Amines, charge transfer

Although iodine has been most extensively studied, chlorine and bromine show similar behavior. For a given group of donors, the frequency of the intense charge-transfer absorption band in the ultraviolet is dependent upon the ionization potential of the donor solvent molecule, and electronic charge can be transferred either from a -electron system as in benzene or from lone-pairs as in ethers or amines. Charge-transfer spectra and complexes are of importance elsewhere in chemistry. 

Fullerene-amine charge transfer complex formation has also been studied at different temperamres to determine thermodynamic parameters of the equilibria. For Cg4-DEA as an example, observed absorbances decrease systematically with increasing temperature, which is due to a shift in the complex formation equilibrium with temperature, because molar absorptivities of in toluene are essentially temperature independent [92]. 

Burdeniuc. J. Sanford, M. Crabtree. R.H. Amine charge transfer complexes of perfluoroalkanes and an application... 

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. 

Charge-Transfer Compounds. Similat to iodine and chlorine, bromine can form charge-transfer complexes with organic molecules that can serve as Lewis bases. The frequency of the iatense uv charge-transfer adsorption band is dependent on the ionization potential of the donor solvent molecule. Electronic charge can be transferred from a TT-electron system as ia the case of aromatic compounds or from lone-pairs of electrons as ia ethers and amines. 

Reaction Mechanism of Vinyl Polymerization with Amine in Redox and Photo-Induced Charge-Transfer Initiation Systems... 

A substantial number of photo-induced charge transfer polymerizations have been known to proceed through N-vinylcarbazole (VCZ) as an electron-donor monomer, but much less attention was paid to the polymerization of acrylic monomer as an electron receptor in the presence of amine as donor. The photo-induced charge-transfer polymerization of electron-attracting monomers, such as methyl acrylate(MA) and acrylonitrile (AN), have been recently studied [4]. In this paper, some results of our research on the reaction mechanism of vinyl polymerization with amine in redox and photo-induced charge transfer initiation systems are reviewed. 

The diacyl peroxide-amine system, especially BPO-DMT or BPO-DMA, has been used and studied for a long time but still no sound initiation mechanism was proposed. Some controversy existed in the first step, i.e., whether there is formation of a charge-transfer complex of a rate-controlling step of nucleophilic displacement as Walling 1] suggested ... 

The well-known photopolymerization of acrylic monomers usually involves a charge transfer system with carbonyl compound as an acceptor and aliphatic tertiary amine, triethylamine (TEA), as a donor. Instead of tertiary amine such as TEA or DMT, Li et al. [89] investigated the photopolymerization of AN in the presence of benzophenone (BP) and aniline (A) or N-methylaniline (NMA) and found that the BP-A or BP-NMA system will give a higher rate of polymerization than that of the well-known system BP-TEA. Still, we know that secondary aromatic amine would be deprotonated of the H-atom mostly on the N-atom so we proposed the mechanism as follows ... 

The reaction between the photoexcited carbonyl compound and an amine occurs with substantially greater facility than that with most other hydrogen donors. The rate constants for triplet quenching by amines show little dependence on the amine a-C-H bond strength. However, the ability of the amine to release an electron is important.- - This is in keeping with a mechanism of radical generation which involves initial electron (or charge) transfer from the amine to the photoexcited carbonyl compound. Loss of a proton from the resultant complex (exciplex) results in an a-aminoalkyl radical which initiates polymerization. The... 

Charge-transfer complexes with pyrimidine and purine bases as well as with solvents like hexa-methylphosphoramide and dimethyl sulfoxide are reported in Ref 66. The action of aromatic amines (primary, secondary, or tertiary) resulted in fume-offs or unidentifiable tars, in all cases purple or red colors developed prior to more violent reactions (Ref 66)... 

In 159 and 163-166 the tertiary amine function is coordinated to the boron atom and transmits the electronic change due to the ester formation to the chromophore. In 160-162 the boron atom is directly connected to the chromophore. After the complexation of the saccharide, the change of the charge transfer, e.g., for 159 [249-251], or the fluorescence bands, e.g., for 160-166 [252-255], can be measured and interpreted. The most selective binding of n-glucose has been achieved with host 164 that forms a 1 1 complex with a macrocyclic structure (Scheme 1). 

The donor-acceptor formation can be considered by transfer of electrons from the donor to the acceptor. In principle one can assume donor-acceptor interaction from A (donor) to B (acceptor) or alternatively, since B (A) has also occupied (unoccupied) orbitals, the opposite charge transfer, from B to A. Such a view refers to mutual electron transfer and has been commonly estabUshed for the analysis of charge transfer spectra of n-complexes [12]. A classical example for a donor-acceptor complex, 2, involving a cationic phosphorus species has been reported by Parry et al. [13]. It is considered that the triaminophosphines act as donor as well as an acceptor towards the phosphenium cation. While 2 refers to a P-donor, M-donors are in general more common, as for example amines, 3a, pyridines, 3b, or the very nucleophilic dimethylaminopyridine (DMAP) [ 14], 3c. It is even a strong donor towards phosphorus trichloride [15]. 

In recent publications, Gugumus (6) and Felder et al (13,14) have proposed a modification of the Boozer-Hammond mechanism (15) to explain their observed kinetics in the inhibition of ketone photo-oxidations by hindered amine species (reaction 10). Peroxyl radicals were suggested to form charge transfer complexes with the... 

Herbich J, Kapturkiewicz A (1991) Radiative and radiationless depopulation of the excited intramolecular charge transfer states aryl derivatives of aromatic amines. Chem Phys 158 143-153... 

Blackstock, S. C., J. P. Lorand, and J. K. Kochi. 1987. Charge Transfer Interactions of Amines with Tetrahalomethanes. X-ray Crystal Structures of the Donor-Acceptor Complexes of Quinuclidine and Diazabicyclo-[2.2.2]octane with Carbon Tetrabromide. J. Qrg. Chem. 52,1451. 

Amines possess a pair of p-electrons on the nitrogen atom. The nitrogen atom has a low electron affinity in comparison with oxygen. Therefore, amine can be the electron donor reactant in a charge-transfer complex (CTC) in association with oxygen-containing molecules and radicals. It will be shown that the formation of CTC complexes of amines with peroxyl radicals is important in the low-temperature oxidation of amines. 

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