Para-Nitroanisole

From the early days of the NMR spectroscopy it has been shown that solvent effects cannot be explained in terms of the dielectric constant of the solvent and do not correlate with the polarity of the medium. This could be shown in the example of para-nitroanisole [3] and 3,4,5-trimethoxybenzaldehyde (Table I) [4]. In para-nitroanisole it has been observed that solvent shifts of protons meta to the nitro... 

Likewise alkyl amines, 0-dealkylation (demethylation) of ethers are commonly observed for P-450 catalyzed oxidation [225, 242, 243]. Para-nitroanisole and 7-ethoxycoumarin are the typical substrates for the 0-dealkylation catalyzed by P-450 [242,... 

Dependence on probe location and orientation. Prom our discussion of the neat interface we now know that this region is very narrow, and the SHG peak spectrum will likely depend strongly on the solute location and orientation. This was proved by Steel and Walker who designed a series of surfactant solvatochromic probes they call molecular rulers.Each of these surfactant molecules consists of an anionic hydrophilic sulphate group (which is restricted to the aqueous phase), attached to a hydrophobic solvatochromic probe moiety by a variable length alkyl spacer. The probe is based on para-nitroanisole (PNA), whose bulk solution excitation maximum shifts monotonically with solvent polarity. When these surfactant molecules adsorb at the interface, the anionic end is in the aqueous phase, and the probe moiety resides at variable positions relative to the interface. 

According to Scheme 11, the isomeric ortho para) product ratios are established during the collapse of the radical pair in (64) (most probably at the positions of AN+- with the highest electron density). Furthermore, the absence of a measurable kinetic isotope effect in the decay of the deuterated analogue (C6D5OCH.v) in Table 3 is predicted from Scheme 11 since the proton loss occurs in a subsequent, rapid step (65). The absence of a deuterium kinetic isotope effect also indicates that the presence of pyridine in the triad in (63) does not lead to the nitroanisoles by an alternative... 

The ambiphilic reactivity of aromatic cation radicals, as described in Schemes 12 and 13, is particularly subtle in the charge-transfer nitration of toluene and anisole, which afford uniformly high (>95%) yields of only isomeric nitrotoluenes and nitroanisoles, respectively, without the admixture of other types of aromatic byproducts. Accordingly, let us consider how the variations in the isomeric (ortho meta para) product distributions with... 

Hz for the ortho, meta and/or para coupling constants of p-nitroanisole, two dinitrotoluenes and 2,4-dinitrochlorobenzene. Both reports indicate that other aromatic compounds investigated showed even less solvent dependence. 

It was recognized at an early stage that the fact that m-nitrophenyl phosphate and m-nitroanisole give a much cleaner and more efficient reaction than their ortho- and para-isomers, in itself, is not sufficient to conclude that the rate of reactions of the excited meta-compound with the nucleophile is higher. Such a more efficient photoreaction might also be explained by a longer lifetime of the excited metacompound, by a different intersystem crossing efficiency, etc. 

In certain cases, light promotes substitution reactions in aromatic compounds.34 One of the fascinating features of these reactions is an almost complete change in regioselectivity from that observed in the ground-state reactions. When the nitrocatechol ether 8.1 is irradiated in alkali or in methylamine, the nucleophilic substitution takes place meta to the nitro group. The nucleophilic substitution of p-nitroanisole 8.2, however, takes place para to the X-substituent. 

Nitrochlorobenzene-4-sulfonic acid can be prepared ako by sulfonation of o-nitrochlorobenzene (see Table III).This method,however,is inherently more costly and less reliable than the one given above (nitration of chlorobenzene-4-sulfonic acid), because it requires the isolation of o-nifrochlorobenzene and its separation from the para isomer. Nevertheless, the second method may be preferable technically under those circumstances where the demand for p-nitrochlorobenzene is so large that a use for the by-product ortho isomer is need. At the present time, the situation is reversed. The manufacture of o-nitroanisole uses so much o-nitrochloroben-zene that the accumulated para compound is partly used in making p-nitroaniline. 

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-... 

All of these effects are observed when comparing the rates of various electrophilic aromatic substitution reactions. Activating substituents increase the rate of reaction relative to benzene. The rate of reaction for the nitration of anisole, for example, was 9.7 x 10 times faster than nitration of benzene. The reaction of anisole with nitric and sulfuric acids, gave 44% of o-nitroanisole, 56% of p-nitroanisole and < 1% of m-nitro-anisole.2 9 contrasts with reactions involving deactivating substituents, where selectivity for the meta -product is usually very good. Nitration of nitrobenzene, for example, gave 1,3-dinitrobenzene in 94% yield, with only 6% of the ortho product and < 1% of the para product. ... 

One group of aryl halides that do undergo nucleophilic substitution readily consists of those that bear a nitro group ortho or para to the halogen. p-Chloronitrobenzene reacts with sodium methoxide at 85°C to give p-nitroanisole. The position of the nitro group on the ring is important. 

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