Dissociative structures

The second illustration indicates that less energy is required to dissociate structures with both cavities filled, than those with one cavity filled. Tse (1994) suggests that collisions of a guest with the cavity wall weakens interactions between the hydrogen bonds, which is also reflected in a high value of thermal expansion. 

In this section, the stable physisorbed configurations of the 1-propanol molecule on the Si(001)-(2 x 1) surface are described for a coverage level of 0.125 ML, where three non-dissociative structures are identified. Then seven possible dissociated structures are considered which correspond to chemisorbed configurations. From... 

The method was applied to nucleophilic substitution on NAD+, including hydrolysis and ADP-ribolization reactions of peptide substrates. It was shown that in these systems the hydrolytic TS s follow Sn2 mechanisms with highly dissociative structure. In the TSs the ADP-ribosyl bond is completely broken with low but significant bonding to the water nucleophile. 

Traditionally, the initial purification step after extraction of plant tissues has involved partitioning between an aqueous phase and an immiscible organic solvent. Neutral compounds are distributed between the two phases according to their partition coefficient d = C org/Caq- The distribution of ionizable molecules, however, depends upon their and the pH of the aqueous phase and they migrate into the organic phase when they are in an uncharged form. Amphoteric compounds tend to remain in the aqueous phase because they exist as dissociated structures regardless of pH [49],... 

Rudolph, W. and Steger, W. (1991) Dissociation, structure, and rapid proton exchange of phosphoric acid in dilute aqueous solutions. V. Vibrational spectra of phosphoric acid. Z. Phys. Chem., 172 (1), 49-59. 

The saddle points were obtained as the superposition of the surfaces obtained by starting from the CASSCF wavefunction of the linear structure and the CASSCF wavefunction of the dissociated structure (Y -l-Hj). The barrier height of the A surface (0.98 eV) is lower than the corresponding values of (2.09 eV) and (1.41 eV) states. 

Regarding ethanol oxidation, studies of thermochemical oxidative ethanol dehydrogenation at 303 K revealed structure sensitivity for Pt particle sizes lower than 2 mn. The turnover frequency decreased by a factor of two when the particle size decreased from 2 nm to 1.5 nm [233]. In the case of electrocatalytic ethanol oxidation the experimental evidence is less clear. However, due to the nature of the reaction, involving potentially C-C bond dissociation, structure sensitivity is expected to occur. More studies are required, aimed at clarifying the structure sensitivity of ethanol electrooxidation. 

Hence, in contrast to previous DFT calculations the hybrid HF-DFT functional leads to stable molecular adsorption on this surface. Starting with the broken water molecules, a stable dissociated structure has been obtained where hydroxyls were attached to fivefold tin and protons were bonded to the bridging oxygens (Fig. 11.17b). The energy of the hydrolyzed structure is lower by about 35 kJ/mol than the energy of the molecular structure (see Table 11.19). It is difficult to compare directly these... 

The formulation of the pyrrole Grignard reagents as ionic, but not highly dissociated, structures related to (104) enables the predominant C-substi-tution reactions to be formulated in the same way as the similar processes leading to C-substitution in the alkenylation of other metallic derivatives of pyrrole (p. 67). The reagents should be regarded as sources of more or less dissociated ambident pyrrole anions (p. 68). 

Figure 10.2 Schematic describing the morphology of TPU (a) phase-separated morphology below the glass transition temperature (Tgij) of the hard segments and (b) mostly dissociated structures above the melting point (rjjjjj) of the hard segments. (Reprinted from Lee et al., Macmmolecules 20 2089. Copyright 1987, with permission from the American Chemical Society.)...

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