Behavior Of Pyridine Research Articles

ChemInform Abstract: A Computational Analysis of the Structural Features and Reactive Behavior of Some Heterocyclic Aromatic N-Oxides

Abstract An ab initio self-consistent-field molecular orbital analysis of the structural features and reactive behavior of pyridine, pyrazine and some of their N -oxide and nitro derivatives has been carried out. Optimized structures have been computed at the 6-31G ∗ level, yielding geometries in good agreement with experiment. These structures have been used to compute STO-5G electrostatic potentials and average local ionization energies on the respective molecular surfaces. There is considerable conjugation between the N -oxide groups and the aromatic rings, leading to significant para -quinonoid influence, manifested both in terms of structures and reactive properties. The charge-donor role of the N -oxide group allows the aromatic ring in pyridine N -oxide to be susceptible to electrophiles (at the para position) as well as nucleophiles; however, the rings in the pyrazine oxides are only receptive to the latter. The local ionization energies have permitted predictions of pK a values for pyrazine N -oxide and p -nitropyridine.

Synthesis and metal extraction behavior of pyridine and 1,2,4-triazole substituted calix[4]arenes

Three series of heterocycle substituted calixarenes, derivatized at lower and upper rim, were synthesized and successfully evaluated for metal extraction towards alkali, alkaline, transition and heavy metal ions. The presence and placement of sulfur, heterocycle functionality at upper/lower rim played a crucial role toward the extractability and selectivity of metal ions. The lower rim substituted calixarenes have shown high extractability and poor selectivity. In contrast to this, upper rim substituted calixarenes exhibited good selectivity. Moreover, sulfur functionalized calixarenes have shown better selectivity for heavy metal ions than alkali and alkaline metal ions. Among upper rim substituted calixarenes, 17 and 18 were found to be suitable for Na+, K+ and Ag+, 19,13 for heavy metal ions i.e., Pb2+, Hg+, Hg2+ and Ag+, and 11,12 for Pb2+ and Ag+ only.

Piano-Stool Iron(II) Complexes as Probes for the Bonding of N-Heterocyclic Carbenes: Indications for π-Acceptor Ability

A series of new piano-stool iron(II) complexes comprising mono- and bidentate chelating N-heterocyclic carbene ligands [Fe(cp)(CO)(NHC)(L)]X have been prepared and analyzed by spectroscopic, electrochemical, crystallographic, and theoretical methods. Selectively substituting the L site with a series of ligands going from carbene to pyridine to CO suggests that CO is the strongest π acceptor, while the behavior of pyridine and carbene is nearly identical. This suggests that in these complexes comprising an electron-rich iron(cp)(carbene) fragment, N-heterocyclic carbenes are not pure σ donors but also moderate π acceptors. Theoretical calculations support this bonding model and indicate charge saturation at the metal as key for π back-bonding to N-heterocyclic carbenes. On the basis of voltammetric measurements, the Lever electrochemical parameter of these carbenes has been determined: EL = +0.29. Systematic substitution of the wingtip groups of the carbene revealed only subtle changes in the electronic p...

Development of techniques for purification of waste waters: removal of pyridine from aqueous solution by adsorption at high-area C-cloth electrodes using in situ optical spectrometry

The adsorption and electrosorption/desorption behavior of pyridine (Py) was studied for potential applications to the purification of industrial waste-waters. The use of high-area carbon cloth (C-cloth) electrodes as quasi-3-dimensional interfaces, coupled with in situ UV–Vis spectrophotometric techniques and scanning kinetics for quantitatively monitoring the adsorption/desorption processes and simultaneously obtaining kinetic parameters are described. The conversion of Py to PyH +, which decreases the removal efficiency, takes place in non-buffered electrolyte solution due to pH changes but is eliminated in a HOAc+NaOAc buffer (pH 6.8) solution. Rapid and complete removal of Py is then achieved by anodic polarization. Under controlled potential, Py removal rates are lower than those for galvanostatic polarization where changes of potential arise due to double-layer charging.

ChemInform Abstract: Electron Energy Loss and Thermal Desorption Spectroscopy of Pyridine Adsorbed on Pt(111).

