Mono-substituted aromatics

For the Birch reduction of mono-substituted aromatic substrates the substituents generally influence the course of the reduction process. Electron-donating substituents (e.g. alkyl or alkoxyl groups) lead to products with the substituent located at a double bond carbon center. The reduction of methoxybenzene (anisole) 7 yields 1-methoxycyclohexa-1,4-diene 8 ... 

Witte, F., Urbanik, E., Zetzsch, C. (1986) Temperature dependence of the rate constants for the addition of OH to benzene and to some mono substituted aromatics (aniline, bromobenzene, and nitrobenzene) and the unimolecular decay of the adducts. Kinetics into a quasi-equilibrium. J. Phys. Chem. 90, 3251-3259. 

Acidic chloroaluminate ionic liquids are able to generate acylium ions and are therefore ideally suited to Friedel-Crafts reactions. Acylation of mono-substituted aromatic compounds in acidic chloroaluminate ionic liquids leads almost exclusively to substitution at the 4-position on the ring [9] (Scheme 10.8). 

The initial product 5 of the electrophilic aromatic substitution step is unstable and easily hydrolyzes to yield the aromatic aldehyde 3 as the final reaction product. With mono-substituted aromatic substrates the para-substituted aldehyde is formed preferentially. 

The differentiation is easily made by noting the characteristic absorption bands corresponding to the aromatic ring system around 1600-1450cm-1 and 850-660cm-1, and the characteristic pattern in the overtone region around 2000-1800 cm- The origin of these absorptions is discussed in detail below their presence in this spectrum clearly shows that the structure is a mono-substituted aromatic compound. 

Electrophilic Substitutions of Mono-substituted Aromatic Rings... 

The formation of di- and tri-alkyl aromatics and b henyls from their aromatic precursor is a consecutive reaction, in A hich first the mono-substituted aromatic conopound is formed which subsequently reacts to form the di-alkyl compund. This was observed in the shape selective ethylation of bphenyl [91] isopropjdation of naphthalene [92] over H-Mordenite and the isopropylation of napthalene over HY [63], Therefore, if a dialkyl-isomer is the desired product, the reaction conditions (reaction time/readence time, partial pressures and tenperature) have to be optimized to obtain the the maximum yield of this de ed product. With shape selective catalysts the formation of poly-substituted aromatic compounds can be suppressed because they are not able to diffuse out of the channels of the zeolites [63]. 

In disubstituted aromatic systems, the position of the second substituent with respect to the first functional group is indicated either by a number, with the first group having the 1 position, or by the prefix ortho, meta or para indicating the 2, 3 or 4 positions, respectively. These prefixes are often abbreviated to o, m orp, respectively. If a mono-substituted aromatic compound is attacked at a ring carbon that already bears a substituent, then this is called ipso attack. 

Industrially manufactured polystyrene, polymerized with radical initiators, exists mainly as the atactic polymer. The IR spectrum of this form of polystyrene features bands consistent of a mono-substituted aromatic compound. In addition to the normal aromatic absorptions, such as the C—H stretching between 3110 and 3000 cm , and the characteristic ring vibrations at approximately 1600 and 1500 cm (1601 and 1493 cm for polystyrene), the spectrum also contains the combination bands characteristic of monosubstitution (at 1942, 1868, 1802, and 1741 cm ), and the out-of-plane C —H ring deformations for monosubstitution (757, 699, and 541 cm ). Note that the C—H stretching reflects the alternating methylene... 

The optically active alcohols (17,20-23) may then be brominated (PBrj) and used as alkylating agents for 4-hydroxybenzalde-hyde. The resulting 4-alkoxybenzaldehydes (25) were then condensed with a variety of mono-substituted aromatic amines (26 and 27) to give the two series of compounds shown in Scheme 3. 

This simple spectrum is often used as a wavelength calibration for infrared spectrometers. The principal feature of the spectrum is the mono-substituted aromatic bands, strong in the 13- to 15-/x region while weak in the 5- to 6-m region. Also of interest is the lack of other functionality. Polystyrene is often used as a cross-linking agent for polyesters and can be identified and quantitatively measured [ ]. 

The signals near 7 ppm are likely a result of aromatic protons. Notice that the combined integration of these signals is 5H, indicating a mono substituted aromatic ring ... 

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