Contact charge-transfer complexes

The ethylenediamine derivative [31] possesses higher promoting activities than other diamines. This phenomenon may be ascribed to the copromoting effect of the two amino groups on the decomposition of persulfate through a CCT (contact charge transfer complex) formation. So we proposed the initiation mechanism via CCT as the intimate ion pair and deprotonation via CTS (cyclic transition state) as follows ... 

This association has its counterpart that was also variously described as an encounter complex, a nonbonded electron donor-acceptor (EDA) complex, a precursor complex, and a contact charge-transfer complex.10 For electrically charged species such as anion/cation pairs (which are relevant to ion-pair annihilation), the pre-equilibrium association results in contact ion pairs (CIP)7 (equation 3)... 

A relatively strong organization of an electron donor by an acceptor is typically indicated by experimental values of KEUA or KC f> > 10 M-1. For intermediate values of the formation constant, i.e., 1 < KE A < 10 m, the donor/acceptor organization is considered to be weak.17 Finally, at the limit of very weak donor/acceptor organizations with KEDA 1, the lifetime of the EDA complex can be on the order of a molecular collision these are referred to as contact charge-transfer complexes.18... 

Onodera, K., Furusawa, C.-I., Kojima, M., Tsuchiya, M., Aihara, S., Akaba, R., Sakuragi, H. and Tokumaru, K. (1985). Mechanistic considerations on photoreaction of organic compounds via excitation of contact charge transfer complexes with oxygen. 

Takeya, H., Kuriyama, Y. and Kojima, M. (1998). Photooxygenation of stilbenes in zeolite by excitation of their contact charge transfer complexes with oxygen. Tetrahedron Lett. 39, 5967-5970... 

Fig. 4. Contact charge transfer complexes of nitrobenzene with VCZ and poly VCZ measurements of optical density at 437 mp. at room temperature Optical length 1 cm VCZ, -o- Poly VCZ in nitrobenzene, [NB] + [VCZ] = 0.3 M in benzene...

Fig. 6. Contact charge transfer complex between IBVE and AN. [IBVE] -f- [AN] = 0.3 M. Optical length 0.1 cm. Solvent n-hexane, O.D./[AN] = ey[IBVE]...

The earlier sections have described the evidence for relaxed and non-relaxed exciplexes giving rise to full electron transfer with the formation of solvated radical ions. With many systems, the possibility exists for electron transfer to occur without prior formation of a contact charge-transfer complex if a solvent of sufficiently high polarity is used such is the case for [41]. The intramolecular radical ion of [41] in acetonitrile has a relative short lifetime ( 30 nsec) and this illustrates the point that to obtain stable reaction products via electron-transfer reactions (28) one has to overcome the important back electron-transfer reaction (28b). 

Irradiation of the contact charge transfer complex formed between trans-stilbenes and oxygen molecules in a zeolite NaY matrix at 313 nm leads to generation of the corresponding benzaldehydes in an electron-transfer process from which stilbene cation radicals and superoxide anion radicals arise. By contrast, excitation at 254 nm induces isomerisation and phenanthrene production, but without formation of any oxygenation products. 

The spectra show a displacement of the chlorpromazine peak at 3080-3100 A. While this slight bathochromic shift could be interpreted as evidence for the formation of a contact charge transfer complex, by itself it is not thought to be sufficient evidence. If heparin as an electron acceptor is forming a charge transfer complex with the strong electron donor chlorpromazine, a conductivity maximum should result. The opposite occurs. The role of hydrophobic bonding in the association should be considered. 

Many solvents form, on contact with oxygen, charge-transfer (CT) complexes. Aromatic hydrocarbons, e.g. benzene [440, 632, 633, 1111, 2139], toluene [2223], and even alkanes, e.g. cyclohexane [1111, 1525], interact with oxygen and form CT complexes. These compounds, in the presence of oxygen, exhibit electronic absorption bands which are not characteristic of either the hydrocarbon or oxygen. The stabilization energy of these complexes is extremely low and they have therefore been termed contact charge-transfer complexes [1111, 1635]. 

Solution of sulfur in very pure aliphatic tertiary amines produces only a moderate amount of heat and the solutions contain very few ions. However, the color of sulfur is a little more intense. The enhancement depends upon the base strength (trialkylamines>4-picoline> pyridine) of the amine. Steric requirements can reverse the basicity order (pyridine>2,6-lutidine). The most consistent explanation involves a contact charge-transfer complex which denotes the electrons on the nitrogen only as the light wave passes... 

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