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Hexamethylbenzene, complex formation

The ability of compounds with double bonds to act both as electron donors and as electron acceptors in charge transfer complex formation is well known (81,82). Hammond (83) has studied the correlations of association constants and of the energy of the charge transfer absorption of 2-substituted-l,4-benzoquinones complexed with hexamethylbenzene with the Hammett equation. Charton (84) has studied the correlation with eq. (2) of association constants of 1-substituted propenes with Ag. ... [Pg.108]

The same conclusion is not applicable to the NO+ complexes, in which the magnitudes of the formation constants are much more strongly dependent on the ionization potential of the arene donor (see Fig. 10A). Thus the factor of >104 that separates the formation constant of the benzene complex with NO+ from that of the hexamethylbenzene complex corresponds to more than 5 kcal mol-1 of extra stabilization energy in the... [Pg.226]

On the other hand, the rate of complex formation in the solid state seems to depend greatly on steric circumstances. It is particularly low for those methylbenzenes, such as mesitylene or durene, which contain only isolated unsubstituted hydrogen atoms, or which are completely methylated (hexamethylbenzene). On complex formation the bands of the Lewis acid change in the same way as observed for benzene (Perkampus and Baumgarten, 1963). [Pg.218]

Dorr and Buttgereit (1963), using U.V. measurements of solutions of mesitylene and hexamethylbenzene in chloroform, bromoform, carbon tetrachloride and carbon tetrabromide, were able to demonstrate a weak electron transfer complex formation with these solvents. These investigations show that hexamethylbenzene is a more powerful electron donor than mesitylene. A similar influence on an acceptor property... [Pg.261]

Complex formation results in a downfield change in the chemical shift of the methyl protons and a decrease in the double-bond infrared stretching frequency from 1680 to 1532 cm h In the presence of a small excess of PdCl2, the complex is rapidly converted to hexamethylbenzene and palladium chloride. [Pg.314]

J0 The reaction of [Fe(t) -arene)] and Tl2[ V/o-7,8-C2B9Hii] results in arene displacement and formation of [l-(ij -arene)-c/oso-l,2,3-FeC2B9Hii] where the number of methyl substituents on the arene vary from 1 to 6 (B. Stfbr, M. Bakardjiev, J. Holub, A. Ruzicka, Z. Padelkovd, P. Stepnicka, Inorg. Chem., 2011, 50, 3097). Explain why product yields were lowest for the pentamethylbenzene and hexamethylbenzene complexes. Provide four unique trends (spectroscopic and electrochemical) that were correlated to increasing methyl substitution at the arene. [Pg.617]

Fig. 16. Polarographic data for complex formation as a function of donor concentration (in CHaCls at 25°). Hexamethylbenzene complexes of A, tetracyanoethylene B, tetra-cyanobenzene. Pyrene complexes of C, chloranil D, tetracyanobenzene E, tetracyano-quinondimethide. (Data from ref. 64)... Fig. 16. Polarographic data for complex formation as a function of donor concentration (in CHaCls at 25°). Hexamethylbenzene complexes of A, tetracyanoethylene B, tetra-cyanobenzene. Pyrene complexes of C, chloranil D, tetracyanobenzene E, tetracyano-quinondimethide. (Data from ref. 64)...
Thermodynamic data have been published for hexafluorobenzene and a number of its derivatives," for mixtures of hexafluorobenzrate with amines," and for the tetraftuoro-/ -beozoquinone-hexamethylbenzene complex. " The mixing properties of aromatic fluorocarbons have been discussed in some detail," and the formation of stable crystalline 1 1 molecular complexes of pafluorotriphenylene with triphenylene and of tetrafiuorophthalonitrile with aiylamines or polynuclear aromatic hydrocarbons has been noted. [Pg.218]

Indeed, the extent of disproportionation of NO according to equation (89) clearly depends on the donor strength of the aromatic hydrocarbon.240 For example, hexamethylbenzene which is a strong donor (IP = 7.85 V) promotes the ionization of NO to an extent of 80% whereas the weaker donor durene (IP = 8.05 V) affords less than 25% ion-pair formation. Furthermore, the resulting NO+ cation is a powerful electron acceptor (Erea = 1.48 V versus SCE) in contrast to NO (Ered = 0.25 V versus SCE) and thus readily forms donor/acceptor complexes with a variety of aromatic, olefinic and heteroatom-centered donors. Accordingly, the donor/acceptor complexation and electron-transfer activation are the critical steps in various transformations in Chart 8 as described below. [Pg.293]

The Kus can be estimated as follows an extrapolation of the Kus for the CT complex formed by any one donog such as mesitylene or hexamethylbenzene, with 1,3,5-trinitrobenzene and 1,4-dinitrobenzene to PhN02, and an extrapolation from solvent CC14 to one of DC > ca. 10 (Foster, 1969) shows that for our system Kus is very unlikely to be greater than 0.01 hmol"1. Therefore, with m = 1 mold"1, and [Sv] = 10 mold"1, [MSv] < 0.1 mold 1. This means that for styrene and other 7t-donors effectively all the monomer is free. For n-donor monomers such as the VE, however, the fraction of uncomplexed monomer may be somewhat smaller. Therefore it appears that the formation of CT complexes probably did not affect significantly at least the results for the three hydrocarbon monomers. [Pg.556]

