Donor-acceptor type

In this mechanism, a complexation of the electrophile with the 7t-electron system of the aromatic ring is the first step. This species, called the 7t-complex, m or ms not be involved directly in the substitution mechanism. 7t-Complex formation is, in general, rapidly reversible, and in many cases the equilibrium constant is small. The 7t-complex is a donor-acceptor type complex, with the n electrons of the aromatic ring donating electron density to the electrophile. No position selectivity is associated with the 7t-complex. 

From elemental sulfur to selenium and tellurium, intermolecular interactions (,secondary bonds, soft-soft interactions) play an increasing role. According to N. W. Alcock,1 the term secondary bond describes interatomic distances longer than covalent single bonds but shorter than van der Waals interatomic distances.1 In many cases secondary bonds can also be described as coordinative Lewis base - Lewis acid or charge transfer (donor-acceptor) types of interactions. 

Among the M(dmit)2-based superconductors, a-(EDT-TTF)[Ni(dmit)2] is also of donor-acceptor type and has two outstanding features it is the only one to contain a 1 1 molar ratio of donor and acceptor units and to exhibit superconductivity at ambient pressure [32]. It was found to be superconductive below 1.3 K under ambient pressure (Fig. 3). 

Once again the active species is an associative D-A complex =CH2-SR2 of donor-acceptor type, but - in contrast to the positive modifiers - the negative modifiers are the donors, and the acceptor (the acidic CH2) is part of the polymer end-group. 

Most of the devices described up to now are based on materials that tend to crystallize [phthalocyanines, porphyrins and perylenetetracarboxydiimids, (59)] [276, 277], or form liquid crystalline phases [278, 279]. With respect to amorphous glasses, light sensitive donor-acceptor type molecules, for example, the p-type triarylamines tris [4-methylphenyl(4-nitrophenyl)ammo]triphenylamine and tris[5-(dimesitylboryl)thiophen-2-yl]triphenylamine have been combined with an n-type material in a double-layer heterostructure [280]. The cells respond to visible light from 400 to 800 nm with overall efficiencies of 0.1%. 

The same dichotomy of bonding models is also found for carbyne complexes that have a formal triple bond M=CR. There are metal-carbyne bonds that belong to the donor-acceptor type (the Fischer car-... 

The change of the spectral characteristics, as well as the fact of the dissolution of fullerene C in water with PVP itself, confirms the formation of interaction between the fullerene and PVP, most probably of a donor-acceptor type. According to the NMR 13C data in D20 the electronic state of carbon atoms C(1) and C(4) of pyrrolidone cycle and C(5) of monomer unit of PVP, nearest to nitrogen atom, cardinally changes in the complex (Vinogradova et al., 1998). 

U, 3A, 5A -Triphosphinines were also investigated. In the homodesmotic reaction in eq 10 (X = PH2), 21.8 kcal/mol stabilization has been obtained at the MP2/ 6-31G(d) level (cf. with the 26.0 kcal/mol value for 12. 32. 5A -triphosphinine at the same level of the theory). This stabilization is in agreement with the cyclic delocalization stabilization resulting from donor—acceptor-type interactions discussed in section... 

Excited molecular complexes of the donor-acceptor type are called excimers if formed from identical molecules and exiplexes if originated from different molecules. From the theory, it is concluded that photochemical influence will more readily accelerate electron transfer in a weak donor-acceptor pair than in a strong pair (Juillard and Chanon 1983). An organic molecule in an electron-excited state is a more active oxidant or stronger reducer than the same molecule in a ground state. 

The blue phosphor of long standing is ZnS Ag, which has a radiant efficiency close to the theoretical limit. It is a donor-acceptor type phosphor, with silver ions acting as the acceptor in the ZnS with either aluminium or chlorine as the donors on zinc or sulfate sites. 

Liu Z, He D, Wang Y et al (2010) Solution-processable functionalized graphene in donor/ acceptor-type organic photovoltaic cells. Solar Energy Mater Solar Cells 94 1196-1200... 

Contrary to anomalously distant reacting double bonds, the mixed crystal of 1 1 donor-acceptor type cinnamic acids has been reported to be photostable, in which double bonds of adjacent donor and acceptor components in the stack are within photoreactive distance of each other (3.80 A) (14). 

It is assumed that this behaviour can be explained by an additional interaction between the undivided p-electrons of the oxygen atom and the vacant 3d-orbitals of the silicon atom (the so called (p -dj-interaction).96 The ideas about the nature of the siloxane bond were developed by Voronkov.97 He stated that (pT-dT)-bonds of a donor-acceptor type are formed in a Si-O-Si system owing to the undivided electron pairs of oxygen and the vacant d-orbitals of the silicon atoms. In this case, the oxygen atom is in a state of hybridization, intermediate between sp2 and sp. 

This requirement could best be satisfied by formation of a complex— perhaps of the donor-acceptor type—or an actual compound, a phenyl-cyclohexadiene (13), between two molecules of benzene or other aromatic compound, in which protium and deuterium atoms readily move and exchange. 

In summary, it is noted that multiple bonding between the heavier Group 14 elements E (Ge, Sn, Pb) differs in nature in comparison with the conventional a and 7T covalent bonds in alkenes and alkynes. In an E=Ebond, both components are of the donor-acceptor type, and a formal E=E bond involves two donor-acceptor components plus a p-p n bond. There is also the complication that the bond order may be lowered when each E atom bears an unpaired electron or a lone pair. The simple bonding models provide a reasonable rationale for the marked difference in molecular geometries, as well as the gradation of bond properties in formally single, double and triple bonds, in compounds of carbon versus those of its heavier congeners. 

In the discussion of the spatial structure of organic compounds of the heavy silicon subgroup elements it is necessary to dwell on their molecular structure, structure of condensed state and complexes of donor-acceptor type. 

Abstract. A comparative investigation of C6o fiillerene solubility and donor force of alkyl derivatives of benzene has been performed. Based on the found correlation, which was determined by current methods, between C6o solubility and donor force of solvents, it has been concluded that the process of Cgo dissolution in aromatic hydrocarbons is a process of intermolecular interaction combined with charge-transfer and formation of complexes of the donor-acceptor type. The agreement between a series of physical and chemical phenomena (factors, properties) observed in studies of C60 solubility and a number of existing criteria which allow the phenomena to be interpreted as a manifestation of the charge-transfer interaction substantiates our conclusion. 

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