Class III behavior

Fig. 1.4 A proposed mechanism map that distinguishes Class III behavior.

It should be clear that under conditions of very weak coupling, where 2/f < A, AG AGth and Fit Thus, estimates of AGth for a given metal ion and coordination sphere can be derived from the intervalence band energies. Equation (5) also gives the conditions for the boundary between class II and class III behavior, 2/fad =... 

By examining a number of complexes that spanned the range of Class II to Class III behavior, it was possible to show that the properties of the complex, trans,trans-[ Ru(NH3)4(py) 2(//-3)] in acetonitrile can be regarded as benchmarks for delocalization for polyammineruthenium dinuclear complexes incorporating 1,4-dicyanamidobenzene bridging... 

With these caveats in mind, the redox properties of closely related compounds employing the same solvent and counter ion have been very useful - though they cannot alone distinguish between class II and class III behavior on the Robin and Day Scheme [6]. 

It is interesting to note that it is possible to observe a tricritical point+ in binary polar/nonpolar (or quadrupolar/non-polar) systems of the type considered above. Thus if the polar component is a and is Increased, the tricritical point is observed as an Intermediary stage in the transition from class II to class III behavior. This is shown in Figure 6, the tricritical point occurring where the vapor-liquid critical curve, liquid-liquid critical curve, and the liquid-liquid-gas curve meet. (It should be noted that the formation of a tricritical point in this binary mixture does not violate the phase rule, since acts as an additional degree of freedom). 

The Class I binary diagram is the simplest case (see Fig. 6a). The P—T diagram consists of a vapor—pressure curve (soHd line) for each pure component, ending at the pure component critical point. The loci of critical points for the binary mixtures (shown by the dashed curve) are continuous from the critical point of component one, C , to the critical point of component two,Cp . Additional binary mixtures that exhibit Class I behavior are CO2—/ -hexane and CO2—benzene. More compHcated behavior exists for other classes, including the appearance of upper critical solution temperature (UCST) lines, two-phase (Hquid—Hquid) immiscihility lines, and even three-phase (Hquid—Hquid—gas) immiscihility lines. More complete discussions are available (1,4,22). Additional simple binary system examples for Class III include CO2—hexadecane and CO2—H2O Class IV, CO2—nitrobenzene Class V, ethane—/ -propanol and Class VI, H2O—/ -butanol. 

Fig. 6. Qualitative pressure—temperature diagrams depicting critical curves for the six types of phase behaviors for binary systems, where Ca or C corresponds to pure component critical point G, vapor L-, liquid U, upper critical end point and U, lower critical end point. Dashed curves are critical lines or phase boundaries (5). (a) Class I, the Ar—Kr system (b) Class II, the C02—C8H18 system (c) Class III, where the dashed lines A, B, C, and D correspond to the H2-CO, CH4-H2S, He-H2, and He-CH4 system, respectively (d) Class IV, the CH4 C6H16 system (e) Class V, the C2H6 C2H5OH...

Class III Protein solubility is decreased (salting out) and is then increased (salting in) by increasing salt concentration. Except for the soy isolates, there are no other proteins to my knowledge that exhibit this type of solubility behavior. However, in the related polymeriza-... 

It is important to emphasize that the chemical behavior of the successor complex [ArH+, N02 ] in Class II systems is more like that of the pair of free radicals ArH+ and N02. The extent to which the N02 moiety in the successor complex is already bent (i.e. substantially) will further facilitate collapse to the cr-adduct. In this regard, the successor complex in Class II systems is very different from the Class III pre-equilibrium complex [ArH, NO]+, which exhibits ion-radical behavior only upon separation to the free ArH+ and NO species [61]. 

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