Theoretical and Quantum Chemical Calculations

Several groups have applied theoretical and quantum chemical calculations to many aspects of the phenanthrolines over the past two decades. The -electron distributions in all the phenanthrolines have been determined, and they are generally in accord with the known chemical reactions of the molecules.37 Resonance energies of 1,7- and 1,10-phenanthrolines have been calculated and compared with those of 7-aminoquinoline and 8-aminoquinoline, respectively.38 Calculations applied to 1,10-phenanthroline and methyl-substituted derivatives have been correlated with their reduction potentials39 and ionization constants.40 Bond lengths for most of the phenanthrolines have been computed.41 

There has been interest in the theoretical treatment of the spectra of the phenanthrolines. Correlations between nuclear magnetic resonance (NMR)42-48 and electronic spectra22,38,40 41,49-51 with various quantum chemical data have been discussed. Often there is reasonable agreement between the calculated and measured spectra. 

Rosenberger, M. Pettig, K. Madeja, G. Engelhardt, and R. Radeglia, Ber. Bunsenges. Phys. Chem. 73, 662 (1969). 

The triplet state of the phenanthrolines has interested several groups, frequently in conjunction with electron paramagnetic resonance (EPR) transitions.22,52-60 Electron spin densities in radical cations and anions of 1,10-phenanthrolines have been calculated.61,62 The binding energies of N-l in salts of 1,10-phenanthroline have been studied using X-ray photoelectron spectroscopy.63 

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There has been considerable interest in theoretical and quantum chemical calculations applied to the bipyridines over the past 25 years. 7i-Electron distributions, electron densities, and molecular orbital calculations on all the bipyridines have been determined, and the results are generally in accord with the known chemical reactions of the molecules.Calculations applied to 2,2 -, 3,3 -, and 4,4 -bipyridines have been correlated with ionization potentials,and reduction potentials ° "and electrical susceptibilities of most of the bipyridines have been determined.The ability of 3,3 - and 4,4 -bipyridines to act as electron-transfer bridges has been calculated. ... 

The Dotz reaction mechanism has received further support from kinetic and theoretical studies. An early kinetic investigation [37] and the observation that the reaction of the metal carbene with the alkyne is supressed in the presence of external carbon monoxide [38] indicated that the rate-determining step is a reversible decarbonylation of the original carbene complex. Additional evidence for the Dotz mechanistic hyphotesis has been provided by extended Hiickel molecular orbital [23, 24] and quantum chemical calculations [25],... 

Carbon monoxide carbo-mers [5-7], i.e., monoxides of linear odd carbon chains longer than one C 0 n = 3, 5, 7, 9...), are highly reactive molecules suggested as potential constituents of interstellar and circumstellar gas clouds. Considerations based on MO theory and quantum chemical calculations indicate that, similar to pure odd carbon chains, all these heterocumulenes are singlet carbenes in the ground state [93]. Since its matrix isolation in 1971 [94] and its synthesis in gas phase in 1983 [95], the simplest member of this family, i.e., tricarbon monoxide C3O, has been extensively studied both experimentally and theoretically [96-102], and its interstellar presence fully confirmed [103]. In particular, on the basis of... 

Tautomeric equilibrium in aqueous cw-malonaldehyde, see reaction 1 in Figure 8-4, is a prototypical reaction extensively studied in the gas phase but still relatively unknown in solution. In fact, despite the large number of NMR experiments [52,53,54] and quantum chemical calculations [55] with the polarized continuum model (PCM), [1] the actual stability of czT-malonaldehyde is not well clarified, although the trans isomer should be the predominant form in water. Secondly, the involvement of the light proton in the reaction may in principle provide relevant quantum effects even in condensed phase. All these complications did not prevent this reaction to be used as a prototypical system for theoretical studies of intramolecular proton transfer in condensed phase by several investigators [56,57,58,59,60] including ourselves. 

In quantum theoretical or quantum chemical calculation of atomic and... 

This problem was intensively studied both experimentally and theoretically. The quantum chemical calculations were carried out using various methods at different levels. The earlier calculations for the Cope reanangement based on a CASSCF wave function for six electrons in the bonds rearranged were found to overestimate the diradical character of the wave funclion- --. More recently, MP2 methods for the multireference wave function have been developed whose application to an estimate of the energy of the chair transition state has been described. AMI calculations of altemative transition states for the Cope rearrangement of 1,5-hexadiene derivatives have been discussed by Dewar and colleagues i -217... 

Summary The conformational equilibrium of the title compound has been investigated experimentally in the gas phase by gas electron diffraction and in solution at low temperatures by NMR, and theoretically by quantum chemical calculations. Both experimental methods result in a preference of the equatorial position of the methyl group, 68(7)% in the gas phase at 298 K and 74(1)% in solution at 110 K. The calculations predict 66 % equatorial conformer at room temperature. 

The details of the theoretical computations (based on MD simulation and quantum chemical calculations) are given in Ungar et al. (1999). The rate constant ( et) was expressed in terms of the results of the computer simulations, using a nonadiabatic TST model (Equation (10)). Since the experimental results were analyzed in terms of a phenomenological Arrhenius model, agreement between experiment (left-hand side) and theory (right-hand side) would yield the following two equations. For the weakly temperature-dependent prefactor we have ... 

The electronic and chemical structure of poly(67) was studied experimentally by X-ray and ultraviolet photoelectron spectroscopy, and theoretically by quantum-chemical calculations [122]. X-ray spectroscopy showed that the thin films were chemically pure with no oxygen present. The remarkably well-resolved S2p spectrum indicated the quality of the polymer material to be excellent (minimum of chemical and spatial... 

According to a large number of experimental studies, the most stable phologen-erated species in the lowest excited stales of conjugated chains are electron-hole pairs bound by Coulomb attraction and associated to a local deformation of the backbone, i.e., polaron-excilons [18]. A good insight into the properties of these species can be provided by quantum-chemical calculations our recent theoretical... 

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