Amine, aromatic, charge-transfer interaction

NMR signals of the amino acid ligand that are induced by the ring current of the diamine ligand" ". From the temperature dependence of the stability constants of a number of ternary palladium complexes involving dipeptides and aromatic amines, the arene - arene interaction enthalpies and entropies have been determined" ". It turned out that the interaction is generally enthalpy-driven and counteracted by entropy. Yamauchi et al. hold a charge transfer interaction responsible for this effect. 

Interaction within encounter pairs. The above arguments have assumed that there is no interaction between the components in the encounter pairs A. B and B.X (Scheme 3) but this is probably unrealistic. Stabilization of the encounter pair A. B by charge-transfer interaction should favour the pre-association path by reducing the value of k 3 and possibly also increasing that of k4 [cf. equation (46)].22 Thus, in the nitration of neutral amine molecules (X) by nitronium ions (B) in concentrated sulphuric acid, interaction between the components in the encounter pair ArNHJ.NOJ should increase the acidity of the N—H hydrogens and facilitate the formation of the free amine. In the bromination of aromatic compounds (B) by HOBr(A), interaction between the components should increase the concentration of the encounter pair ArH. HOBr and facilitate the protonation of the hypobromous acid. 

Feng, Cao, and Li [9] studied the photopolymerization of acceptor monomers initiated by donor initiators, especially by aromatic amines. The proposed mechanism involved a charge-transfer interaction, followed by proton-transfer to produce two kinds of free radicals. The acrylonitrile (AN)/W,V-dimethyltoluidine (DMT) system is shown as an example ... 

Fullerene-Doped Polyvinylcarbazole. Fullerenes are known to be good electron acceptors. In the presence of electron donors such as aromatic amines, weakly bonded charge-transfer complexes can be formed [115]. Through virtual excitation, the existence of charge-transfer interaction can enhance the second-order optical nonlinearity of fullerenes [116], With direct excitation, excited state electron transfer between fullerenes and various electron donors such as aromatic amines [115,117], semiconductor colloids [118], porphyrin [119], and polymers [101, 103, 120] can occur. This electron-accepting property led to the development of fullerene-doped polymeric photoconductors [101,103]. 

These interactions are, however, more complex than has been indicated thus far. A solution of -trinitrobenzene in pyridine showed a marked increase in conductivity with time as did mixtures of -trinitrobenzene with diethylamine in ethanol (43). In the latter system a 1 1 complex is formed. Miller and Wjume-Jones (56) have discussed these results in terms of MuUiken s concept of inner and outer complexes (49) and have suggested that an outer complex forms, that this is in equilibrium with an inner complex, essentially an ion-pair, which in an ionizing solvent can dissociate into two solvated radical-ions. This is supported by the detection of a weak ESR absorption in solutions of s-trinitrobenzene in diethylamine both in the presence and absence of acetone (56). The rate of reaction between diethylamine and s-trinitrobenzene in acetone-ether (1 3 molar) has been studied by a stopped flow method (57). This rapid, reversible reaction is of first order in s-trinitrobenzene and second order in diethylamine and has been interpreted in terms of a rapid preliminary equilibrium, possibly the dimerization of the amine, and the formation of a charge-transfer complex. With aromatic amines the reactions involved proved too fast to measure. 

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