Pyridine ionization potential

Selenolo[2,3-b]pyridine-2-carboxylic acid, 3-hydroxy-synthesis, 4, 1034 Selenolopyridines, 4, 1034—1036 H NMR, 4, 1035, 1036 Selenolo[2,3-c]pyridines synthesis, 4, 1035 Selenolo[3,2-b]pyridines deuteriodeprotonation, 4, 1035 synthesis, 4, 1034 Selenolo[3,2-c]pyridines synthesis, 4, 1035 Selenolo[2,3-b]pyrroles ionization potentials, 4, 1046 Selenolo[3,2-b]pyrroles ionization potentials, 4, 1046 Selenolo[3,4-c]pyrroles non-classical... 

A mixture of water/pyridine appears to be the solvent of choice to aid carbenium ion formation [246]. In the Hofer-Moest reaction the formation of alcohols is optimized by adding alkali bicarbonates, sulfates [39] or perchlorates. In methanol solution the presence of a small amount of sodium perchlorate shifts the decarboxylation totally to the carbenium ion pathway [31]. The structure of the carboxylate can also support non-Kolbe electrolysis. By comparing the products of the electrolysis of different carboxylates with the ionization potentials of the corresponding radicals one can draw the conclusion that alkyl radicals with gas phase ionization potentials smaller than 8 e V should be oxidized to carbenium ions [8 c] in the course of Kolbe electrolysis. This gives some indication in which cases preferential carbenium ion formation or radical dimerization is to be expected. Thus a-alkyl, cycloalkyl [, ... 

A number of correlations of ionization potentials for substituted benzenes (40-42), benzyl (43), phenoxy (44), and alkyl (45) radicals and substituted pyridines (46) with the simple Hammett equation have been reported. Charton (47) has studied the application of the extended Hammett equation to substituted ethylenes and carbonyl compounds. The sets studied here are reported in Table II (sets 2-10 and 2-11). Results of the correlations are set forth in Table 111. The results obtained are much improved by the exclusion of the values for X = C2 H3, Ac, F, H and OAc from set 2-10 (set 2-lOA) and the value for X = H from set 2-11 (set 2-11 A). The composition of the electrical effect corresponds to that found for the Op constants as is shown by the pR values reported in Table IV. 

Nucleophilic Trapping of Radical Cations. To investigate some of the properties of Mh radical cations these intermediates have been generated in two one-electron oxidant systems. The first contains iodine as oxidant and pyridine as nucleophile and solvent (8-10), while the second contains Mn(0Ac) in acetic acid (10,11). Studies with a number of PAH indicate that the formation of pyridinium-PAH or acetoxy-PAH by one-electron oxidation with Mn(0Ac)3 or iodine, respectively, is related to the ionization potential (IP) of the PAH. For PAH with relatively high IP, such as phenanthrene, chrysene, 5-methyl chrysene and dibenz[a,h]anthracene, no reaction occurs with these two oxidant systems. Another important factor influencing the specific reactivity of PAH radical cations with nucleophiles is localization of the positive charge at one or a few carbon atoms in the radical cation. 

Experimental support for the above analysis is found in 2 substituted pyridines where X=CH3 and X=Si(CH3)3. Specifically, the ionization potential of the nitrogen lone pair in the former case is 9—lOeV and 8.5eV in the latter355. ... 

Pyridine has practically the same ionization potential as benzene it does not, however, necessarily follow that the flrst ionization potentials (Table 9) relate to an electron of the highest occupied 7r-orbital. These compounds are bases, though weaker than aliphatic amines, and parallels have been noted between base strength and ease of ionization (Nakajima and Pullman, 1958 Krishna and Chowdhury, 1963), which might indicate that the flrst ionization potential is that of a lone-pair... 

Fio. 18. Linear relationships between the ionization potentials of 4-substituted pyridines and the corresponding substituted benzenes (upper line —O—) and toluenes (lower line —X—). After Basila and Clancy (1963), electron impact data. 

Other experimental evidence leads to essentially the same conclusion regarding the n ionization of pyridine. El Sayed and Kasha (1961) have detected Rydberg series in the absorption spectrum similar to those in benzene and ascribable to n orbitals (9-266 e.v., 02 11-56 e.v., 62) and, in addition, reported a fragmentary series leading to a third ionization potential of 10-3 e.v. which they ascribed to the nitrogen lone pair. Similar values are found by photoelectron spectroscopy which also indicated the 10-3 e.v. (10-54 e.v.) level to be only weakly bonding. 

