Amine, aromatic, charge-transfer

Fluorescence quenching of fluorene, dibenzofuran, and dibenzothiophens by aromatic nitriles and aliphatic amines is the result of electron transfer with exciplex formation,177 and ion-pair formation in pyromellitic dianhydride-ethylbenzene is followed by dissociation into separated ion pairs in their highly excited states.178 Photochemical iodination of aromatic hydrocarbons may proceed by way of an electronically excited Ia-aromatic charge-transfer complex.179 Modulation excitation spectrophotometry has been used to analyse the nature of some complexes between polycyclic aromatic hydrocarbons and chloranil.180... 

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. 

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 ... 

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)... 

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... 

The SET between amine and acceptor may be enhanced by photoexcitation and may lead to the formation of exciplexes2 or molecular complex with charge transfer character3. The photochemistry between aromatic acceptors and amines via the exciplexes has been discussed earlier (Scheme l)4. 

We have mentioned above the prevalence of chromoisomeric effects in two-component systems forming solid charge-transfer complexes. This was studied first by Hertel (120) and labeled by him complex isomerism. In a system such as picric acid with an aromatic amine, there are a variety of structural possibilities. There will probably be intermolecular hydrogen bonds, which are associated with short lateral contacts between the near-planar molecules. In addition, there... 

In fac-(bpy)Re(I) (CO)3-A (where bpy is 2,2 -bipyridine and A is an aromatic amine), the d-7t(Re)—>jr (bpy) MLCT fluorescent excited state is strongly quenched via intramolecular aniline-Re charge transfer leading to a nonfluorescent LLCT state. By incorporating the donor amino group belonging to the A moiety into a crown-macrocycle, Schanze and Mac Queen(137) have provided a new luminescent cation sensor whose quantum yield of fluorescence raises from 0.0017 (without cation) to... 

Another important mechanism, which is responsible for the formation of the colored products in the reaction between nitroaromatic compounds and some basic reagents such as aromatic amines, is the well-known charge transfer mechanism [16-19]. The aromatic amine acts as a 7l donor whereas the nitroaromatic compound serves as a 7l acceptor. 

Alkali, alkaline-earth, and rare-earth metal cations also catalyze electron transfer reactions. Thus, in the pair of Co -tetraphenylporphyrin complex with BQ, no redox reaction takes place, or it takes place too slowly to be determined. The metal cations promote this reaction. For example, in the presence of 80(0104)3, the corresponding rate constant of 2.7 X 10 M s was observed. BQ transforms into benzosemiquinone under these conditions (Fukuzumi and Ohkubo 2000). Zinc perchlorate accelerates the reaction between aromatic amines and quinones (Strizhakova et al. 1985). This reaction results in the formation of charge-transfer complexes [ArNHj Q ]. The complexes dissociate in polar solvents, giving ion-radicals ... 

Examples of such charge-transfer complexes include the complex formed between a metal ion and a -n orbital of a double bond or an aromatic system , the complex formed between polynitro aromatics (such as picric acid) and other w-orbital-containing molecules, and complexes of I2 and Br2 with amines, ketones, aromatics, etc ° Phenols and quinones also form charge-transfer complexes ... 

Monoamine oxidase catalyzes the deamination of primary amines and some secondary amines, with some notable exceptions. Aromatic amines with unsubstituted a-carbon atoms are preferred, but aromatic substituents influence the binding of these substrates. For example, m-iodobenzylamine is a good substrate, whereas the o-iodo analog is an inhibitor. The mechanism of deamination is as follows hydrolysis of the Schiff base that results from loss of a hydride ion on an a-proton yields an aldehyde, which is then normally oxidized to the carboxylic acid. Aromatic substrates are probably preferred because they can form a charge-transfer complex with the FAD at the active site, properly... 

Additions to Aromatic Hydrocarbons. A variety of photochemical additions to aromatic hydrocarbons have been reported. Benzene and its derivatives add to maleic anhydride74-76 as well as to simple olefins,77-80 isoprene,81 acetylene derivatives,79,82 and alcohols.83 The mechanism of the maleic anhydride-benzene reaction is discussed in Section IV. A.4. Naphthalene forms a photoadduct with dimethyl acetylenedicarboxylate62 and with acrylonitrile8211 while anthracene behaves similarly with maleic anhydride84 and with 1,2-benzanthracene.85 The photoaddition of several aromatic amines to anthracene has been reported to proceed via a charge transfer complex86,87 in fact, the majority of these addition reactions may proceed in this manner. 

TNT forms charge-transfer, or 7r, complexes with polycyclic aromatic hydrocarbons, aromatic amines, and aromatic nitro compds a number of these are listed below in Table 2. The complexes with three amines (diphenylamine, diethyl-aniline, p-anisidine) have characteristic colors this forms the basis for a rapid and convenient thin-layer chromatographic analytical procedure (Ref 34) for the identification of very small amounts of TNT. (For a discussion of the many color reactions of TNT, and of composite expls containing it, see Vol 3, C405-L ff)... 

Zinc perchlorate accelerates the reaction between aromatic amine and quinones (Strizhakova et al. 1985). The reaction results in the formation of charge-transfer com-... 

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 ... 

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