Benzene, alkylation structure

In an elegant series of reactions, it has been demonstrated that 1//-azepines can be forced into adopting the benzene imine structure 8 by bridging the 2- and 7-positions with a trimethyl-ene chain.61 The length of the alkyl chain, however, is critical and the tetramethylene derivative exists solely as the 2,7-bridged l//-azepine (see Section 3.1.1.4.1.3.). 

Ortho photocycloadditions of benzene derivatives to maleic anhydride have been tabulated in Table 1. Only the structures of the primary ortho adducts are given, but these are not the isolated adducts They always undergo endo [2 + 4] cycloaddition with maleic anhydride, yielding 1 2 adducts. An interesting feature to be seen from Table 1 is that substituents on the benzene (alkyl, phenyl, or halogen) always turn up at the position most remote from the site of addition. In view of the different nature of these substituents, it seems that steric rather than electronic factors are responsible for this regioselectivity. 

Carbon nanotubes are a new generation of sorbent materials with great potential for selective adsorption and shape selective separation. We report the studies on the MD simulation of structure of the carbon nanotube and the dynamic behaviour of aromatic molecules such as benzene, alkylated benzenes as well as alkylated naphthalenes[35]. The interest is to design effective molecular sieves for the bulk separation of hydrocarbon molecules of industrial importance. 

Aromatic hydrocarbons are of special commercial importance. The benzene ring structure, with six carbons and three double bonds, is the fundamental aromatic unit. This molecule can have one or more hydrogen substitutions with side chains, resulting in alkyl benzenes (e.g. the TEX in BTEX [benzene, toluene, ethylbenzene and xylene]) or two or more aromatic rings may be fused together to form polycyclic aromatic hydrocarbons (PAHs). 

Crystalline borosilicate molecular sieves have been the object of an intensive investigation effort since they were reported in the open literature at the Fifth International Conference on Zeolites by Taramasso, et al. (1) A wide range of structures containing framework boron have been synthesized. The physical properties of these borosilicate molecular sieves have been studied by such techniques as X-ray diffraction, infrared and nuclear magnetic resonance spectroscopies, and temperature programmed desorption of ammonia. In addition, the catalytic performance of borosilicate molecular sieves has been reported for such reactions as xylene isomerization, benzene alkylation, butane dehydroisomerization, and methanol conversion. This paper will review currently available information about the synthesis, characterization, and catalytic performance of borosilicate molecular sieves. 

Currently, it is known that high thermal and thermal-oxidative resistance in polyimide requires purely aromatic systems and that alkyl structures in the backbone or as substituents interfere with resistance. It is also assumed that further benzene rings in the backbone or hetero members between the benzene rings reduce resistance. Fluorine addition, on the other hand, improves resistance. Chlorine substitution results in improved resistance however, the results are ambiguous [572]. 

Because of the structural requirements of the bielectrophile, fully aromatized heterocycles are usually not readily available by this procedure. The dithiocarbamate (159) reacted with oxalyl chloride to give the substituted thiazolidine-4,5-dione (160) (see Chapter 4.19), and the same reagent reacted with iV-alkylbenzamidine (161) at 100-140 °C to give the 1 -alkyl-2-phenylimidazole-4,5-dione (162) (see Chapter 4.08). Iminochlorides of oxalic acid also react with iV,iV-disubstituted thioureas in this case the 2-dialkylaminothiazolidine-2,4-dione bis-imides are obtained. Thiobenzamide generally forms linear adducts, but 2-thiazolines will form under suitable conditions (70TL3781). Phenyliminooxalic acid dichloride, prepared from oxalic acid, phosphorus pentachloride and aniline in benzene, likewise yielded thiazolidine derivatives on reaction with thioureas (71KGS471). 

However, other studies on the nitration of a series of 3-methyl- and 3-ethyl-1,2-benzisoxazoles have shown that a mixture of the 5-nitro and 5,7-dinitro derivatives is formed (77IJC(B)1058, 77IJC(B)1061). The effect of substituents in the benzene ring is also of interest. If the 5-position is blocked, e.g. by a chloro group or by alkyl groups, nitration then occurs at the 4-position. 3-Alkyl-7-chloro and 3,7-dialkyl derivatives result in the formation of the appropriate 5-nitro derivative. The isomeric 3-alkyl-6-chloro- and 3,6-dialkyl-1,2-benzisoxazoles yield a mixture of the 5-nitro and 5,7-dinitro compounds. Both H NMR measurements and alternate syntheses were used in establishing the structures of these substitution products. 

The initial step is the coordination of the alkyl halide 2 to the Lewis acid to give a complex 4. The polar complex 4 can react as electrophilic agent. In cases where the group R can form a stable carbenium ion, e.g. a tert-buiyX cation, this may then act as the electrophile instead. The extent of polarization or even cleavage of the R-X bond depends on the structure of R as well as the Lewis acid used. The addition of carbenium ion species to the aromatic reactant, e.g. benzene 1, leads to formation of a cr-complex, e.g. the cyclohexadienyl cation 6, from which the aromatic system is reconstituted by loss of a proton ... 

The procedure used in the preceding sections for cyclopropane serves equally well in the analytic determination of the numbers of structure and stereoisomeric compounds which obtain when essentially different radicals of valence one or alkyl radicals are substituted in the basic compound. We have to assume, however, that there is enough information on the basic compound to determine the three groups discussed in Sec. 56. This is certainly the case for the most important basic compounds, benzene and naphthalene. I omit the formulation of rules which are obvious in the preceding example. 

Benzene and alkyl-substituted benzenes can be hydroxylated by reaction with H2O2 in the presence of an acidic catalyst. What is the structure of the reactive electrophile Propose a mechanism for the reaction. 

Popova and colleagues47 carried out TLC of oxidation products of 4,4 -dinitrodiphenyl sulphide (the sulphoxide and sulphone) on silica gel + a fluorescent indicator, using hexane-acetone-benzene-methanol(60 36 10 l) as solvent mixture. Morris130 performed GLC and TLC of dimethyl sulphoxide. For the latter, he applied a 6% solution of the sample in methanol to silica gel and developed with methanol-ammonia solution(200 3), visualizing with 2% aqueous Co11 thiocyanate-methanol(2 1). HPLC separations of chiral mixtures of sulphoxides have been carried out. Thus Pirkle and coworkers131-132 reported separations of alkyl 2,4-dinitrophenyl sulphoxides and some others on a silica-gel (Porosil)-bonded chiral fluoroalcoholic stationary phase, with the structure ... 

Examinations of the connection between the chemical structure of alkylaryl sulfates and their physical-chemical properties show that solubility, aggregations and adsorption behavior, foam behavior and consistency are determined by the following structural elements the length of the alkyl chain, the position at which the benzene ring is connected to the alkyl chain, and the substitution pattern of the benzene ring [187,188]. 

Secondly, the rates and modes of reaction of the intermediates are dependent on their detailed structure. For example, the stability of the cation radical formed by the oxidation of tertiary aromatic amines is markedly dependent on the type and degree of substitution in the p-position (Adams, 1969b Nelson and Adams, 1968 Seo et al., 1966), and the rate of loss of halogen from the anion radical formed during the reduction of haloalkyl-nitrobenzenes is dependent on the size and position of alkyl substituent and the increase in the rate of this reaction may be correlated with the degree to which the nitro group is twisted out of the plane of the benzene ring (Danen et al., 1969). 

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