Theoretical studies stability

Pulsed spark sources, in which the material to be analyzed is part of one electrode, are used for semiquantitative analyses. The numerous and complex processes involved in spark discharges have been studied in detail by time- and space-resolved spectroscopy (94). The temperature of d-c arcs, into which the analyte is introduced as an aerosol in a flowing carrier gas, eg, argon, is approximately 10,000 K. Numerous experimental and theoretical studies of stabilized plasma arcs are available (79,95). 

The successful application of heterocyclic compounds in these and many other ways, and their appeal as materials in applied chemistry and in more fundamental and theoretical studies, stems from their very complexity this ensures a virtually limitless series of structurally novel compounds with a wide range of physical, chemical and biological properties, spanning a broad spectrum of reactivity and stability. Another consequence of their varied chemical reactivity, including the possible destruction of the heterocyclic ring, is their increasing use in the synthesis of specifically functionalized non-heterocyclic structures. 

A couple of theoretical studies [5,19] have hitherto attempted to estimate the Peierls transition temperature (Tp) for metallic CNT. A detailed theoretical check with respect to the stability of metallic wavefunction in tube (5, 5) has also... 

Theoretical Studies of Enzymic Reactions Dielectric, Electrostatic and Steric Stabilizations of the Carbonium Ion in the Reaction of Lysozyme A. Warshel and M. Levitt Journal of Molecular Biology 103 (1976) 227-249... 

Theoretical studies of the relative stabilities of tautomers 14a and 14b were carried out mostly at the semiempirical level. AMI and PM3 calculations [98JST(T)249] of the relative stabilities carried out for a series of 4(5)-substituted imidazoles 14 (R = H, R = H, CH3, OH, F, NO2, Ph) are mostly in accord with the conclusion based on the Charton s equation. From the comparison of the electronic spectra of 4(5)-phenylimidazole 14 (R2 = Ph, R = R3 = H) and 2,4(5)-diphenylimidazole 14 (R = R = Ph, R = H) in ethanol with those calculated by using ir-electron PPP method for each of the tautomeric forms, it follows that calculations for type 14a tautomers match the experimentally observed spectra better (86ZC378). The AMI calculations [92JCS(P1)2779] of enthalpies of formation of 4(5)-aminoimidazole 14 (R = NH2, R = R = H) and 4(5)-nitroimidazole 14 (R = NO2, R = R = H) point to tautomers 14a and 14b respectively as being energetically preferred in the gas phase. Both predictions are in disagreement with expectations based on Charton s equation and the data related to basicity measurements (Table III). These inconsistencies may be... 

A theoretical ab initio study of the gas-phase basicities of methyldiazoles (90JA1303) included a discussion of the 4(5)-methylimidazole tautomer-ism. The RHF/4-31G calculations led to the conclusion that the 4-methyl tautomeric form 14a (R = Me, R = R = H) is 5.2 kJ moP more stable than its 5-methyl counterpart 14b. It was emphasized that this result is to be considered as basic-set dependent. However, a recent theoretical study [94JST(T)45] showed that, starting from the RHF/6-31G level, all the more accurate approximations indicate a higher intrinsic stability for the 4-methyl tautomer. At the MP2/6-31G level, the total energy of the 4-methyl tautomer is 0.7 kJ mol lower than that of the 5-methyl tautomer. Inclusion of solvation effects can, thus, strongly affect the position of the tautomeric equilibrium 14a 14b. Recently, a systematic theoretical study... 

The first systematic theoretical study on dihydro-1,2,4-triazines was recently carried out (98JOC5824) the stabilities of all the possible unsubstituted dihydro-1,2,4-triazines were calculated using various theoretical methods, all reliable calculation methods consistently show that the 2,5-dihydro isomer 98 is the most stable. This is in perfect agreement with the experimental observations all the synthetic methods used for the preparation of dihydro-1,2,4-triazines result in 2,5-dihydro isomer 98, provided the structures of the reactants and the reaction mechanism allow its formation. Thus, although Metze and Scherowsky (59CB2481) claimed the formation of 1,2-dihydro-1,2,4-triazine 92 (R = = Ph) in the reduction... 

