Processes of homomolecular association

In mixed solvents formed of associated component A and non-associated component B 

The systems alcohol-carbon tetrachloride or carbon acids-cyclohexane are examples of mixed solvents of this type. Interesting examples of sueh mixed solvents are the systems formed of liquid tetraammonium salts, R4NA, and various liquids that are solvate-inert towards sueh eompounds. 

The values of homomolecular association constants of alcohols and acids are high, typieally in the range of 10 -1 O. Therefore eoncentration of the eomponent A is rather low, even at high content of solvate-inert component B, and may be neglected. 

The relative degree of the decomposition of heteromolecular associates into aggregates of a smaller association degree increases with increased permittivity of the non-asso-ciated solvate-inert component. In solutions of equal concentration of the two mixed solvents, acetic acid-cyclohexane (8=1,88) and acetic acid-chlorobenzene (e=5,6), the relative degree of acid heteromolecular association is higher in the first system than in the second system. 

In mixed solvents, formed of two associated components in individual states A , and that do not interact with each other into specific solvation, the chemical equilibrium of mixed heteromolecular associates is established  

---

The systems having components which interact by means of donor-acceptor bond (without proton transfer) belong to the same type of solvents (e.g., pyridine-chloracetyl, dimethylsulfoxide-tetrachloroethylene, etc.). Components of mixed solvents of such type are more or less associated in their individual states. Therefore, processes of heteromolecular association in such solvents occur along with processes of homomolecular association, which tend to decrease heteromolecular associations. 

MIXED SOLVENT EFFECT ON THE POSITION OF EQUILIBRIUM OF HOMOMOLECULAR ASSOCIATION PROCESS... 

All questions this part deals with are considered based on the example of a special and wide-studied type of homomolecular association process, namely, monomer-dimer equilibrium ... 

Mixed solvent effect on the position of equilibrium of homomolecular association process... 

It is emphasized that the terms excimer2 and exciplex3,4 are reserved here for homomolecular and heteromolecular excited double molecules formed after the act of light absorption by one component in a process of photoassociation, in the absence of spectroscopic or cryoscopic evidence for molecular association in the ground state. Recent findings indicate that excimer (or exciplex) formation may also result from triplet-triplet annihilation,5,8 cation-anion combination7 (doublet-doublet-annihilation), and electron capture by the (relatively stable) dimer (or complex) cation8 these processes are discussed in Section VII. 

Type 1 isotherm eorresponds to the experimental isotherm with isotherms [8.1.24] or [8.1.26] of the liquid systems without interaction. The additive e inerease is eompensated by 8 decrease, due to homomolecular association process. The system diethyl ether-m-cresol illustrates this type of isotherm. 

---