Nitrophenols structure

Phenol has different chemical properties from those of typical alcohols. Display the electrostatic potential map for phenol. Does this suggest that phenol is likely to be a stronger or weaker acid than any of the compounds discussed above Compare the electrostatic potential map for 4-nitrophenol to that for phenol. What effect does substitution by nitro have on acid strength Explain your result by considering charge delocalization in the conjugate base. Draw all reasonable Lewis structures for phenoxide anion and for 4-nitrophenoxide anion. Which is more delocalized Is this consistent with experimental pKa s ... 

In this solvent the reaction is catalyzed by small amounts of trimethyl-amine and especially pyridine (cf. 9). The same effect occurs in the reaction of iV -methylaniline with 2-iV -methylanilino-4,6-dichloro-s-triazine. In benzene solution, the amine hydrochloride is so insoluble that the reaction could be followed by recovery. of the salt. However, this precluded study mider Bitter and Zollinger s conditions of catalysis by strong mineral acids in the sense of Banks (acid-base pre-equilibrium in solution). Instead, a new catalytic effect was revealed when the influence of organic acids was tested. This was assumed to depend on the bifunctional character of these catalysts, which act as both a proton donor and an acceptor in the transition state. In striking agreement with this conclusion, a-pyridone is very reactive and o-nitrophenol is not. Furthermore, since neither y-pyridone nor -nitrophenol are active, the structure of the catalyst must meet the conformational requirements for a cyclic transition state. Probably a concerted process involving structure 10 in the rate-determining step... 

The importance of the proximity effect in cyclodextrin catalysis has been discussed on the basis of the structural data. Harata et al. 31,35> have determined the crystal structures of a-cyclodextrin complexes with m- and p-nitrophenols by the X-ray method. Upon the assumption that m- and p-nitrophenyl acetates form inclusion complexes in the same manner as the corresponding nitrophenols, they estimated the distances between the carbonyl carbon atoms of the acetates and the adjacent second-... 

Phenols (ArOH) are relatively acidic, and the presence of a substituent group on the aromatic ring has a large effect. The pKa of unsubstituted phenol, for example, is 9.89, while that of p-nitrophenol is 7.15, Draw resonance structures of the corresponding phenoxide anions and explain the data. 

Hammett (1937) observed that the value of the constant op for a nitro group as obtained from the acidity constant of 4-nitrobenzoic acid (crp = 0.78) was applicable, for example, to the rate of hydrolysis of ethyl 4-nitrobenzoate, but not to the acidity constants of 4-nitrophenol and 4-nitroanilinium ion. These two acidities were compatible only with significantly higher constants denoted by op (1.21 and 1.27, respectively). This was (correctly) interpreted as resulting from the donor-acceptor interaction represented by the mesomeric structures 7.7. 

Hydrogenation reactions, particularly for the manufacture of fine chemicals, prevail in the research of three-phase processes. Examples are hydrogenation of citral (selectivity > 80% [86-88]) and 2-butyne-l,4-diol (conversion > 80% and selectivity > 97% [89]). Eor Pt/ACE the yield to n-sorbitol in hydrogenation of D-glucose exceeded 99.5% [90]. Water denitrification via hydrogenation of nitrites and nitrates was extensively studied using fiber-based catalysts [91-95]. An attempt to use fiber-structured catalysts for wet air oxidation of organics (4-nitrophenol as a model compound) in water was successful. TOC removal up to 90% was achieved [96]. 

FIGURE 5.37 Chemical structure of a molecular probe with UV-Vis and fluorescence outputs for penicillin G amidase activity. The phenylacetamide group (red) is a substrate for PGA. The reporter units, 4-nitrophenol and 6-aminoquinoline, provide a visible signal and a fluorescence signal, respectively, upon release. (See the color version of this figure in Color Plates section.)... 

Cramer and co-workers (1967) have recently measured rate constants as well as equilibrium constants for the association of p-nitrophenol and a series of azo dyes with cydohexaamylose. The general structure of the dyes employed in this study is illustrated in Fig. 4. p-Nitrophenol and p-nitro-phenolate bind to cydohexaamylose with rate constants of about 108 M l sec-1, near the diffusion-controlled limit. Within the series of dyes, however, binding rates decrease by more than seven orders of magnitude as the steric bulk of the dye is increased. Equilibrium constants, on the other hand, are roughly independent of the steric nature of the substrate, indicating that association and dissociation rates are affected by similar... 

Also, Chin s dihydroxy-bridged dicobalt(III) complex 10 provides one of the largest rate enhancements ever observed for phosphodiester hydrolysis [36]. Reaction with the activated phosphodiester methyl(p-nitrophenyl)phosphate (MNPP) yields 11. A crystal structure is available for the analogous dimethylphosphate complex in which the Co ions are 2.9 A apart. At pH 7 and 45 °C 11 releases p-nitrophenolate with k = 0.1 s 1 which corresponds to a nearly 10I2-fold rate enhancement over spontaneous hydrolysis of the substrate. The product of the reaction is a methylphosphate-bridged complex. Based on the pH rate profile and on... 

