Hydrogen-Bonded Pyridine

From the solvolysis of I-aryl-I-methylethyl chlorides, average o+ values for the hydrogen-bonded molecule are 0.73 (2), 0.51 (3), and 1.16 (4) and these values should apply reasonably well in protic solvents. Any 

---

In general, the solubility of heterocyclic compounds in water (Table 33) is enhanced by the possibility of hydrogen bonding. Pyridine-like nitrogen atoms facilitate this (compare benzene and pyridine). In the same way, oxazole is miscible with water, and isoxazole is very soluble, more so than furan. 

Infrared spectra of pyridine adsorbed on dehydrated TS-1 and Ti-MCM-41 of comparable Ti content indicated the presence of only Lewis acid sites (Fig. 13). The infrared absorptions at 1595 and 1445 cm-1 are attributed to hydrogen-bonded pyridine (Si/Ti-OH—pyridine) and those at 1580 and 1485 cm-1 to pyridine bonded to weak Lewis acid sites (Fig. 12). Brpnsted sites, if present,... 

Figure 3a shows the FTIR spectra characterizing the infrared absorption of pyridine on PSM and AMM samples at room temperature. PSM has two strong absorption peaks at 1447 and 1559 cm"1, which are assigned to hydrogen-bonded pyridine. The FTIR spectrum characterizing the absorption of pyridine on AMM-1 is quite similar to that of PSM. However, when the content of AI2O3 increases to 5 or 10 wt%, some... 

Infrared spectroscopic studies regarding the adsorption of pyridine on both anatase and rutile have been reported (136, 176, 194, 216,217). Hydrogen-bonded pyridine is readily desorbed on pumping at room temperature, whereas pyridine held by coordinatively unsaturated Ti4+ ions is thermally stable up to approximately 400°C. As ammonia, pyridine forms two distinct coordinately held species (176, 217) indicating the existence of two types of Lewis acid sites, which should correspond to Ti4+ ions in different stereochemical environments. According to Primet et al. (176), the more stable species is chemisorbed on type... 

This gas-phase reaction provides the only method currently available for determining free base. The method requires neither assumptions, extrapolations, nor approximations the p factor of the reaction is sufficiently small that the reactivities of the pyridine and benzene derivatives can be compared directly. The method was first introducted for determining the electrophilic reactivity of pyridine [62JCS4881 71JCS(B)2382] using 1-arylethyl acetates (9.109). Subsequent determinations used I-aryl-l-methylethyl acetates. (9.110) and i-arylethyl methyl carbonates (9.111) [79JCS(P2)228],... 

Figure 5. Disappearance of associated silanol sites with desorption of hydrogen-bonded pyridine.

Desorption experiments were carried out at 25°C by introducing an excess amount of pyridine (4 p,l) into the sealed and evacuated DRIFT environmental chamber containing a dry silica dispersion (4 mg sihca) and allowing the system to equilibrate for 30 min. An initial DRIFT spectrum was recorded and the stopcock to a standard vacuum line was opened. Subsequent DRIFT spectra were recorded at various time intervals for 5 hours. Pertinent peak areas of the unassociated silanol band (3740 cm ), hydrogen-bonded pyridine (1445 cm ) band and SiOSi combination band (1870 cm ) were recorded, ratios calculated, and kinetic plots generated for the silanol and pyridine peak area ratios versus time. 

Frutos LM, Markmann A, Sobolewski AL, Domcke W Photoinduced electron and proton transfer in the hydrogen-bonded pyridine-pyrrole system. J Phys Chem B 2007, lll(22) 6l 10-6112. 

Density functional theory study of the hydrogen-bonded pyridine-H20 complex A comparison with RHF and MP2 methods and with experimental data ... 

Yan Y, Gu J, Bocarsly AB (2014) Hydrogen bonded pyridine dimer a possible intermediate in the electrocatalytic reduction of carbon dioxide to methanol. Aerosol Air Qual Res 14 515-521... 

Moisture absorption mechanism at the hydrogen-bonded pyridine ring. 

Hydrogen bonded pyridine Coordinately bonded pyridine Pyridinium ion ... 

---