Dimercury(I) n complexes are formed between aromatic compounds and Hg2(AsF6)2 in liquid S02 as solvent.113,121 Insoluble complexes with the ratio arene Hg2+ = 1 1 (arene = benzene, naphthalene, 2-methylnaphthalene, 2,6-dimethylnaphthalene, acenaphthene, fluor-anthrene, phenanthrene, anthracene, 9,10-dimethylanthracene or 1,3-dinitrobenzene) or 1 2 (arene = 9,10-benzophenanthrene) have been characterized by elemental analysis and, in some cases, by Raman spectrometry.113,120 The 13CNMR data allow the estimation of formation constants for the hexamethylbenzene, p-xylene and 1,4-dichlorobenzene complexes together with the chemical shifts for the bound substrates in these cases.121 Probably the coordination compounds of dimercury(I) salts with carbazole, dibenzofuran and diben-zothiophene are also n complexes.122... [Pg.1058]

Nitronium tetrafluoroborate used in large excess (>6 equiv.) is able to transform hexamethylbenzene and its derivatives to dinitroprehnitene (1,2,3,4-tetramethyl-5,6-dinitrobenzene) in a highly selective nitration process486 [Eq. (5.180)]. Scheme 5.47 summarizes the key steps of the mechanistic proposal, including the ipso - n i tro are n iu m ion 123, the formation of benzyl nitrite 124, and the complexation of the N02+ ion to form the mononitro intermediate (125) facilitating the attack to the ortho position resulting in the formation of the 1,2-dinitro product. [Pg.639]

Bryce-Smith and Gilbert have shown that toluene, t-butylbenzene, chlorobenzene, o- andp-xylene, and biphenyl all undergo photoaddition to maleic anhydride, yielding 1 2 adducts [33], All the substituents decrease the rate of formation of adducts. Benzonitrile, nitrobenzene, phenol, methyl benzoate, durene, hexamethylbenzene, naphthalene, and biphenylene fail to undergo the addition of these, benzonitrile, nitrobenzene, methyl benzoate, and biphenylene do not form charge-transfer complexes. Bradshaw [34] found that various alkylben-zenes give 1 2 adducts with maleic anhydride upon photosensitization with acetophenone. [Pg.6]

Charge transfer (CT) complexes are kept together by rather weak forces, and it is not to be expected that such forces should influence their electrochemical behaviour significantly. Thus, the CT complex between tetracyanoethylene and hexamethylbenzene has its halfwave potential for reduction shifted 0-039 V towards a more negative potential as compared to tetracyanoethylene itself (Peover, 1967) as is predictable from theoretical considerations of the formation of the CT complexes. [Pg.47]

In contrast, electron transfers from unhindered (or partially hindered) donors such as hexamethylbenzene, mesitylene, di-ferr-butyltoluene, etc. to photoactivated quinones exhibit temperature-independent rate constants that are up to 100 times faster than predicted by Marcus theory, poorly correlated with the accompanying free-energy changes (see Figure 20A), and only weakly affected by solvent polarity and salt effects. Most importantly, there is unambiguous (NIR) spectroscopic and kinetic evidence for the pre-equilibrium formation K c) of long-lived encounter complexes (exciplexes) between arene donor (ArH) and photoexcited quinone acceptor (Q ) prior to electron transfer (A et) [20] (Eq. 95). [Pg.1331]

Trialkyl and triaryl Cr(III) compounds are effective in promoting the cyclic trimerization of disubstituted acetylenes to aromatic hydrocarbons 222, 457). In the reaction of Ph3Cr -3THF with 2-butyne, the bisarene complexes of hexamethylbenzene and 1,2,3,4-tetramethylnaphthalene are obtained, as well as the free aromatic hydrocarbons 222). It is clear that a phenyl substituent has been incorporated in the formation of the coordinated and uncoordinated 1,2,3,4-tetramethylnaphthalene. Al-... [Pg.62]

It is well known that palladium chloride is an active catalyst for the cyclization of acetylene to form cyclobutadiene as well as benzene derivatives. In this reaction an intermediate complex was isolated which has a palladium carbon a-bond, the formation of which was explained by an insertion mechanism, not by concerted cyclotrimerization. When this complex obtained from butyne and palladium chloride was decomposed by various means, 5-vinyl-l,2,3,4,5-penta-methylcyclopentadiene and 5-(l-chlorovinyl)-l,2,3,4,5-pentamethylcyclopenta-diene were obtained in addition to hexamethylbenzene... [Pg.76]

When the charge-transfer complex between hexamethylbenzene (123) and oxygen is irradiated (313nm) in methanol, a methoxymethyl derivative and pentamethylanisole are formed. These are not the products obtained when singlet oxygen attacks (123) see structure (62). Finally in this section, an example of substitution in benzene by a phosphorus-centred radical is seen in the formation of O-ethyl diphenylphosphinate (124) as one of the products of photolysis of O-ethyl 5-propyl phenylphosphonotli o e in benzene. ... [Pg.368]


See other pages where Hexamethylbenzene, complex formation is mentioned: [Pg.178]    [Pg.237]    [Pg.45]    [Pg.446]    [Pg.399]    [Pg.424]    [Pg.419]    [Pg.421]    [Pg.814]    [Pg.287]    [Pg.226]    [Pg.457]    [Pg.462]    [Pg.465]    [Pg.108]    [Pg.4112]    [Pg.1405]    [Pg.1448]    [Pg.1036]    [Pg.65]    [Pg.92]    [Pg.117]    [Pg.978]    [Pg.226]    [Pg.220]    [Pg.340]    [Pg.184]    [Pg.256]   
See also in sourсe #XX -- [ Pg.85 , Pg.89 ]




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Hexamethylbenzene, complex

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