The chemisorption behavior of pyridine (NC/sub 5/H/sub 5/) on a Pt(111) surface has been examined by using thermal desorption and electron energy loss spectroscopy as a function of adsorption temperature. The vibrational spectrum of pyridine adsorbed to room temperature on this surface shows intense loss peaks in the specular direction from vibrational modes which can be characterized as in-plane stretching and bending modes. This vibrational spectrum has been interpreted as the formation of an ..cap alpha..-pyridyl species (NC/sub 5/H/sub 4/) on the surface. The pyridyl moiety is bonded to the platinum surface through the nitrogen and one of the ..cap alpha..-carbon atoms with the pyridyl plane perpendicular to the metal surface. When pyridine is adsorbed at low temperature (120 K), it bonds to the surface through both the nitrogen atom and the ..pi.. and ..pi../sup */ orbitals of the pyridine ring. As the crystal is warmed to 260 K, at saturation coverage, approximately 50% of the molecules desorb as molecular pyridine. The remaining pyridine molecules partially decompose on the surface to form an ..cap alpha..-pyridyl fragment. The electron energy loss spectra of pyridine adsorbed at both low and room temperature is compared to the infrared spectra of two osmium clustermore » compounds: Os/sub 3/(CO)/sub 11/(NC/sub 5/H/sub 5/), a pyridine complex, and HOs/sub 3/(CO)/sup 18/NC/sub 5/H/sub 4/), a pyridyl complex.« less

The behavior of pyridine, pyridinium ion, and pyridinium halide on a silver electrode and their SERS spectra

Resultats d'etudes par diffusion Raman augmentee en surface des especes adsorbees sur l'electrode. On montre qu'en solution neutre ou basique les especes adsorbees sur l'electrode correspondent a la pyridine. En solution acide, exempte d'ions chlorure, l'ion pyridinium se transforme en pyridine sur l'electrode, tandis qu'en presence de chlorures il y a coadsorption d'ions pyridinium et chlorure avec formation de chlorure de pyridinium

Efficient gold and silver electrodes for surface enchanced raman spectral studies of electrochemical systems: The behaviour of pyridine and naphthalene adsorbed on roughened gold electrodes

A method is described whereby surface enhanced Raman (SER) active electrode surfaces of gold and silver may be made without recourse to the oxidation—reduction techniques which have been used hitherto. This method involves electroplating at low current density from dilute (< 10 −2 M) solutions of a suitable salt or complex in the absence of supporting electrolyte. Scanning electron microscopy shows the surfaces to consist of small spherical particles of fairly constant diameter packed together on the electrode. The sphere diameters are typically 70 nm (gold) and 180 nm (silver) for electrodes prepared in this manner. These electrodes exhibit intense SER scattering and have advantages over oxidation—reduction roughened electrodes. As examples of their utility some results are presented relating to the gold/pyridine and gold/naphthalene systems and these are discussed in relation to results obtained by other workers in similar systems using different methods, i.e., ellipsometry and differential capacitance variation.

An examination by mass spectrometry of the behaviour of pyridine, some methyl-substituted pyridines and tetracyanoethylene on a hot tungsten filament

An examination is made by mass spectrometry of the negative ions formed when pyridine and methyl-substituted pyridines flow over a heated tungsten filament. For each substrate a small fraction (5-10%) of the negative ions have masses one unit less than the substrate. The relative amounts of these and other ions formed do not vary with filament temperature. Results are interpreted in terms of the formation of a precursor ion and appear to justify the magnetron technique in which the temperature dependence of total negative ion currents is used to determine electron affinities. In previous work with the magnetron (Failes etall973,1976) the technique of Page has been used to study negative ions formed by pyridine and methyl-substituted pyridines on a heated tungsten filament. In this technique the dependence of the ion current on the filament temperature is related to the electron affinity of the charge-carrying species. The magnetron method, however, is non-specific and deductions made about the identity of charge carriers on energetic grounds may be in error. A re-examination by mass spectrometry of the negative ions formed has therefore been undertaken. The results show that provided the mechanism of the rate determin- ing process has been established the magnetron method may be used to give a valid measure of the electron affinity.

Nuclear relaxation and motional anisotropy of liquids-triazine

The dynamic structure of liquid s-triazine has been studied by analysing the deuterium and nitrogen-14 quadrupolar relaxation data of d 3-s-triazine. The molecular motions are markedly anisotropic with: (a) fast, large angle jump, inertial type in-plane motions of almost zero activation enthalpy and large negative activation entropy; (b) comparatively slow, small angle jump, rotational diffusion type, out of plane motions of higher activation enthalpy and small activation entropy. Comparison of the data on the dynamic behaviour of pyridine [3] and benzene [4] with the present ones on s-triazine leads to a general picture of molecular motions of planar hexagonal rotors in the liquid state (at atmospheric pressure). The behaviour of pyridine, which has a dipole moment departs somewhat from the more similar (and more anisotropic) behaviour of benzene and s-triazine. These results also support our previous finding of motional anisotropy in liquid pyridine [3]. A pictorial representation of the motional anisot...

The electrochemical behavior of pyridine

1. In the reduction of pyridine on a mercury dropping electrode, along with the catalytically evolved hydrogen there occurs reduction of pyridine with formation of a surface active polymeric product. 2. The increase in catalytic wave in pyridlne solutions with time depends on the catalytic action of the polymeric product which accumulates on the surface.