Benzene rings disubstituted

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... 

Chemical equivalence atomic nuclei in the same chemical environment are chemically equivalent and thus show the same ehemieal shift. The 2,2 - and 3,3 -protons of a 1,4-disubstituted benzene ring, for example, are ehemically equivalent because of molecular symmetry. 

Since two quaternary atoms and four CH atoms appear in the C NMR spectrum, the latter with a benzenoid coupling constant of 7-9 Hz, this is a disubstituted benzene ring, and the C signal with 5c = 162.2 fits a phenoxy C atom. The keto carbonyl (5c = 204.9) and methyl (5c = 26.6) resonances therefore point to an acetyl group as the only meaningful second substituent. Accordingly, it must be either o- or m-hydroxyacetophenone A or B the para isomer would show only four benzenoid C signals because of the molecular symmetry. 

Adding these substituent effects gives the following calculated shift values (as compared with the observed values in parentheses) for C-1 to C-4 of the pura-disubstituted benzene ring in A and B ... 

III. In tropeines containing a disubstituted benzene ring, those in which the replacing groups occupy the pam-position have the least mydriatic action thus 0- and m-hydroxybenzoyltropeines are active, but not the p-isomeride. 

Electrophilic substitution of a disubstituted benzene ring is governed by the same resonance and inductive effects that affect monosubstituted rings. The only difference is that it s now necessary to consider the additive effects of two different groups. Tn practice, this isn t as difficult as it sounds three rules are usually sufficient. 

Problems arise in the preparation of substituted l//-azepines with (alkoxycarbonyl)nitrenes as nitrene attack on a mono- or disubstituted benzene ring is not generally regioselective, and with toluene, 04 34-136139 144 o- and p-xy ienes,134-139 p-cresoi,134 chlorobenzene104-134 136 and biphenyl,104 136 mixtures of 1//-azepine-1-carboxylates of undetermined composition are produced. 

The appearance of a 4 proton symmetrical pattern in the aromatic region near 5 7.9 and 6.6 ppm is strongly indicative of a para disubstituted benzene ring. This is confirmed by the presence of two quaternary resonances at 5 152 and 119 ppm in the spectrum and two CH resonances at 5 131 and 113 ppm. 

Note that the presence of a para disubstituted benzene ring also accounts for the element of symmetry identified above. The triplet of 3H intensity at approximately 5 1.4 and the quartet of 2H intensity at approximately 5 4.3 have the same spacings of 1.1 mm. On this 100 MHz NMR spectrum, 100 Hz (1 ppm) corresponds to 16.5 mm so the measured splitting of 1.1 mm corresponds to a coupling of 6.7 Hz that is typical of a vicinal coupling constant. The triplet and quartet clearly correspond to an ethyl group and the downfield shift of the CH2 resonance (5 4.3) indicates that it must be attached to a heteroatom so this is possibly an -O-CH2-CH3 group. 

After the optimization of the conditions for the production of o-bromophenyl-lithium to —78°C with a 0.8 s residence time, the scope was extended to sequential Br-Li exchange of both bromine substituents on the benzene ring and the reaction with electrophiles to form o-disubstituted benzene rings. This was done in a four-step reaction in one flow using four-linked microreactors (MRi ). For the second lithiation, the temperature of 0°C was sufficient, which was expected since the aryllithium intermediate is more stable than o-bromophenyllithium. 

C-H out of plane deformation showing 1,2-disubstituted benzene ring. 

The structure of cleistopholine (154), was suggested by its high-resolution mass spectrum and its IR and NMR spectra (77). The H-NMR spectrum indicated the presence of a nearly symmetrically ortho-disubstituted benzene ring and a 2,3-disubstituted 4-methylpyridine ring that could best be accommodated by the 4-methyl-l-azaanthra-9,10-quinone structure. Complete assignment of its... 

Figure 2.6. 1H NMR spectra of disubstituted benzene rings [CDCI3, 25 °C, 200 MHz], (a) o-Nitrophenol (3) (b)...

Misumi et al. by this method bridged a cyano-disubstituted benzene ring with aliphatic chains of 8 to 10 carbon atoms as in 187a/b [64]. The yield of the less-strain phane having the 10-membered bridge is higher than for the more strained derivative. 

There are two acceptable ways of naming the three positional isomers that are possible for disubstituted benzene rings. The substituent... 

What happens in electrophilic aromatic substitution when a disubstituted benzene ring is used as starting material To predict the products, look at the directing effects of both substituents and then determine the net result, using the following three guidelines. 

Meta isomer (Section 17.3B) A 1,3-disubstituted benzene ring. Meta substitution is abbreviated as m-. 

AA ) and 3,y-(X,X ) protons of a 1,4-disubstituted benzene ring such as 4-nitroanisole are not magnetically equivalent, because the 2-proton A shows an ortho coupling with the 3-proton X i J= 7-8 Hz), but displays a different para coupling with the 3 -proton 0.5-lHz). This is there-... 

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