyridine bound to Lewis acid sites, while those at 1540... 

It was first reported in 1974 that the Raman spectrum of pyridine is enhanced by many orders of magnitude when... 

This bathochromic shift is typical of 77 —> tt transitions. The behavior of the water solution when acidified was attributed by Albert (175) absorption by the thiazolium cation, by analogy with pyridine. However, allowance is made for the very weak basicity of thiazole (pK = 2.52) compared with that of pyridine (pK = 5.2), Ellis and Griffiths (176) consider the differences between the spectrum of thiazole in water and in... 

As in the case of pyridine (185), the quaternization of thiazole induces a bathochromic shift of the ultraviolet absorption spectrum in ethanol the long wavelength maximum at 232.3 nm (3900) for thiazole moves to 240 nm (4200) for 3-methylthiazolium tosylate (186) (Table 1-19). 

The direct coupling constants (A/) of pyridine, obtained from a spectrum of the molecule in a nematic liquid crystal solvent, are listed in Batterham s monograph (B-73NMR, p. lo). These data provide information about the geometry of the molecule, as the couplings are proportional to the inverse cube of the distance (r,/) between the nuclei. 

Pyridin-2-one, 1-hydroxy-fluorescence spectrum, 2, 163 (81XL1515) Pyridin-2-one, 6-methoxy-pK 2, 151 <71JCS(B)289)... 

The //NMR spectrum contains five signals with integral levels in the ratios 1 1 1 1 3 four lie in the shift range appropriate for aromaties or heteroaromaties and the fifth is evidently a methyl group. The large shift values (up to Sh = 9.18, aromaties) and typical coupling constants (8 and 5 Hz) indicate a pyridine ring, which accounts for four out of the total five double-bond equivalents. 

UV spectrum changes dramatically. The salt causes maxima at 251 (4.16), 286 (4.16), 387 (3.56), and 473 (3.37) nm. NMR data for a sample in CF3COOD were presented. It is interesting to note that the nonmethylated derivatives of 130 and 131 are present in solution above pH 6.5 as betaines, forming a protonated pyridine ring and an olate group (91MI3). 

A dicarbocyanine dye, dithiazinine (79), is used as a broad-spectrum anthelmentic agent, although, interestingly, it seems to have been prepared initially for use in photographic emulsions. It is made by heating 2-methylbenzothiazole ethiodide (77) with the malondialdehyde equivalent, B(ethylmercapto)-acrolein diethylacetal (78) in the presence of pyridine. There apparently ensues a sequence of addition-elimination reactions quenching the reaction mixture with potassium iodide solution results in separation of green crystals of dithiazanine iodide (79). ... 

Figure 2. Part of NMR spectrum of 4-0-acetyl-l-0-benzoyl-6-deoxy-2,3 0-isopropylidene-p-n-threohexuloS-enofuranose (48) at 60 Mc.p.s. in pyridine.

From 1,2-0-isopropylidene-3,5-di-0-tosyl-/ -d-xylofuranose (21) (29). Treating 29 with silver fluoride in pyridine and isolating as described above for the l-arabino isomer gave a 40% yield of 32 after a reaction time of 48 hours. The product had [ ]D25 — 14.9° and had an infrared spectrum identical with material prepared as above. 

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