A wide range of nitroxidcs and derived alkoxyamincs has now been explored for application in NMP. Experimental work and theoretical studies have been carried out to establish structure-property correlations and provide further understanding of the kinetics and mechanism. Important parameters are the value of the activation-deactivation equilibrium constant K and the values of kaa and (Scheme 9.17), the combination disproportionation ratio for the reaction of the nilroxide with Ihe propagating radical (Section 9.3.6.3) and the intrinsic stability of the nitroxide and the alkoxyamine under the polymerization conditions (Section 9.3.6.4). The values of K, k3Cl and ktieact are influenced by several factors.11-1 "7-"9 ... 

Fischer-type carbene complexes, generally characterized by the formula (CO)5M=C(X)R (M=Cr, Mo, W X=7r-donor substitutent, R=alkyl, aryl or unsaturated alkenyl and alkynyl), have been known now for about 40 years. They have been widely used in synthetic reactions [37,51-58] and show a very good reactivity especially in cycloaddition reactions [59-64]. As described above, Fischer-type carbene complexes are characterized by a formal metal-carbon double bond to a low-valent transition metal which is usually stabilized by 7r-acceptor substituents such as CO, PPh3 or Cp. The electronic structure of the metal-carbene bond is of great interest because it determines the reactivity of the complex [65-68]. Several theoretical studies have addressed this problem by means of semiempirical [69-73], Hartree-Fock (HF) [74-79] and post-HF [80-83] calculations and lately also by density functional theory (DFT) calculations [67, 84-94]. Often these studies also compared Fischer-type and... 

The impression that little or nothing is known about emulsion theory and technology, however, is far from the truth. Indeed, a great deal is known— much has been learned from theoretical studies and the Edisonian techniques have made their contributions. In terms of the stability of an emulsion one can predict to a certain extent the effects of radical changes in the types of emulsifier used, changes in pH, addition of certain salts, etc. Qualitatively the effects of changes in viscosity or particle size can also be predicted. 

Theoretical studies that has investigated the homolysis step in different enzymatic systems [68-70] reveal that small models comprising only the corrin ring and two ligands are insufficient and that inclusion of more amino acids are essential to stabilize the radical intermediates. Recently, a QM/MM study of the initial phase of the glutamate mutase-catalyzed reaction found a large electrostatic stabilization by the surrounding protein [70], In our study of MCM we employed the ONIOM QM MM approach to reveal the role of the protein in the rupture of the Co—C5 bond [29],... 

Warshel A, Levitt M (1976) Theoretic studies of enzymic reactions dielectric electrostatic and steric stabilization if the carboniumion in the reaction of lysozyme. J Mol Bio 103 227... 

The theoretical study of complexes [IrLCl], [cpIrCl]1, and [IrChfPIfvh]1, where L is a tridentate chelating ligand, has resulted in the establishment of criteria for selecting tridentate chelating ligands for the stabilization of hydridoalkyl complexes [(Me)Ir(L)(H)Cl].550... 

In the past few years, a large number of experimental and theoretical studies have focused on metal oxide surfaces with the aim of gaining insight into their catalytic, photocatalytic, and gas-sensing activity [68]. Owing to its thermodynamic stability and relatively easy preparation, the rutile Ti02(l 10) surface has evolved into one of the key models for metal oxide surfaces. For example, it has been extensively used in the research of biocompatible materials, gas sensors, and photocatalysts [69]. 

Recently, Schleyer and co-workers reported a theoretical study on the stabilities and geometries of a series of carbonyl type compounds, R2M=0 (M = C, Si, Ge, Sn, Pb R = H, CH3), and those of carbene type isomers [R(RO)M ] as shown in Table II.15 These results show that in (CH3)2 M=0 series the carbene type structure is more stable than the double bond type structure in the case of germanium, tin, and lead, unlike the case of carbon in which the double bond structure is preferred. 

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