In the ionization of the p-nitroanilinium ion, the free base is stabilized by delocalization of electrons involving the canonical structure 13. An analogous structure is not possible for the p-nitroanilinium ion. In the ionization of p-nitrophenol, analogous delocalization is possible in both phenol and phenate species, but is more marked in the ion. Thus, in both the aniline and the phenol system P-NO2 is effectively more electron-attracting than in the ionization of benzoic acid, where the reaction centre is incapable of a —R effect, and indeed shows a small +R effect (14). 

The anion of 4-nitrophenol is stabilized by resonance directly into the nitro group. The anion of 3-nitrophenol can t do this. Draw resonance structures to convince yourself of this. 

Fig. 28. Schematic drawing of the structure of 2,6-diphenyl-4-nitrophenol, which features O-H—77 interactions.144...

In the solid state, 2,6-diphenylphenol has a monomeric structure with an intramolecular O-H—tt interaction to one of the ortho-phenyl substituents.143 Interestingly, the 2,6-diphenyl-4-nitrophenol derivative has a dimeric structure in the solid state with intermolecular, as well as intramolecular, O-H—77 interactions between ortho-phenyl substituents.144 The latter compound represented the first example of bifurcated OH—77 bonding (Fig. 28). 

TT-Stacking interactions and solvation effects within the highly preorganized cleft of a bifunctional C-shaped host are believed to benefit the base-promoted conversion of 5-nitrobenzisoxazole to 2-cyano-5-nitrophenolate relative to the acetate-promoted reaction structural variation of the host has been explored. ... 

Ortho and para nitrophenols are more acidic than phenol. Draw the resonance structures of the corresponding phenoxlde ions. 

A good illustration of this concept is seen in a series of nitrophenols. The nitro group itself has to be drawn with charge separation to accommodate the electrons and our rules of bonding. However, resonance structures suggest that there is electron delocalization within the nitro group. 

Note that m-nitrophenol has pATa 8.4, and is a lot less acidic than o-nitrophenol or p-nitrophenol. We can draw no additional resonance structures here, and the nitro group cannot participate in further electron delocalization. The increased acidity compared with phenol can be ascribed to stabilization of resonance structures with the charge on a ring carbon through the nitro group s inductive effect. 

E Small molecular weight compounds of diverse structures p-Nitrophenol Disulfiram Ethanol Many haloalkenes and haloalkanes nitrosamines, benzenes... 

Hirshfeld (1964) pointed out that bond bending not only occurs in ring systems, but also results from steric repulsions between two atoms two bonds apart, referred to as 1-3 interactions. The effect is illustrated in Fig. 12.3. The atoms labeled A and A are displaced from the orbital axes, indicated by the broken lines, because of 1-3 repulsion. As a result, the bonds defined by the orbital axes are bent inwards relative to the internuclear vectors. When one of the substituents is a methyl group, as in methanol [Fig. 12.3(b)], the methyl-carbon-atom hybrid reorients such as to maximize overlap in the X—C bond. This results in noncolinearity of the X—C internuclear vector and the three-fold symmetry axis of the methyl group. Structural evidence for such bond bending in acyclic molecules is abundant. Similarly, in phenols such as p-nitrophenol (Hirshfeld... 

Other complexes described by the early workers include salicyl-aldehyde, o-nitrophenols, and acetylacetone as possible neutral ligands, HL, so that compounds of composition ML, HL or ML, HL were obtained. These were referred to as acid salts and illustrate the difficulty of deciding on a criterion for complex formation. Sfieakman (5)has reviewed the crystal structures of many acid salts of alkali metals in an investi-... 

Induction of DNA single-strand breakage in rat liver after in-vivo exposure to N-nitrosodiethanolamine was demonstrated in three studies and dose-dependent effects were shown. In one of these studies, the DNA strand-breaking potential of 7V-nitroso-diethanolamine was found to be abolished by inhibition of sulfotransferase by 2,6-dichloro-4-nitrophenol. Unscheduled DNA synthesis was not detected in rats or mice in an in-vivo/in-vitro hepatocyte DNA repair assay after treatment with 7V-nitrosodi-ethanolamine. A single study in mice exposed in vivo to 7V-nitrosodiethanolamine did not find any significant induction of structural or numerical chromosomal aberrations or micronuclei in bone-marrow cells. 

Section 6.2, the crystal forces are of magnitude comparable to those inducing complex formation. Thus a complex in the solid state can have a different structure from that in solution. The complex of p-nitrophenol 74 with hexakis(2,6-di-OMe)-a-cyclodextrin 75 illustrates this point, exhibiting strikingly different modes of entrance of the guest into the host cavity in these two states (Figure 3.4) [39]. Nevertheless, numerous solid state studies ofthe complexes... 

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