Disubstituted benzene derivatives

OH groups are in the para or 1,4 position to each other. This use of the prefix is confined to disubstituted benzene derivatives in such cases as para-hydrogen and paraldehyde the prefix has no uniform structural significance and is always written in full. 

A brief account of aromatic substitution may be usefully given here as it will assist the student in predicting the orientation of disubstituted benzene derivatives produced in the different substitution reactions. For the nitration of nitrobenzene the substance must be heated with a mixture of fuming nitric acid and concentrated sulphuric acid the product is largely ni-dinitrobenzene (about 90 per cent.), accompanied by a little o-dinitrobenzene (about 5 per cent.) which is eliminated in the recrystallisation process. On the other hand phenol can be easily nitrated with dilute nitric acid to yield a mixture of ortho and para nitrophenols. It may be said, therefore, that orientation is meta with the... 

The prefix ortho signifies a 1 2 disubstituted benzene ring meta signifies 1 3 disubstitu tion and para signifies 1 4 disubstitution The prefixes o m and p can be used when a substance is named as a benzene derivative or when a specific base name (such as ace tophenone) is used For example... 

Partial rate factors may be used to estimate product distributions in disubstituted benzene derivatives The reactivity of a particular position in o bromotoluene for example is given by the product of the partial rate factors for the corresponding position in toluene and bromobenzene On the basis of the partial rate factor data given here for Fnedel-Crafts acylation predict the major product of the reaction of o bromotoluene with acetyl chlonde and aluminum chloride... 

As appropriately substituted o-disubstituted benzene derivatives are feadily available, this procedure has found widespread application in the synthesis of benzo-fused flve-membered heterocycles. Examples abound in the various chapters in these volumes and the following few examples illustrate the general trend. 

Although the application of the Hammett equation to side-chain reactions of disubstituted benzene derivatives (1) is relatively straightforward, the introduction of a heteroatom somewhere in the aromatic... 

The problems encountered in any attempt to treat the transmission of the effects of one substituent in a disubstituted heterocycle through the heterocyclic nucleus to a reaction site in the other substituent (i.e. the side-chain) are enormous, and it is consequently not surprising that relatively little work has been done in this area. First, while in benzene derivatives there are three positions, i.e. three relations between substituent and reacting side-chain to be considered, the number of complexities is much greater in heterocycles. Thus, e.g., in pyridine alone, after elimination of the orientations involving a vicinal relationship between substituent R and the side-chain Y to which no Hammett-type relation is likely to be applicable, the following cases should be considered ... 

Disubstituted benzene derivatives containing electrophilic substituents C6H3... 

The para-disubstituted benzene derivative, 13, of Fig. 11 has two groups of equivalent bonds to hydrogen the ones to hydrogens 1 and 4, and those to hydrogens 2 and 3. If only one C—H bond from the first group in this molecule is to be broken, it... 

Cyclohexadienylidenes, disubstituted at the 4-position are expected to be kinetically more stable than the parent carbene, however, the rearrangement to benzene derivatives is still very exothermic. The gas phase chemistry of 4,4-dimethyl-2,5-cyclohexadienylidene Is was investigated by Jones et al.100,101 The gas phase pyrolysis of the diazo compound 2s produces a mixture of p-xylene and toluene, and by crossover experiments it was demonstrated that the methyl group transfer occurs intermolecularly via free radicals. Thus, the pyrolysis of a mixture of the dimethyl and the diethyl derivative 2s and 2t... 

Basketter, D.A., and Goodwin, B.F.J., Investigation of the prohapten conceptL cross reaction between 1,4-disubstituted benzene derivatives in the guinea pig. Contact Dermatitis, 19, 248, 1988. 

The reaction of the chloro ester 1-Me with 1,2-dinucleophilic 1,2-disubstituted benzene derivatives 161 in most cases gave the benzene-annelated six-member-ed heterocycles 162 in moderate yield (Scheme 50) [22b, 26,73]. The course of the domino-Michael addition-cyclization is also very sensitive to the nature of the base and the reaction conditions applied. Thus, only the primary Michael adducts... 

Statistical analysis within a Ti-perturbation model and comparison with 1,4-disubstituted benzene derivatives supports the above sequence of increasing acceptor effect of substituents. The substituent effect is observed for the other series such as R (PR2) , R (P+R3) and R (PyR2) , where Y = O, S, Se, NR and n = 1,2. 

When there are two or more substituents on a benzene ring, position isomerism arises. Thus there are three possible isomeric disubstituted benzene derivatives according to whether the substituents have the 1,2, 1,3, or 1,4 relationship. The isomers commonly are designated as ortho, meta, and para (or o, m, and p) for the 1,2-, 1,3-, and 1,4-isomers, respectively. The actual symmetry of the benzene ring is such that only one 1,2-disubstitution product is found, despite the fact that two would be predicted if benzene had the 1,3,5-cyclohexatriene structure ... 

Benzene derivatives with two nucleofuges have been used in the preparation of polymeric materials with varying degrees of success. Poly(l,4-phenylene sulfide) has been prepared by condensation of p-di-chlorobenzene with sodium sulfide,99,100 and in a related process, diazonium ions have been shown to initiate the polymerization of p-halobenzenethiolate ions.101 In a preliminary study, poorly characterized polymers were obtained from reaction of equimolar amounts of p-dihalobenzenes and the enolate ions from ketones in the presence of excess base. When an excess of the ketone enolates was used, the normal p-disubstituted derivatives were formed.102... 

This question could be answered more easily if we knew that the C6C3 units conformed with the principle of additivity. This principle can be formulated as follows. If the introduction of each of two substituents alters the free energy of activation at a particular position by amounts x and y, the presence of both substituents would alter the free energy of activation by an amount (x + y). If this relationship holds, it allows one to predict the reactivities of the individual positions in disubstituted benzene derivatives from the rate data obtained for the corresponding monosubstituted ones. The partial rate factor for a given position of a... 

Felix, Dunogues and Calas98-101 have extended this strategy such that a range of disubstituted benzene derivatives 74 can be regiospecifically synthesized starting from the readily accessible o-, m- or p-bis(trimethylsilyl)benzenes 73 (equation 38). 

The primary ortho adducts formed from benzene derivatives and acetylenes are derivatives of bicyclo[4.2.0]octa-2,4,7-triene. These products usually are not isolated but isomerize during the irradiation to cyclooctatetraenes [58,59,68,72], From combinations of hexafluorobenzene and pentafluoroalkoxybenzenes with various disubstituted acetylenes, however, the isolation of relative stable primary ortho adducts has been reported [65-67], In Scheme 46, the products of the photochemical reaction of hexafluorobenzene with but-2-yne are shown [67],... 

The nomenclature of benzene derivatives is described in Sec. 4.6. Common names and structures to be memorized include those of toluene, styrene, phenol, aniline, and xylene. Monosubstituted benzenes are named as benzene derivatives (bromobenzene, nitrobenzene, and so on). Disubstituted benzenes are named as ortho- (1,2-), meta- (1,3-), or para- (1,4-), depending on the relative positions of the substituents on the ring. Two important groups are phenyl (C6H5-) and benzyl (C6H5CH2-). 

E. Rearrangements of Ethers Containing Disubstituted Allyl Groups, Benzene Derivatives... 

BASF in Ludwigshafen, Germany, and university partners reported the nitration of several disubstituted benzene derivatives using a capillary-flow microreactor [22], The exact nature of these species, however, was not disclosed. 

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