Crystal aromatic hydrocarbons

Iodine solutions. Dissolve i crystal of iodine in diethyl ether and note the brown colour. Aromatic hydrocarbons e.g. benzene) give purple solutions. 

Pitches can be transformed to a mesophase state by further chemical and physical operations. Heat treatment of conventional pitches results in additional aromatic polymeriza tion and the distillation of low molecular weight components. This results in an increase in size and concentration of large planar aromatic molecular species whereupon the precursor pitch is transformed to a mesophase state exhibiting the characteristics of nematic Hquid crystals (1). Additional heat treatment converts the mesophase pitch to an infusible aromatic hydrocarbon polymer designated as coke. 

With substances that give up an electron more readily than aromatic hydrocarbons, such as potassium, nickel carbonyl, cyanide ion, or iodide ion, complete transfer of an electron occurs and the TCNE anion radical is formed (11). Potassium iodide is a particulady usefiil reagent for this purpose, and merely dissolving potassium iodide in an acetonitrile solution of TCNE causes the potassium salt of the anion radical to precipitate as bronze-colored crystals. 

For aromatic hydrocarbon molecules, in particular, the main acceptor modes are strongly anharmonic C-H vibrations which pick up the main part of the electronic energy in ST conversion. Inactive modes are stretching and bending vibrations of the carbon skeleton. The value of Pf provided by these intramolecular vibrations is so large that they act practically as a continuous bath even without intermolecular vibrations. This is confirmed by the similarity of RLT rates for isolated molecules and the same molecules imbedded in crystals. 

In Table II there are given the available experimental values of the principal susceptibilities of aromatic hydrocarbon molecules, from the papers of Krishnan and his collaborators.111 lc 10 It should be mentioned that in some cases the values have been obtained from crystal susceptibilities in a straightforward manner, with... 

Phenol (C5H5OH) or carboUc acid is an aromatic hydrocarbon derived originally from coal tar, but prepared synthetically in a process that utilizes monochlorobenzene as a starting point. Ninety-eight percent phenol appears as transparent crystals, while liquefied phenol consists of 88% USP solution of phenol in water. 

The thienothienoimidazolium salts 29 were prepared by the reaction of thiophanes 362 with HX (X = halogen) and crystallization from solvents selected from ketones, aromatic hydrocarbons, and halohydrocarbons. l-(—)-3,4-(l, 3 -dibenzyl-2 -ketoimidazolido)-2-(u -ethoxypropyl)tetrahydrothiophene 362 was reacted with HBr at 99-103 °G for 2h and crystallized from methyl-Tro-butyl ketone to give l-(—)-3,4-(T,3 -dibenzyl-2 -ketoimidazolido)-l,2-trimethyle-nethiophanium bromide 29 (95%, 98.7% purity) (Scheme 75) <2001JAK100477>. 

Reaction of the primary phosphane Bu3SiPH2 If with MgBu2 furnishes the solvent-free hexameric cluster 17 (Eq. 10) (47). Yellow crystals, have been isolated in 39% yield, which are thermochromic. The NMR spectrum, especially the 31P NMR signal at S = -263.8, suggested that the molecule prefers a high symmetry or dissociates rapidly on the NMR time scale. Since 15 is highly soluble in aromatic hydrocarbons even at low temperature and free of metal oxide, it can thus be regarded as a valuable source of phosphandiide, that is, for nucleophilic RP2 transfer reactions. 

Srivastava, V.K., P.K. Srivastava, and U.K. Misra. 1985. Polycyclic aromatic hydrocarbons of coal fly ash analysis by gas-liquid chromatography using nematic liquid crystals. Jour. Toxicol. Environ. Health 15 333-337. 

P.R.14 provides an intense, hghtfastbordeaux shade, which is much yellower than that of P.R.12. Like P.R.12, it also possesses two crystal modifications. Again, the commercially available form is thermodynamically unstable but, in contrast to P.R.12, conversion to the stable modification, which is technically less interesting because of its poor lightfastness, requires somewhat of an effort. It is facilitated, for instance, by aromatic hydrocarbon and ketone solvents. 

