Electron donor-acceptor compounds

In this chapter, we will discuss the recent results regarding the development of molecular switches and logic gates toward information processing at the molecular level based on electroactive molecules and supramolecules. Also, we will illustrate the progress of application of electron donor-acceptor compounds in high-density information storage. 

The UV spectra suggest that the equilibrium between the diazonium ion and the solvent, on the one hand, and an electron donor-acceptor complex (8.58) on the other, lies on the side of the complex. The latter may possibly exist also as a radical pair (8.60) or a covalent compound (8.59). Dissociation of this complex within a cage to form an aryl radical, a nitrogen molecule, and the radical cation of DMSO is slow and rate-determining. Fast subsequent steps lead to the products observed. 

When the reaction of two compounds results in a product that contains all the mass of the two compounds, the product is called an addition compound. There are several kinds. In the rest of this chapter, we will discuss addition compounds in which the molecules of the starting materials remain more or less intact and weak bonds hold two or more molecules together. We can divide them into four broad classes electron donor-acceptor complexes, complexes formed by crown ethers and similar compounds, inclusion compounds, and catenanes. 

Helms A, Heiler D, McLendon G (1992) Electron transfer in bis-porphyrin donor-acceptor compounds with polyphenylene spacers shows a weak distance dependence. J Am Chem Soc 114 6227-6238... 

Structurally related to these species are the triply branched compound 56+ and its rotaxanes 66+, 76+, and 86+ (Fig. 13.6)9, in which one, two, or three acceptor units are encircled by the electron donor macrocyclic compound 2. Although these rotaxanes cannot behave as degenerate molecular shuttles because of their branched topology, they are nevertheless interesting from the electrochemical viewpoint. 

A common way to determine Kid values is to measure sorption isotherms in batch experiments. To this end, the equilibrium concentrations of a given compound in the solid phase (Cis) and in the aqueous phase (CIW) are determined at various compound concentrations and/or solid-water ratios. Consider now the sorption of 1,4-dinitrobenzene (1,4-DNB) to the homoionic clay mineral, K+-illite, at pH 7.0 and 20°C. 1,4-DNB forms electron donor-acceptor (EDA) complexes with clay minerals (see Chapter 11). In a series of batch experiments, Haderlein et al. (1996) measured the data at 20°C given in the margin. 

Table 11.2 Adsorption of Nonionic Nitroaromatic Compounds (NACs) to Aluminosilicate Clays (a) Surface Area Factors,/saf, for Different Clays Expressing Maximum Sorption Sites Relative to Kaolinite, and (b) KNAC EDA Values (L- mol 1 sites) Measured for Several NACs on K+-Kaolinite Allowing Estimates of KNACd Values Due to Electron Donor-Acceptor Interactions (Eq. 11-20) ...

Aromatic compounds have a special place in ground-state chemistry because of their enhanced thermodynamic stability, which is associated with the presence of a closed she of (4n + 2) pi-electrons. The thermal chemistry of benzene and related compounds is dominated by substitution reactions, especially electrophilic substitutions, in which the aromatic system is preserved in the overall process. In the photochemistry of aromatic compounds such thermodynamic factors are of secondary importance the electronically excited state is sufficiently energetic, and sufficiently different in electron distribution and electron donor-acceptor properties, ior pathways to be accessible that lead to products which are not characteristic of ground-state processes. Often these products are thermodynamically unstable (though kinetically stable) with respect to the substrates from which they are formed, or they represent an orientational preference different from the one that predominates thermally. 

A second major mode of photocydoaddition involves 1.2-addition to the aromatic ring, and this predominates if there is a large difference in electron-donor/acceptor capacity between the aromatic compound and the alkene. It is therefore the major reaction pathway when benzene reacts with an electron-rich alkene such as 1,1-dimethoxyethylene (3.43) or with an electron-deficient alkene such as acrylonitrile (3.441. When substituted benzenes are involved, such as anisole with acrylonitrile (3.45), or benzonitrile with vinyl acetate (3.46), reaction can be quite efficient and regioselective to give products in which the two substituents are on adjacent carbon atoms. 

The use of electron donor—acceptor complexes has been reported for the visualization and MS identification of compounds separated by TLC [193,194]. The mass spectra of the donor and of the acceptor can be separated by using different probe temperatures. 

Ambiphilic derivatives, also called amphoteric derivatives, are polyfunctional compounds combining Lewis bases and Lewis acids (Figure 1). Such donor-acceptor compounds typically combine group 15 and 13 elements featuring, respectively, a lone pair of electrons and a vacant orbital. Among the possible combinations, phosphine-boranes (PB) clearly occupy a forefront position. 

Photoinduced electron-transfer reaction of aromatic compounds with amines is one of the most fundamental reactions in the electron-donor-acceptor systems, which was recently reviewed by Lewis [35], Because of the low oxidation potentials of the amines, the photoinduced one-electron transfer from the amines to the excited singlet states of aromatic hydrocarbons ( Aril ) readily occurs to give the radical cations of amines and the radical anions of aromatic compounds even in the less polar solvents. 

Reactivity of Electron Donor-Acceptor Complexes. Part. 6. Hydrogen Exchange of Aromatic Cyano-Substituted Compounds. Trans. Faraday Soc. 63, 997 (1967). 

Hydrogen Exchange Reaction between Molecular Hydrogen and the Electron Donor-Acceptor Complexes of Various Aromatic Compounds. Bull. Chem. Soc. Japan 40, 1015(1967). 

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