1.3.5- Trinitrobenzene, charge-transfer complexes

The composition and nature of the charge-transfer complexes of 2-quinoxalina-mine with tetrachlorobenzoquinone (chloranil), tetrabromobenzoquinone (bromanil), 1,3,5-trinitrobenzen, and picric acid have been determined likewise those of 2,3-quinoxalinediamine with chloranil and bromanil. 

The formation of unusually light colored charge-transfer complexes of 8 with both picric acid and trinitrobenzene may be attributed to the decrease of the interaction between the donor and acceptor molecules due to the curvature of the former. ... 

The 7i-donor behavior of 4-arylmethylene-2-phenyl-5(47/)-oxazolones 762 with the 7i-acceptor tetracyanoethylene has also been studied. The initially formed charge-transfer complex is converted via intermediate 763 to a new compound for which a 2-aryl-l-benzamido-3,3,4,4-tetracyanocyclobutanecarboxylic acid 764 has been proposed on the basis of the NMR spectral data (Scheme 7.233). Charge-transfer complexes of 2-aryl-4-arylidene-5(47/)-oxazolones with di- and trinitrobenzene as n acceptors have also been prepared. ... 

Chemical evidence for the aromatic character of (232) is provided by its stability to acid and base. No tautomerization to imine forms such as (223) is detectable by NMR, indicating a lower limit of perhaps 84 kJ mol-1 for the stabilization energy. Finally, the 1,4-dimethyl derivative (230d) forms a charge transfer complex with trinitrobenzene (Amax 488). 

The usefulness of relaxation measurements as a probe for charge-transfer complexation was investigated for the pair trinitrobenzene and methylindole (Blackburn and Friesen, 1977). On addition of trinitrobenzene to a methylindole solution the 13C 7) values of methylindole decrease, an... 

Figure 8.71 Skeletal representations of face-to-face stacking in the X-ray crystal structures of some typical charge transfer complex co-crystals (a) naphthalene-TCNE, (b) skatole-trinitrobenzene, (c) perylene-fluoroanil (d) anthracene-trinitrobenzene and (e) TCNQ-TMPD.

Thompson C.C., Maine P.A.D. Solvent effects on charge-transfer complexes. II. Complexes of 1,3,5-trinitrobenzene with benzene, mesitylene, durene, pentamethylbenzene, or hexamethylbenzene // J. Phys. Chem. - 1965. - Vol. 69. - P. 2766-2771. 

Phenoxatellurin forms 1 1 charge-transfer complexes with 1,3,5-trinitrobenzene, picric acid, and picryl chloride4-6. 

Compound 142 (R = Me) formed a stable charge transfer complex with 1,3,5-trinitrobenzene (79AG(E)964). 

Several arene chromium tricarbonyl complexes form 1 1 adducts with Lewis acids such as tetracyanoethylene and 1,3,5-trinitrobenzene (TNB) 162, 227, 229, 259). The TNB adducts have been isolated as crystaline solids and the structure of the anisole derivative determined by X-ray analysis (57, 229). The plane of the TNB ring was found to be parallel to the anisole ring with an average separation of 3.41 A. This is a somewhat larger separation than that observed in the charge transfer complexes of TNB with aromatic molecules, and the increased separation was attributed to the strong electron-withdrawing capacity of the tricarbonyl chromium moiety which decreases the w-electron donor capacity of the anisole molecule 229). 

The electron affinity of trinitrobenzene which characterizes the ability of the compound to form charge-transfer complexes is not very high and is estimated to be equal to 0.6 eV, whereas stronger electron acceptors such as tetracyan-elhylene and chloranil show values of 1.6 and 1.35 eV respectively [86]. 

Spontaneous Crosslinking. In the absence of TCPA, evaporated solutions of XVIII can be completely redissolved in fresh solvent in a few minutes. And solutions of 0.05 M XVIII containing 0.007 M TCPA in acetonitrile are stable indefinitely (at least three weeks) at room temperature. However, on evaporation of the solvent under vacuum, the mixture forms a very tough film that is insoluble in acetonitrile or hot DMF, does not melt up to 300°, and is resistant to attack by chromic acid. The IR spectrum is identical to that of XVIII crossiinked BF3 or by irradiation in the presence of TCPA. Apparently as the solution becomes highly concentrated, crosslinking occurs by thermal excitation of charge-transfer complexes of TCPA and XVIII. The IR evidence and the insolubility behavior appear to discount an alternative possibility of simple association of polymer chains facilitated by the presence of the acceptor compound. The spontaneous crossiinking is also observed with the acceptors chloranil and 1,3,5-trinitrobenzene, and presumably would occur with others. 

One could, of course, look upon this as a charge transfer complex. A somewhat remote analogy is the reaction in benzene solution between dibenzene chromium(O) and electron acceptors like trinitrobenzene and chloranil 56a), which can be represented thus... 

Figure 4.14 Energy for the maximum absorbance for charge transfer complexes of s-trinitrobenzene, tetracyanoethylene, and chloranil with various donors plotted against the adiabatic ionization potential of the donor. Recent ionization potentials from the NIST tables were used. The vertical displacement results from the differences in the Ea of the molecules. The calculated curves were obtained by using a two-parameter nonlinear least squares. The values of the constants are given in Table 4.5, where they are compared with published values. Data from [8, 30, 32].

Figure 4.15 Electron affinities of charge transfer complex acceptors calculated from C2 = 2.9 versus the current best adiabatic electron affinities. This is a precision and accuracy plot. The zero intercept slope indicates that the same quantities are measured. The compounds are maleic anhydride, tetrachlorophthalic anhydride, benzoquinone, trinitro-flourenone, s-trinitrobenzene, chloranil, tetracyanoquinodimethane, and tetracyanoethylene in order of their electron affinities.

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