Two-step dissociation

The poly(methyl methacrylate)s prepared in this experiment, as well as polymers formed in model reactions with silanes that contain bulky substituents (such as phenyldimethyl and diphenylmethyl groups), have predominantly syndiotactic structures identical to polymers prepared by the conventional group-transfer process. This result supports a two-step dissociative mechanism for a group-transfer process, because steric hindrance from bulky silyl groups should increase the proportion of isotactic triads in the hypothetical associative concerted propagation step. 

First, the two-step dissociation of catechol must be considered ... 

J The only mechanism that generates a theoretical rate equation that is first-order is a two-step dissociative mechanism with the first step rate-limiting. 

Already, many years before titanium-doped NaAlH4 was recognized as a possible hydrogen storage medium [152], Dymova et al. [153,154] showed that the two-step dissociation of NaAlH4 into NaH, Al and hydrogen (Eq. (6.14)) is in fact reversible. However, due to the poor kinetics of the uncatalyzed system, the reverse reaction requires unpractically severe reaction conditions (200 00 °C, that is, above the 183 °C melting point of the tetrahydride, and 100-400 bar). 

The corrosion of iron in the presence of hydrogen snlfide and water is dependent on the dissociation of the hydrogen-sulfide molecule. Iron is oxidized to the ferrons form at the anode, and hydrogen sulfide undergoes a two-step dissociation at the cathode. Tung et al. (2001) propose the following equilibrium reactions. 

The potentiometric titration curves of HA are usually broad and ill-defined, reflecting the varying properties of acidic groups on HA [23,24]. Wilson and Kinney [25] investigated the acid-base properties of lake water and marine humic substances and determined a two-step dissociation process. Schnitzer and... 

Fig. 1.21 Feynman diagram of DP-CP energy transfer from a fiber probe tip to a molecule, (a) and (b) show single-step and two-step dissociations, respectively...

Fig. 6.18 Two-step dissociation of nitrilo guests with Xtren-Cu cranplexes...

The clouds and fog droplets are acidified by the uptake of SO2 and other acidic species. Before discussing this, let us discuss the pH of water droplets by CO2 in the atmosphere. The CO2 molecule dissolved into water dissociates to bicarbonate ion, HC03, and carbonate ion, COs, after forming a molecular complex between H2O molecule, C02 H20, by two step dissociation,... 

Fig. 11.3 (a) Energy-level diagram and vibrational transitions for the two-step dissociation of NH3. (b) Spectral lines for normal (dashed lines) and laser-excited (solid Unes) NH3. 

All these polymers display a poly-a-amino acid structure. Their polyampholytic behavior has been examined from the point of view of their two step dissociation constants, and their complexing properties towards bivalent metal ions. 

Iron is oxidized to the ferrous form at the anode and hydrogen sulfide undergoes a two-step dissociation at the cathode as shown below. 

Fig. 11.22 Calculated energetics of the two-step dissociation of CD3OH on the rutile Ti02(l 10) surface. The structures shown are simplified schematics (Modified with permission from Ref [171]. Copyright 2012 American Chemical Society)...

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