Protonation theoretical aspects

Some theoretical aspects of thiophene reactivity and structure have also been discussed, for example the kinetics of proton transfer from 2,3-dihydrobenzo[6]thiophenc-2-onc <06JOC8203>, the configuration of imines derived from thiophenecarbaldehydes <06JOC7165>, and the relative stability of benzo[c]thiophene <06T12204>. The kinetics of nucleophilic aromatic substitution of some 2-substituted-5-nitrothiophenes in room temperature ionic liquids have also been investigated <06JOC5144>. 

Most of the AIMD simulations described in the literature have assumed that Newtonian dynamics was sufficient for the nuclei. While this is often justified, there are important cases where the quantum mechanical nature of the nuclei is crucial for even a qualitative understanding. For example, tunneling is intrinsically quantum mechanical and can be important in chemistry involving proton transfer. A second area where nuclei must be described quantum mechanically is when the BOA breaks down, as is always the case when multiple coupled electronic states participate in chemistry. In particular, photochemical processes are often dominated by conical intersections [14,15], where two electronic states are exactly degenerate and the BOA fails. In this chapter, we discuss our recent development of the ab initio multiple spawning (AIMS) method which solves the elecronic and nuclear Schrodinger equations simultaneously this makes AIMD approaches applicable for problems where quantum mechanical effects of both electrons and nuclei are important. We present an overview of what has been achieved, and make a special effort to point out areas where further improvements can be made. Theoretical aspects of the AIMS method are... 

Apart from the obvious use of proton NMR spectroscopy as an aid in structure elucidation, the technique has also been used to probe the phenomena of intermolecular aggregation, apical ligand binding, NH tautomerism, rates of protonation, and a host of theoretical aspects. An extensive review of porphyrin and chlorin NMR spectroscopy has appeared... 

Photochemistry of protonated Schiff bases is also based on conical intersections however, the excited state is ionic and corresponds to an intramolecular charge transfer state thus the theoretical aspects of the problem are distinct from polyenes. 

Theoretical Aspects of Proton Transfer Reactions in a Polar Environment... 

Charged particles. For protons and deuterons, the response of the scintillator is proportional to the particle energy, at least for > 1 MeV. For alpha particles, the proportionality begins at about 15 MeV (Fig. 6.9). Theoretical aspects of the response have been studied extensively. Today, inorganic scintillators are seldom used for detection of charged particles. 

By accident, almost all the nuclei of interest to the vast majority of chemists have spins 7=1/2 and hence do not differ at all from protons in their basic theoretical aspects. However, their usefulness does not warrant the effort of learning any empirical parameters relating to them, so the remarks below do not reflect the amount of data available. 

M.L. Di Vona, E. Sgreccia, S. Tosto, Diffusion in solid proton conductors theoretical aspects and nuclear magnetic resonance analysis, in P. Knauth, M.L. Di Vona (Eds.), Solid State Proton Conductors Properties and Applications in Fuel Cells, John Wiley Sons, Ltd, Chichester, 2012, pp. 25—70. 

The theoretical study by Torrent et al. led to a mechanistic energy profile that seems inconsistent with a first-order dependence of the rate on the pressure of CO. This and other theoretical aspects are discussed in a review by the same authors. The classic mechanism involves attack of OH on coordinated CO to give M—C02H , which is protonated by HjO and loses COj to form MCHjj. Then, H2 is reductively eliminated, and CO added to return the catalyst. More recently, a theoretical analysis of the alkaline Fe(CO)j system by Barrows has led to the mechanism shown in Scheme 5.47. In this Scheme, the species in braces show the composition... 

Others have defined physical chemistry as that field of science that applies the laws of physics to elucidate the properties of chemical substances and clarify the characteristics of chemical phenomena. The term physical chemistry is usually applied to the study of the physical properties of substances, such as vapor pressure, surface tension, viscosity, refractive index, density, and crystallography, as well as to the study of the so-called classical aspects of the behavior of chemical systems, such as thermal properties, equilibria, rates of reactions, mechanisms of reactions, and ionization phenomena. In its more theoretical aspects, physical chemistry attempts to explain spectral properties of substances in terms of fundamental quantum theory, the interaction of energy with matter, the nature of chemical bonding, the relationships correlating the number of energy states of electrons in atoms and molecules with the observable properties shown by these systems, and the electrical, thermal, and mechanical effects of individual electrons and protons on solids and liquids. ... 

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