Pyrazine symmetrical

The Creutz-Taube anion, [(NH3)5Ru- N(CH=CH)2N Ru(NH3)5] + displays more obvious redox properties, yielding both 4+ and 6- - species, and much interest has focused on the extent to which the pyrazine bridge facilitates electron transfer. A variety of spectroscopic studies supports the view that low-energy electron tunnelling across the bridge delocalizes the charge, making the 5- - ion symmetrical. Other complexes, such as the anion [(CN)5Ru (/z-CN)Ru (CN)5] , are asymmetric... 

Thiazine has been formulated as 1 rather than 2 because it does not form a sulfonamide under Hinsberg conditions. Symmetrical azines can form only one classical monocation, e.g., pyrazine forms 3. The nonclassical cation 4 has been postulated for pyridazine, but there is no compelling evidence in its favor. 

This is first illustrated for the two nonbonding -type orbitals n, and n2 of para-benzyne and pyrazine (Fig. 31). These nonbonding orbitals are derived from outer (2s, 2p) sp2 type hybrids which have not been used in any bonding interaction. Although the overlap between n, and n2 is zero each one overlaps with the central CC bond orbitals. All told, there will arise two distinct molecular orbitals in which nj and n2 enter as combinations (symmetric or antisymmetric) and which have different energies, because of selective interactions with the central bonds. 

Removal of the side chain gives a symmetrical pyrazine (48), best made from a single precursor according to disconnection (a). The side chain can be added by treatment of (48) with the alkyl lithium at the electrophilic centre next to nitrogen (LiH is displacedj. Ana lysis... 

Second-order nonlinear optical waveguide using noncentro-symmetric LB film of pyrazine derivative... 

Figure 1. Quantum-mechanical (thick lines) and mean-field-trajectory (thin lines) calculations obtained for Model 1 describing the S2 — Si internal-conversion process in pyrazine. Shown are the time-dependent population probabilities Pf t) and Pf (t) of the initially prepared adiabatic and diabatic electronic state, respectively, as well as the mean momenta pi (t) and P2 t) of the two totally symmetric modes Vi and V( of the model.

Although Taube s pyrazine Ru"—Ru dimer was produced by the Ag oxidation of [(NHjljRu—NC4H4N—Ru(NH3)5] , attempts to prepare similar Ru"-Ru " complexes from [(NH3)5Ru(C5H4N)2Ru(NH3)5]" and [(NHjljRu—NC5H4C2H4C5H4N—Ru(NH3)5]" were unsuccessful. Cyclic voltammetric data indicated a two-electron oxidation to Ru" -Ru " dimers. In view of the identical ligands around each Ru atom, Mayoh and Day have questioned the localization of the Ru valencies in Taube s dimer into discrete Ru" and Ru " centres. However, a theoretical calculation of the conditions necessary for valence trapping in any mixed valence system, showed that the condition is indeed satisfied by the above Ru compound. Other workers have suggested that the available data on this complex could also be explained by a molecular orbital scheme in which the Ru ion and pyrazine-filled n (or k ) molecular orbitals are mixed, and the unpaired electron is mainly but un-symmetrically shared by the two cations. ... 

The pyrazine ring structure warrants the use of methodology analogous to that of pyridazines for their preparation. Condensation of diaminoethane with 1,2-dicarbonyl compounds 155 provides non-symmetrical pyrazines 156 after aromatization <99SL1203>. 

Replacement of a chloro group on the pyrazine by nucleophilic substitution with the anion of an activated methylene species is the major pathway in the synthesis of pyrrolo[2,3-3]pyrazines. The symmetrical pyrazine 250a undergoes reaction with malononitrile and K2CO3 in acetonitrile to form 251a (Scheme 24). Reaction of this intermediate with benzylamine in acetonitrile affords 252a <2001MC152>. 

A special case, demonstrating the high versatility of the bis-lactimether method , utilizes the symmetrical derivative obtained from L-leucine, i.e, (2S,5S)-2,5-dihydro-3,6-dimethoxy-2,5-bis(2-methylpropyl)pyrazine (1)14. 

The rotational dynamics of nitrogen and carbon dioxide were recorded by Akhmanov and Koroteev [7]. The transients look similar to the transients by Morgen et al. [8], recorded with time resolved Raman induced polarization spectroscopy [9]. A fs-DFWM experiment was performed by Frey et al. [10] on diatomics and linear polyatomics. To prevent collisional dephasing, they transferred the method into the expansion zone of a molecular beam. In succession, experiments on linear molecules and symmetric tops were performed on molecules like CHCI3 [11] and CgHf, [12], Transients of asymmetric tops like the near oblate pyrimidine, pyrazine and pyridine [13] and SO2 [11] were reported in the following years. 

Fig. 17. The emission spectra of pyrazine in benzene at 4.2°K. The upper tracing is fluorescence and the lower one is phosphorescence. Of special interest is the similarity in the activity of totally symmetric vibrations, and the difference in activity for the nontotally symmetric vibrations.

The ion-association phenomena manifested by pyrazine anion-radicals have been studied intensively since the first observation.35 Simple ion-pairs form in ethereal solvents on treatment with alkali metals various structures have been assigned which place the counterion adjacent to one heteroatom or symmetrically above the ring.76 1 16,147-154 Some recent work reinterprets aspects of the earlier material.155-157 Red uction of pyrazine and tetramethy 1-pyrazine by alkali metals in ether solvents in the presence of the metal... 

Owing to its symmetrical structure, pyrazine has, for a given substituent, only one monosubstituted derivative (2-position), three disubstituted derivatives (2,3-, 2,5-, and 2,6-positions), and one trisubstituted derivative (2,3,5-positions). 

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