Figure 18 gives the PE spectrum of pyridine (72HCA255). Hie diagram consists of a plot of electron current incident on the detector in counts per second vs. kinetic energy of these electrons, which is proportional to the ionization potential of the electrons. 

The ionization potentials of several monosubstituted pyrrolo[2,3-3]pyridines, 26, have been calculated by the PM3 method. The values, shown in Table 1, range from 8.43 to 9.71 eV <1997JFA2345>. 

With heterocyclic compounds the determination of the first ionization potential, corresponding to excitation of an electron from the highest occupied 77-molecular orbital, is complicated considerably by the fact that excitation from an n-orbital often precedes that from a 7T-orbital the difference in the energies of these two orbitals is small in the case of pyridine and pyrazine.83 There are two pieces of evidence which indicate that for pyridine-like heterocycles and their aza analogues the excitation in question is from an w-orbital first, the parallelism between ionization potentials and basicities (in agreement with an SCF treatment84-860), and, second, the very small differences... 

Dewar and Maitlis143 discussed quite successfully the course of nitration in series of pyridine-like heterocycles in terms of the Dewar reactivity numbers. There is a continuing interest in the electronic structure of pyridine65, 144-140 a model of this compound has been studied by the ASP MO LCAO SCF (antisymmetrized products) method in the 77-electron approxition.146 The semi-empirical parameters146 were obtained from the most recent values of ionization potentials and electron affinities, and bicentric repulsion integrals were computed theoretically. 

The energy levels corresponding to the second and subsequent ionization potentials of pyridine have been correlated with those in benzene. 

The reliability of semi-empirical methods (AMI, PM3, and MNDO) for the treatment of tautomeric equilibria has been tested for a series of five-membered nitrogen heterocycles, including 1,2,3-triazole and benzotriazole. The known tendency of MNDO to overestimate the stability of heterocycles with two or more adjacent pyridine-like lone pairs is also present in AMI and to a somewhat lesser extent in PM3. Tautomers with a different number of adjacent pyridine-like nitrogens cannot be adequately treated by these semi-empirical methods. Both AMI and PM3 represent major improvements over MNDO in the case of lactam-lactim tautomerism. The stability of N-oxides as compared to N-hydroxy tautomers is overestimated by PM3 method. All three methods give reliable ionization potentials and dipole moments (90ZN(A)1328). 

Iodonium tetrafluoroborate, biphenylene-X-ray structures, 1, 566 Iodopropenylation alkyl halides, 1, 469 Ionenes uses, 1, 289 Ion exchange resins pyridine polymers and, 1, 308-309 Ionization potentials pyridines, 2, 135 cts- 3-Ionol synthesis, 3, 666 cis-/3-Ionone... 

There remains the choice of Up values. As a starting point we have adopted Uc = —9.5 eV, which is known to give satisfactory values for the ionization potentials in hydrocarbons86 and determined U0, Ux, UNH> and t/NHl so as to reproduce the ionization potentials of formaldehyde, pyridine, pyrimidine, pyrrole, and aniline. Moreover,... 

Palmer min (+) CGTO bp pyridine and arsa benzene ionization potentials (/-Orbitals included... 

The comparative ionization potentials of various triazolopyridines and [l,2,3]-thiadiazolo-pyridines versus benzotriazole or benzothiadiazole were determined by electron-impact mass spectrometry (Table 2) <74CS222>. Since their ionization potentials are similar to the benzo-fused analogues, it infers that they have comparable aromaticity profiles. The same technique shows that the [l,2,3]oxadiazolopyridines (9a,b) occur exclusively as the ozy/zo-quinoid-like pyridodiazo-oxide tautomers (Equation (1)). 

Since the suggestion of the sequential QM/MM hybrid method, Canuto, Coutinho and co-authors have applied this method with success in the study of several systems and properties shift of the electronic absorption spectrum of benzene [42], pyrimidine [51] and (3-carotene [47] in several solvents shift of the ortho-betaine in water [52] shift of the electronic absorption and emission spectrum of formaldehyde in water [53] and acetone in water [54] hydrogen interaction energy of pyridine [46] and guanine-cytosine in water [55] differential solvation of phenol and phenoxy radical in different solvents [56,57] hydrated electron [58] dipole polarizability of F in water [59] tautomeric equilibrium of 2-mercaptopyridine in water [60] NMR chemical shifts in liquid water [61] electron affinity and ionization potential of liquid water [62] and liquid ammonia [35] dipole polarizability of atomic liquids [63] etc. 

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