Aromatic compounds disubstituted benzenes

Experimental Verification. The changes of capacity factor values k with (3-CD concentration in the mobile phase solution are illustrated in Figure 1 as the behavior of methylphenobarbital enantiomers on RP-18 columns (26). The similar influence of CD on k values was observed for all the studied compounds ( disubstituted benzenes, mandelic acid and its derivatives, some aromatic aminoacids, some barbiturates and hydantoins)(17-19,21-26,28). o(- or -CD additions were always followed by a decrease in the apparent capacity factor (k ) values. These results suggest that the adsorption... 

Although there are a wide variety of indole ring syntheses (25), most of the more useful examples fall within a small number of groups. Indole syntheses usually start with an aromatic compound, either monosubstituted or ortho-disubstituted. Those which begin with a monosubstituted starting material must at some point effect a substitution of the benzene ring. 

The term aromatic is used for historical reasons to refer to the class of compounds related structurally to benzene. Aromatic compounds are systematically named according to TUPAC rules, but many common names are also used. Disubstituted benzenes are named as ortho (1,2 disubstituted), meta (1,3 disub-stituted), or para (1,4 disubstituted) derivatives. The C6H5- unit itself is referred to as a phenyl group, and the Cb f5CH2— unit is a benzyl group. 

Smith and coworkers have screened the solid catalysts for aromatic nitration, and found that zeolite (3 gives the best result. Simple aromatic compounds such as benzene, alkylbenzenes, halogenobenzenes, and certain disubstituted benzenes are nitrated in excellent yields with high regioselectivity under mild conditions using zeolite (3 as a catalyst and a stoichiometric quantity of nitric acid and acetic anhydride.11 For example, nitration of toluene gives a quantitative yield of mononitrotoluenes, of which 79% is 4-nitrotoluene. Nitration of fluorobenzene under the same conditions gives p-fluoronitrobenzene exclusively (Eqs. 2.1 and 2.2)... 

Most of the fairly extensive photochemistry of aromatic compounds has not been studied in sufficient detail to permit disentanglement of singlet and triplet mechanisms. Theoretical calculations indicate that the pattern of substituent effects on side-chain reactions of excited disubstituted benzenes should be quite different from that observed in the ground states of the molecules. One problem associated with these predictions is the question of whether or not they are appropriate for triplets as well as for corresponding singlet excited states. Consider the following system ... 

Substituted aromatic compounds are named using the suffix -benzene. Thus, C6H5Br is bromobenzene, C6H5CH3 is methylbenzene (also called toluene), C6H5N02 is nitrobenzene, and so on. Disubstituted aromatic compounds are named using one of the prefixes ortho-, meta-, or para-. An ortho- or o-disubstituted benzene has its two substituents in a 1,2 relationship on the ring a meta- or m-disubstituted benzene has its two substituents in a 1,3 relationship and a para- or p-disubstituted benzene has its substituents in a 1,4 relationship. When the benzene ring itself is a substituent, the name phenyl (pronounced fen-nil) is used. 

Name and write the structures for aromatic compounds, especially monosubstituted and disubstituted benzenes and toluenes. 

Donor-substituted benzenes and electrophiles should produce mixtures of para- and orf/zo-disubstituted aromatic compounds, in which the /zara-disubstituted product is formed in a greater amount. Only traces of the /neto-disubstitution product are expected, even though a donor-substituted benzene is substituted faster at the meta-C atom than benzene itself at any of its C atoms. 

The substitution product should primarily be the mefa-disubstituted aromatic compound. Among the by-products, the orf/zo-disubstituted benzene should predominate, while practically no />ara-product is expected. 

The rate constants for the reactions of eaq with aromatic compounds depend very strongly on the substituent. Benzene itself has a relatively low reactivity, k = T4 x 107 M -1 s 1, phenol and aniline are even less reactive, but substituents such as CN, Br, and N02 increase the rate constant almost to the diffusion controlled limit. The rate constants for several series of mono- and disubstituted benzenes were correlated with Hammett s substituent constants a and showed good linear relationships. 

For disubstituted chlorides and bromides of benzene and of ethylene, one of us f has found that the moment of the chloro-derivatives is larger than that of the bromo-derivatives. In these aliphatic compounds the dipole moment of the chloro- and bromo-derivatives is greater than for the hydroxyl-derivative, in contradistinction to the aromatic compounds, where the dipole moment of the hydroxyl derivative is greater than that of the chloro- and bromo-derivatives. 

Compound A contains chlorine (M 138/140 3 1) and that fits CgHyCl, it still has the 1.4-disubstituted benzene ring (four aromatic Hs), and it is an alkene (IR 1640 cm ) with three hydrogen atoms on the double bond ( h 6.5, 5.5, and 5.1). We can write the structure immediate " as there is no choice. 

Substituent Effects. - The C NMR substituent-induced chemical shifts (SCS) of aromatic carbons in 1,4-disubstituted benzenes were correlated with inductive and mesomeric effects, expressed in ai and qr (NMR) scales, and with charge alterations (Aq) provoked by introducing a new substituent (X) at position Cl. 105 different compounds with groups attached to Cl (X) and C4 (Y) in a sequence NMe2, NH2, OMe, F, Cl, Br, Me, H, CF3, CN, C(0)0Et, C(0)Me, NO2 and CHO were studied. ... 

P Tomasik, TM Krygowski, and T Chellathurai. The Hammett-Type Approach to the Substituent Effects in the UV Absorption Spectra of Aromatic Compounds. III. The Spectra of orf/io-Disubstituted Benzene Derivatives. Bull. Acad. Polon. Ser. Set Chim. 22 1065-1074, 1974. 

Benzene. The earliest work in directed metalation was done on the benzene system in the early 1930s (3). That the benzene ring was the most promising system for the exploitation of this reaction appears logical since it was by far the most examined aromatic system at that time. Not only have the largest number of directing substituents been successfully demonstrated for this system, but in all probability the demand for a convenient route to a specific polysubstituted aromatic compound will be highest for this system. In all cases examined, directed metalation of a monosubstituted benzene has yielded almost exclusively ortho metalation, with only ortho-disubstituted products obtained (Reaction 1). With... 

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