Potential-dependent intramolecular

Fast Dyes. Generally, the mechanisms underlying the fast dye responses involve potential-dependent intramolecular rearrangements or small movements of the dye from one chemical environment to another. These... 

The applicability of the reaction-rate formula in the intermediate-friction regime to the interpretation of conformational changes of bi-naphtyl in solution has been discussed.47 The intramolecular motion is governed by a bistable potential depending on a single variable, which is identified with the dihedral angle between the naphthalene moieties in binaphtyl. The influence of hydrodynamic interactions and coupling with the other coordinates of the molecules also are evoked. 

Ever since the first in situ Infrared spectral measurements of CO adsorbed on metal electrodes, the experimentally observed potential dependence of the vibrations of CO in its chemisorbed state has attracted much attention. This concerns both the intramolecular C-0 stretch and the metal-adsorbate M-CO vibration. Because of the great significance of this system to electrochemical surface science, a separate section devoted to the field-dependent chemisorption of CO on (transition-) metal electrodes is warranted. This is also the electrochemical system that has served as a paradigm for the application of quantum-chemical techniques to field-dependent electrochemistry, starting with the semi-empirical work of Anderson and the ab initio Hariree-Fock based calculations of Bagus and coworkers. ... 

It should be noted that we have taken the faction coefiiaent C and the spring constant H to be mdependent of the temperature, and therefore the time constant Ajj is temperature independent. Although it might be appropnate to take into account the variation of the time constant with temperature, it does not seem to be possible to do so in the present formulation of the kmetic theory, because of the assumption made in Eq. (2.24) that the intramolecular potential depends only on the interbead distances and not on the position in space or on the time. Allowing H to be a function of T i,t) would be in violation of the assumption in Eq. (2.24) Numerous papers have appeared in the literature in which H IS taken to be temperature-dependent, and we question the correctness of the results. 

Summary A series of chiral zwitterionic monocyclic A, 5i-silicates with an 5 r02C2F framework have been synthesized and characterized. Various time- and temperature-dependent solution-state NMR experiments have been performed to distinguish between different potential mechanisms (intramolecular isomerization and intermolecular ligand exchange) that could change the absolute configuration of the chiral trigonal-bipyramidal A, 5(-silicate skeleton of the title compounds. 

DFT). As a consequence of the fractional oxidation-state situation corresponding to an 18 -I- 5 valence electron count, we can expect a potential to adopt unusual metal configurations through electron-transfer-dependent intramolecular coordination, accompanied by intermolecular reactivity enhancement toward small molecule activation. 

Following the classical approach of vibrational dynamics (as in the case of o--bonded polymers) [67], the experimental data from the oligomers could in principle be used to obtain the phonon dispersion curves of the ideally infinite polymer. In the case of 7r-bonded systems, complications arise because the skeletal modes are strongly CL-dependent and cannot be treated in the standard way. The rationalization of the behavior of the totally symmetric Raman-active normal modes leads to the definition of a CL-dependent intramolecular potential on which the effective conjugation coordinate (ECO theory is based (see Section IV). 

It is then reasonable to think that changes in the intramolecular potential related to changes of the 7r-electron distribution take place mainly when the R coordinate is activated. It then becomes possible to give a simplified description of the CL-dependent intramolecular potential a common potential for polyenes of any length and trans-PA was determined where all force constants but Ff, were kept fixed for all molecules. Fj, represents the effective diagonal force constant relative to the R coordinate it can be written as a linear combination of the more familiar valence force constants relative to carbon-carbon bond. stretching coordinates, according to the expression... 

The relative importance of the potential catalytic mechanisms depends on pH, which also determines the concentration of the other participating species such as water, hydronium ion, and hydroxide ion. At low pH, the general acid catalysis mechanism dominates, and comparison with analogous systems in which the intramolecular proton transfer is not available suggests that the intramolecular catalysis results in a 25- to 100-fold rate enhancement At neutral pH, the intramolecular general base catalysis mechanism begins to operate. It is estimated that the catalytic effect for this mechanism is a factor of about 10. Although the nucleophilic catalysis mechanism was not observed in the parent compound, it occurred in certain substituted derivatives. 

Next come the dihedral angles (or torsions), and the contribution that each makes to the total intramolecular potential energy depends on the local symmetry. We distinguish between torsion where full internal rotation is chemically possible, and torsion where we would not normally expect full rotation. Full rotation about the C-C bond in ethane is normal behaviour at room temperature (although 1 have yet to tell you why), and the two CH3 groups would clearly need a threefold potential, such as... 

Intramolecular Isotope Effects. The data in Figure 2 clearly illustrate the failure of the experimental results in following the predicted velocity dependence of the Langevin cross-section. The remark has been frequently made that in the reactions of complex ions with molecules, hydrocarbon systems etc., experimental cross-sections correlate better with an E l than E 112 dependence on reactant ion kinetic energy (14, 24). This energy dependence of reaction presents a fundamental problem with respect to the nature of the ion-molecule interaction potential. So far no theory has been proposed which quantitatively predicts the E l dependence, and under these circumstances interpreting the experiment in these terms is questionable. 

The pressure dependence of wavenumbers has been investigated theoretically by LD methods on the basis of a Buckingham 6-exp potential. In the studies of Pawley and Mika [140] and Dows [111] the molecules were treated as rigid bodies in order to obtain the external modes as a function of pressure. Kurittu also studied the external and internal modes [141] using his deformable molecule model [116]. The force constants of the intramolecular potential (modified UBFF) were obtained by fitting to the experimental wavenumbers. The results of these studies are in qualitative agreement with the experimental findings. 

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