Protons aromatic ring

Benzene cannot be obtained directly from / ara-protonated aromatic rings in the polymer. However, j>ara-protonated rings can react with neighboring polymer chains to yield the same chain scission products that are formed by orf/zo-protonation. 

H, broad triplet, alkenyl proton, aromatic ring... 

For hydrocarbon studies, analyses can be made without prior assumptions, since the carbons not carrying protons can be excited directly, this of course not being the case for hydrogen (e.g., quaternary carbons in alkanes, substituted carbons in aromatic rings). 

FIGURE 13 10 More shielded (red) and less shielded (blue) protons in (a) [18]annulene and (b) [16]annulene The induced magnetic field associated with the aromatic ring current in [18]annulene shields the inside protons and deshields the out side protons The opposite occurs in [16]annulene which is antiaromatic... 

Many of the properties of phenols reflect the polarization implied by the resonance description The hydroxyl oxygen is less basic and the hydroxyl proton more acidic in phenols than m alcohols Electrophiles attack the aromatic ring of phenols much faster than they attack benzene indicating that the ring especially at the positions ortho and para to the hydroxyl group is relatively electron rich... 

The mechanism of these reactions involves the rapid and reversible addition of a proton to the aromatic ring, followed by 1,2-intramolecular methyl shifts (10) ... 

This is due to a resonance effect. Aniline is stabilized by sharing its nitrogen lone-pair electrons with the aromatic ring. In the anilinium ion, the resonance stabilization is dismpted by the proton bound to the lone pair. 

The symbols f and f correspond to total fraction of and hybridi2ed carbon, respectively, f represents the fraction of carbon in aromatic rings f , the fraction in carbonyls, b > 165 ppm the aromatic fraction that is protonated the aromatic fraction that is nonprotonated f, the phenoHc or phenohc ether carbon, 6 = 150-165 ppm f, the alkylated aromatic carbon, 6 = 135-150 ppm , the aromatic bridgehead carbon f represents the fraction of CH or CH2 aUphatic carbon f, the CH or nonprotonated aUphatic carbon and f, the aUphatic carbon bound to oxygen, b — 50-90 ppm. 

Z Arrangement was also ascribed to the isomer absorbing at higher field in the case of the ethyl compounds. CH and CH2 protons near the ring nitrogen are shielded by the aromatic ring in the Z compound. The protons at the ring carbon absorb at lower field (near 5.2 p.p.m.) in the Z compounds than in the E compounds (4.50-4.70 p.p.m.). The chemical shift of this proton may be used for E-Z discrimination in further substances. 

The Friedel-Crafts reaction is a very important method for introducing alkyl substituents on an aromatic ring. It involves generation of a carbocation or related electrophilic species. The most common method of generating these electrophiles involves reaction between an alkyl halide and a Lewis acid. The usual Friedel-Crafts catalyst for preparative work is AICI3, but other Lewis acids such as SbFj, TiC, SnCl4, and BF3 can also promote reaction. Alternative routes to alkylating ecies include protonation of alcohols and alkenes. 

Birch and others originally suggested that two electrons add to the aromatic ring affording a dicarbanion (34) which is subsequently protonated [Eq. (1)]. The preference for maximum separation of charge in dicarbanion... 

After completion of the reaction, the mixture is diluted with water, extracted with ether and the residue from the ether phase purified by chromatography and/or recrystallization. If the substrate contains aromatic protons, the reduction procedure is repeated in protic medium to back exchange deuteriums incorporated into the aromatic ring. 

Hydrogens that are directly attached to double bonds (vinylic protons) or to aromatic rings (aryl protons) are especially deshielded. 

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