Molecular orbital calculations, light

Dioxygen activation in transition metal complexes in the light of molecular orbital calculations. R. Boca, Coord. Chem. Rev., 1983, 50,1-72 (245). 

These authors conclude that the problem of internal solvation is still an experimental and theoretical challenge GB measurements for this type of molecules of low volatility are not always in good agreement194. Molecular orbital calculations may help to solve the difficult experimental problems, but they have to take into account conformational isomerisms and the prototropic tautomerisms of the amidine and guanidine moieties. In light of the above discussion, the proton affinities deduced from the experimental GB values should be based on accurate estimations of the entropy of cyclization 86. 

Molecular electronics, class II mixed-valence complexes, 41 303-304 Molecular light switch effect, 43 148 Molecular mechanisms, cobalt(III) hexaamines, 35 119-120 Molecular orbital calculations... 

Fe4C(CO)l3, [HFe4C(CO),2] and [Fe4C(CO)12]2, which are very similar in geometry (see Table I), the carbide resonances are found at 469.8,464.2, and 478.0 ppm. The cause of these large shifts is not yet known, but some light will undoubtedly be shed on this phenomenon by molecular orbital calculations, magnetic suceptibility and temperature-dependent solid-state NMR studies. 

We have shown in this paper that molecular orbital calculations at the ab initio level can be used to predict reliably the spectral transitions in silylenes, to evaluate the effects of substituents on the Si=Si multiple bond, to shed new light on existing experimental data and to direct future work towards the synthesis of novel isomers of disilenes. Although carbon and silicon are isoelectronic, multiple bonds to silicon differ dramatically from multiple bonds to carbon and analogies from carbon chemistry might therefore be entirely misleading when applied to silicon compounds. We believe that our studies have demonstrated the enormous power of modem computational methods and hope that this paper will prompt future theoretical studies and more importantly, theoretical-experimental collaborations in the field of organosilicon chemistry. 

There have been great advances in the study of liquid water by techniques such as X-ray diffraction, far-i.r. absorption, molecular orbital calculation, and computerized molecular dynamics. The didectric relaxation processes in the liquid must now be examined in the light of these advances. 

Although this survey is primarily concerned with the interpretation of the results of molecular orbital calculations, it is apparent that a necessary prerequisite for such a scrutiny is the availability of a sufficiently extensive body of experimental data, with which comparisons may be made and the reliability of other theoretical predictions established. Consequently, it is pertinent here to examine the practical methods by which basic information about the bonding processes in sandwich species may be obtained, and how the ligand field parameters thus derived may shed light on the nature of the metal-ligand interactions. 

Few reports(, 11 ) have been published on the electronicstates of cinnamoyloxy group although there are many of those on the photochemical reactions ). In this paper, the electronic structures in the excited states of cinnamoyloxy group are clarified by the molecular orbital calculations and the spectroscopic procedures, and discussed in connection with the intensity of light absorption, photochemical reaction processes and energy transfers in the sensitization which are important in the comprehensive understanding of the photosensitive polymer. 

In this section we will discuss various reactive intermediates that contain silicon. In particular, the silicon analogues of the classic organic reactive intermediates such as carbenes (silylenes), carbenium (silicenium) ions and carbanions (silyl anions) have attracted the interest of experimentalists and theoreticians. In light of the elusive nature of these species it is not surprising that much of what we know about their properties comes from theory, in particular ab initio molecular orbital calculations. 

Since it appears that some optical absorptions in KN3 are associated with the radicals N4 and possibly NJ, it is of interest to consider the electronic structure of the radicals in order to assign the specific transitions responsible for the optical absorptions. Molecular orbital calculations of the NJ in NaN3 indicated that the ordering of the states in the NJ radical is la, la, 2og, lou, Itt, htg [23]. The transition Itt to litg is allowed and could account for the 565 nm absorption. This transition should be dichroic, with maximum absorption occurring when the E vector of the incident light is parallel to the internuclear axis of the radical. Since the ESR studies of the N2 indicate the radical is parallel to [110], the litu to Ing transition is consistent with the observed dichroic properties of the 565 nm band [69]. 

A theoretical calculation of the force field of (HF)2 has been performed in the light of the structure previously reported for this dimer. Molecular orbital calculations of the structure of solid HF are not in particularly good agreement with that observed experimentally at 4... 

A Knoevenagel condensation/Diels-Alder cycloaddition approach has been developed by Delgado et al. [124]. By infrared light irradiation at 50 °C and solvent-free conditions, the desired products 324/325 were isolated in moderate yields (40-65%), with also moderate to good e t/o-selectivity (Scheme 13.71). Frontier molecular orbital calculations rationalized the stereoselectivity of this process. In the cases of diethyl malonate as the... 

The potential value of the application of molecular orbital methods in colour chemistry is immense. In essence, the reason for this is that the methods enable, in principle, many of the light absorption properties of dyes, from a knowledge of their chemical structure, to be calculated with the aid of a computer. Thus, the colour properties of any dye whose structure may be drawn on paper may be predicted, with some expectation of accuracy, without the need to resort to devising a method for the... 

CCSDTQ (CC singles, doubles, triples, and quadruples) (75-75), CCSDTQP (CC singles, doubles, triples, quadruples, and pentuples) (7P), etc. approaches are far too expensive for routine applications. For example, the full CCSDTQ method requires iterative steps that scale as ( g(/i )is the number of occupied (unoccupied) orbitals in the molecular orbital basis). This scaling restricts the applicability of the CCSDTQ approach to very small systems, consisting of 2 - 3 light atoms described by small basis sets. For comparison, CCSD(T) is an nln procedure in the iterative CCSD steps and an nl procedure in the non-iterative part related to the calculation of the triples (T) correction. In consequence, it is nowadays possible to perform the CCSD(T) calculations for systems with 10-20 atoms. The application of the local correlation formalism (80-82) enabled SchOtz and Werner to extend the applicability of the CCSD(T) approach to systems with 100 atoms (53, 83, 84). 

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