Toluene dimerization

The Benzene Dimer A Good Model for n-n Interactions in Proteins A Comparison Between the Benzene and the Toluene Dimers in the Gas Phase and in Aqueous Solution. 

Although the benzene dimer has been extensively studied as a prototype for the tt/tt interaction, its relevance to general properties of aromatic residues in proteins was questioned. The toluene dimer was instead proposed as a better prototype for the tt/tt interaction in proteins [65]. MP2 calculations show that the stacked dimers are substantially stabler than the T-shaped one [65,66] and that the antiparallel dimer is 0.9 kcal/mol stabler than the parallel dimer [66]. Recently reported CCSD(T) calculations of the toluene dimer show that the cross dimer (- 4.08 kcal/mol) is slightly stabler than the antiparallel and parallel dimers (- 3.77 and - 3.41 kcal/mol, respectively), as shown in Table 4 [10]. These stacked dimers are substantially stabler than the T-shape dimer (- 2.62 kcal/mol). Spectroscopic measurements show that the toluene dimer consists of at least two isomers [67,68). The interaction energy of the toluene dimer ( e) obtained from a CCSD(T) calculation (- 4.1 kcal/mol) is not very different from the experimental Eg value (- 3.6 kcal/mol) [69]. 

Dispersion is again the major source of the attraction in the toluene dimer [10]. The dispersion energies of the stacked toluene dimers are substantially larger than the dispersion energy of the slipped-parallel benzene dimer. The larger dispersion interaction in toluene is the cause of the preference for the stacked orientation, as in the case of the naph-... 

F. L. Gervasio, R. Chelll, P. Procacci, V. Schettino, "Is the T-shaped toluene dimer a stable intermolecular complex ", J. Phys. Chem. A, 2002,106,2945-2948. 

The S Si absorption spectrum was composed of the bands resembling the 1,2,4,5-tetracyanobenzene anion and toluene dimer cation. Similar results were observed also in the systems... 

Higher dimeric ketenes are flammable but have higher flash points and are less reactive than diketene. Almost no data are available. Diketene can be disposed of by incineration, preferably after dilution with an inert solvent such as toluene. Higher ketene dimers can also be incinerated. 

In certain cases, even dimers of certain isocyanates, such as toluene diisocyanate or hexamethylene diisocyanate, can act as blocking agents, thermally reversing to regenerate the isocyanate [16,17]. 

Reinhoudt, Gray, Smit and Veenstra prepared a number of monomer and dimer crowns based on a variety of substituted xylylene units. They first conducted the reaction of 1,2-dibromomethylbenzene and a polyethylene glycol with sodium hydride or potassium Z-butoxide in toluene solution. Mixtures of the 1 1 and 2 2 (monomer and dimer) products were isolated and some polymer was formed . The reaction was conducted at temperatures from 30—60° and appeared to be complete in a maximum of one hour. The authors noted that the highest yield of 1 1 cyclic product was obtained with disodium tetraethylene glycolate instead of dipotassium hexaethylene gly-colate (see also Chap. 2) . Chloromethylation of 1,3-benzodioxole followed by reaction with disodium tetraethylene glycolate afforded the macrocycle (29% yield) illustrated in Eq. (3.20). 

The corresponding tellurium diimide BuNTe( -N Bu)2TeN Bu (10.7) may be obtained in good yields from the reaction of lithium tert-butylamide with TeCU in THE (Eq. 10.3). °" In toluene solution this reaction also produces the cyclic tellurium(II) imide (TcN Bu)3. The dimer 10.7 is obtained as an orange solid, which can be purified by vacuum sublimation at ca. 90°C. 

Attempts to prepare the mono(cyclopenta-dienyl) derivatives are sometimes frustrated by a Schlenk-type equilibrium (see p. 132), but judicious choice of ligands, solvent etc. occasionally permits the isolation of such compounds, e.g. the centrosymmetric halogen-bridged dimer (t - -C5Me5)Ca(/i-l)(lhf)2 2] which cry.stallizes from toluene solution. The complex is isostruc-tural with the dimeric organosamarium(ll) analogue. - ... 

When methyl 2-(indol-2-yl)acrylate derivative (22a) reacted with A-methoxy-carbonyl-l,2-dihydropyridine (8a) in refluxing toluene, in addition to the dimer of 22a (25%), a mixture of the expected isoquinculidine 23a and the product 24a (two isomers) was obtained in 7% and 45% yields, respectively (81CC37). The formation of 24a indicates the involvement of the 3,4-double bond of dihydropyridine. Similarly, Diels-Alder reaction of methyl l-methyl-2-(indol-2-yl)acrylate (22b) with 8a gave, in addition to dimer of 22b, a mixture of adducts 23b and 24b. However, in this case, product 23b was obtained as a major product in a 3 2 mixture of two isomers (with a- and (3-COOMe). The major isomer shows an a-conhguration. The yields of the dimer, 23b, and 24b were 25%, 30%, and 6%, respectively. Thus, a substituent on the nitrogen atom or at the 3-position of indole favors the formation of the isoquinuclidine adduct 23. 

Comparison of the dimerization of 1-butene with [(H-COD)Ni(hfacac)] in chloroaluminate ionic liquids with the identical reaction in toluene is quite instructive. First of all, the reaction in the ionic liquid solvent is biphasic with no detectable... 

The effect of catalysis by trifluoroacetic acid on chlorination in carbon tetrachloride has also been determined272. For 1,2,4,5-tetramethylbenzene, with low concentrations of catalyst, the order in catalyst is three-halves, but for toluene (which requires a higher concentration) the order is mixed three- and five-halves the indication is, therefore, that a minimum of three catalyst monomers (or one monomer and one dimer) are necessary. Since trifluoroacetic acid is very likely to be dimeric in carbon tetrachloride, the concentration of monomer is pro-... 

Simulated0 kinetic data for equilibration in the reaction Dimer 2Ph,C or A t 2P in toluene... 

This has just the A 2P form to which the earlier equations apply. Consider for a moment a hypothetical experiment (we shall shortly see the real one). Imagine that the dimer (= A), initially present alone, equilibrates in toluene, the reaction being followed by the increase of absorbance as Ph3C forms. 

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