Monosubstituted aromatic molecules

When a substituent is introduced directly into an aromatic molecule, it may enter into certain of the available positions more readily than into others. This phenomenon of orientation has been exhaustively studied, and empirical rules have been found which describe the experimental results fairly satisfactorily. In a monosubstituted benzene CeHjR, for example, the introduction of... 

Figure 1. Nonlinearity of some monosubstituted aromatic molecules in terms of their dipole moments (ir electron contributions).

Some substituents induce remarkably different electronic behaviors on the same aromatic system (8). Let us consider, for example, the actions of substituents on an aromatic electron system. Some substituents have a tendency to enrich their electronic population (acceptors), while others will give away some of it (donors). Traditionaly, quantum chemists used to distinguish between long range (mesomeric) effects, mainly u in nature, and short range (inductive) effects, mainly a. The nonlinear behavior of a monosubstituted molecule can be accounted for in terms of the x electron dipole moment. Examples of donor and acceptor substituents can be seen on figure 1. 

Answer Since we are limited to starting with monosubstituted cyclic molecules we have the option of adding the carbons to the chlorinated ring or adding the Cl to the aromatic alcohol. In the lab it is easier to do the former, so we shall proceed along that line. Thus, we have to add carbons. 

In toluene, as well as with many other monosubstituted benzenes, the substitution group (methyl, in the case of toluene) acts as an electron donor. This counters the electron-withdrawing effect of the previously substituted nitro groups and allows higher local nitronium ion activity, thus allowing a much easier trinitration step. This is the key, then, to inexpensive synthesis of trinitro-aromatic explosives. Figure 3.5 is the TNT molecule, the first, and most important (as far as quantity of production goes) of the monosubstituted TNBs. 

Thermal Decomposition of Sulfinate (XVI). A solution of 0.12 mmol of sulfinate (XVI) in 1 mL of o-dichlorobenzene was heated at 150°C. In the liquid chromatograms several peaks rose and disappeared during the reaction. Three main products were isolated 4-methoxy-2,6-diphenyl-phenol (Vila) was identified by its ir spectrum thiosulfonate (IXVIII), the vmax 1200 s (S02), 750 s, and 700 s cm-1 (aromatic monosubstitution), (mass spectrometry parent peak (M) m/e 306, peak m/e 242 (M-S02), m/e 105 (CeH5C2H4 fragment), and a molecule ion peak m/e 136, which was assigned to sulfide XX) and sulfonate XIX (the vmax 2830 w (OCH3), 1200 s (S02), and strong bands between 700 and 800 cm-1 (two types of aromatic substitution) mass spectrometry parent peak (M) m/e 444, peak m/e 380 (M-S02)). 

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