Conformational analysis including solvent effects

In a study of the conformational statistics of PS, Yoon, Sundararajan and Flory (YSF) included solvent effects in the analysis [47]. The influence of solvent on conformational energy is important because the distance between chemical groups separated by four bonds is large enough for solvent molecules to penetrate the space between them and provide additional interactions. These results are in complete agreement with the experimental studies of PS conformational structure. For example, YSF found the g rotational states to be insignificant due to severe steric interactions. In addition, the inclusion of solvent effects led to the conclusion that the tt conformation is not the ground state of the meso dyad. 

Examples of the various practical applications of dipole moments include, but are not limited to differentiation between isomers cis and trans, o, m, and p, tautomers, etc ), conformational analysis, studies of molecular geometry, supporting evidence for resonance hybrids, information about the polar character of molecules (important for solubility in different solvents and permeability through membranes), information about electrical effects of substituents (inductive, resonance), studies of hydrogen bonding, and studies of donor-acceptor interactions (e g., charge transfer complexes). Practical cases describing the use of dipole moments for different types of structural studies mentioned above can be found in numerous publications mentioned in this chapter. 

Of the mechanistic issues dealt with in the full study (including kinetic trade-off s between different Co-+ spin states in the reaction product and the role of solvent and conformational fluctuations of the DBA system), we focus here on the activation parameters and related nuclear tunneling and entropy effects which are crucial for establishing meaningful contact with the Arrhenius parameters obtained from the experimental rate data [158]. The theoretical analysis also led to new insights... 

Chemical thermodynamics and kinetics provide the formalism to describe the observed dependencies of chemical-conformational reactions on the external physical state variables temperature, pressure, electric and magnetic fields. In the present account the theoretical foundations for the analysis of electrical-chemical processes are developed on an elementary level. It should be remarked that in most treatments of electric field effects on chemical processes the theoretical expressions are based on the homogeneous-field approximation of the continuum relationship between the total polarization and the electric field strength (Maxwell field). When, however, conversion factors that account for the molecular (inhomogeneous) nature of real systems are given, they are usually only applicable for nonpolar solvents and thus exclude aqueous solutions. Therefore, in the present study, particular emphasis is placed on expressions which relate experimentally observable system properties (such as optical or electrical quantities) with the applied (measured) electric field, and which include applications to aqueous solutions. 

Larger differences were found for the more highly ordered smectic phases, and for ketones bearing substituents which mimic the structure of the mesogen. From an analysis of the results of a number of studies, it was concluded that the effects observed were the result of the solvent s ability to alter the equilibrium constant for trans/ gauche interconversion in favour of the nonquenching tra 5-conformer. These studies included a careful determination of the solubility limits of each solute in the various phases by deuterium nmr spectroscopy and thus also provide several clear examples of the effects and complexities of biphasic solubilization on solute reactivity. 

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