The -modification as a rule evolves as a more coarse-grained material than the a-phase. It is prepared by milling the crude Copper Phthalocyanine Blue with salt in the presence of a crystallization stimulating solvent. Aromatic hydrocarbons, esters, or ketones are normally used. 

The same tt-SCF force field was used for calculations on 2,6-diphenylhomotropUidene (51). In the crystal, this molecule exists in the chair form, which proved to be the global energy minimum. The MM calculations of nonbenzonoid aromatic hydrocarbons have been reviewed elsewhere (lOd). 

Cyanation of aromatic hydrocarbons, also a carbon-carbon coupling reaction, is achieved in the case of anthracene in MeCN-Et4NCN to yield 54% 9,10-dicyanoanthracene [165]. The cyanation is simplified when it is carried out in an emulsion system (aqueous sodium cyanide, dichloromethane, and TBAHSO4). Its synthetic utility in this mode has been demonstrated for the preparation of 4-alkoxy-4-cyanobiphenyls, a class of liquid crystals [166]. 

Janini, GM., Johnston, K., and Zielinski, W.L., Use of a nematic liquid-crystal for gas-liquid-chromatographic separation of poly aromatic hydrocarbons, Anal Chem., 47, 670, 1975. 

Janini, GM., Muschik, G.M., Schroer, J.A., and Zielinski, W.L., Gas-liquid-chromatographic evaluation and gas-chromatography mass spectrometric application of new high-temperature hquid-crystal stationary phases for polycyclic aromatic hydrocarbon separations. Ana/. Chem., 4S, 1879, 1976. 

Janini, G.M., Muschik, G.M., andZielinski, W.L., A,A -i>w[para-butoxybenzylidene)-alpha,alpha -bi-para-toluidine—thermally stable liquid-crystal for unique gas-liquid-chromatography separations of polycyclic aromatic-hydrocarbons, Anal Chem., 48, 809, 1976. 

The physical properties of many macrocyclic polyethers and their salt complexes have been already described. - Dibenzo-18-crown-6 polyether is useful for the preparation of sharpmelting salt complexes. Dicyclohexyl-18-crown-6 polyether has the convenient property of solubilizing sodium and potassium salts in aprotic solvents, as exemplified by the formation of a toluene solution of the potassium hydroxide complex (Note 13). Crystals of potassium permanganate, potassium Lbutoxide, and potassium palladium(II) tetrachloride (PdClj + KCl) can be made to dissolve in liquid aromatic hydrocarbons merely by adding dicyclohexyl-18-crown-6 polyether. The solubilizing power of the saturated macrocyclic polyethers permits ionic reactions to occur in aprotic media. It is expected that this [)ropcrty will find practical use in catalysis, enhancement of... 

The adduct formed by two lithium atoms with polycondensed aromatic hydrocarbons crystallizes with two solvating molecules of TMEDA. The structure of the crystals derived from naphthalene (73) and anthracene (74) was elucidated by XRD. This arrangement of the unsolvated lithium atoms, in 7 -coordination fashion on the opposite sides of two contiguous rings, was found by MNDO calculations to be the most favorable one for naphthalene, anthracene and phenanthrene (75) . 

Most of the 2-amino-4H-pyrans are colorless, pale-yellow, or pale-cream crystals with high melting points. They are readily soluble in aromatic hydrocarbons, alcohols, acetone, acetonitrile, chloroform, DMF, and DMSO, and nearly insoluble in hexane and water. 

To reveal factors which influence activities of acid-base catalysts in alkylation and isomerization is the challenge to activity in this field. Q he greatest amount of work has been done in connection with the effect of para-selectivity, which is observed in alkylation of aromatic hydrocarbons on ZSM-5 type zeolites [1]. This effect has been explained by a number of authors either by the influence of diffusion factors [2,3] or by the isomerizing activity of the external surface of zeolite crystals [4]. In refs. [5,6] and especially in ref.[7] the para-selective effect of ZSM-5 type zeolites is shown to be due to decreasing their isomerizing activity becaiase of the decrease in the concentration of strong protic centres as a result of modifiers introduced. Para-selective effect is related to the action of chemical factors. However, in... 

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