Rate constant, for diffusion controlled

Note that the rate constant for diffusion controlled reactions between a proton and.a base decreases by a factor of 0.3 to 0.5 for each positive charge added to the base. 

Separation of an ion-pair to free ions, with rate constant d, has been used as a clock for other reactions of the ion pair. Estimates of d can be obtained from the simple relationship between the association constant for ion-pair formation (Xas, equation (2)) and the rate constant for diffusion-controlled encounter... 

Starting with Fick s first law, one can calculate for a solution of two reactants A and B the frequency of A-B encounters, which is in effect the reaction rate constant for diffusion-controlled reactions. This is given by the following, in units of L mol 1 s-1 ... 

Thus, bimolecular rate constant depends only on the viscosity and the temperature of the solvent. The calculated rate constants for diffusion-controlled bimolecular reactions in solution set the upper limit for such reactions. 

This latter equation correctly predicts the rates at which 1-iodo-naphthalene quenches triplet naphthalene in several fairly viscous solvents.165 It also correctly predicts the rate at which 2,5-dimethyl-2,4-hexadiene quenches triplet valerophenone in cyclooctane if the ketone s triplet lifetime is the same as that estimated from quenching experiments and from the flash spectroscopically measured rate constant for diffusion-controlled quenching in benzene.183... 

The extent of catalysis depends critically upon the stability of the intermediate 1. If the rate of expulsion of H20 from 1 (rate constant 7c i) is slower than proton transfer to solvent water, the rate of formation of the intermediate (rate constant ki) will be the rate-limiting step and no catalysis will be observed. The rate constant for protonation of the amine nitrogen of 1 by solvent water, 7cHa (HA = H20), depends on the basicity of the nitrogen and is given by kAKw/Ka, where kA represents the rate constant for diffusion-controlled abstraction of a proton by hydroxide ion, with a value of approximately 1010 M-1 s 1, and... 

Rate constants for diffusion-controlled reactions can be calculated from the laws of diffusion [18, 869]. For a simple cage reaction A -I- B AB, in which A reacts with B every time the two approach one another to within a distance R, the following equation can be derived,... 

The formation of intermolecular complexes in fluid solution requires that after excitation of one of the partners, collision with the other partner must occur within the lifetime of the excited state. Under such circumstances the maximum rate constant for the process is determined by the rate constant for diffusion control in the solvent employed. Furthermore, as the free energy for complex formation decreases, it becomes more and more necessary for multiple collisions to take place if excited complex formation is to occur. To offset unfavourable energetics to some degree, one may resort to creating... 

Table II shows the k and k values obtained. The table shows theoretical rate constants for diffusion-controlled association...

As is known, rate constants for diffusion-controlled reactions can be described by the Debye-Smoluchowski equation ... 

The process of energy transfer requires that the excited donor diffuse to the proximity of an acceptor within the time period of its excited lifetime. This is subject to the viscosity of the medium and the efficiently of the collision process and the range r in which the collisions can occur. The observed rate constant for energy transfer et is governed by the molecular rate constant for diffusion-controlled reaction. This is defined by the Debye equation ... 

Bimolecular association rate constant Rate constant for dissociation Rate constant for Dexter energy transfer Rate constant for diffusion-controlled reactions Rate constant for fluorescence... 

Theory of rate constants for diffusion-controlled reactions... 

For uncharged reactants, the rate constant for diffusion-controlled bimolecular combination (/cd) is given by ... 

It can be seen that Equation 11.4.22 is independent of particle size and all particles and droplets can be pooled in one calculation. The term k2° is the rate constant for diffusion-controlled coagulation. 

---