Substituent effects monosubstituted benzenes

If, on the other hand, the encounter pair were an oriented structure, positional selectivity could be retained for a different reason and in a different quantitative sense. Thus, a monosubstituted benzene derivative in which the substituent was sufficiently powerfully activating would react with the electrophile to give three different encounter pairs two of these would more readily proceed to the substitution products than to the starting materials, whilst the third might more readily break up than go to products. In the limit the first two would be giving substitution at the encounter rate and, in the absence of steric effects, products in the statistical ratio whilst the third would not. If we consider particular cases, there is nothing in the rather inadequate data available to discourage the view that, for example, in the cases of toluene or phenol, which in sulphuric acid are nitrated at or near the encounter rate, the... 

First the five protons (integral) of the //NMR spectrum (Sfj = 7.50 - 7.94) in the chemical shift range appropriate for aromatics indicate a monosubstituted benzene ring with typical coupling constants 8.0 Hz for ortho protons, 1.5 Hz for meta protons.). The chemical shift values especially for the protons which are positioned ortho to the substituent Sn = 7.94) reflect a -M effect. Using the CH COLOC plot it can be established from the correlation signal hclS = 66.AI7.94 that it is a benzoyl group A. 

Retention volumes of monosubstituted benzenes, benzoic acid, phenols, and anilines have been measured in RPLC [76]. Buffered acetonitrile/water and tetrahydrofuran/water eluents were used with an octadecylsilica adsorbent. From the net retention volumes, a substituent interaction effect was calculated and described with the linear free energy relationship developed by Taft. The data was interpreted in terms of hydrogen bonding between the solutes and the eluent. 

Inductive and electric field effects of the substituents may overlap the o-mesomeric effects. However, the m and p shifts of monosubstituted benzenes generally follow the pattern discussed above. 

D.E. Ewing Org. Magn. Res. 12,499 (1979) and references cited therein this work compiles the substituent effects on carbon-13 shifts of 709 monosubstituted benzenes. 

The orientation and reactivity effects of substituents discussed for the substitution of monosubstituted benzenes also hold for disubstituted benzenes, except that the directing influences now come from two groups. Qualitatively, the effects of the two substituents are additive on the reactivity. We therefore would expect 4-nitromethylbenzene to be less reactive than methylbenzene... 

To define the effectiveness of the UV/H202 process on a wide range of priority pollutants in water, Sundstrom et al. (1989) conducted experiments in a recirculating flow reactor system with low-pressure UV lamps at 254 nm. The temperature of the solution was maintained at 25°C, and pH was maintained at 6.8 by a phosphate buffer. Molar ratio of peroxide to pollutant was varied during the experiments. As the molar ratio of peroxide to pollutant increased, the reaction rates increased. Three monosubstituted benzenes were selected to examine the effect of a single substituent group on the rate of reaction of benzene. The rates of reaction were of similar magnitude for benzene and monosubstituted benzenes (toluene, chlorobenzene, and phenol) at the ratio of 7 for peroxide to pollutant. 

Only data for substituents of the requisite symmetry are included in Fig. 19. These results adhere to the correlation with excellent precision. This observation confirms the general utility of the procedure. One caution is necessary. The p-value determined for non-catalytic bromina-tion of the monosubstituted compounds is — 12.1. The reaction parameter is decreased to — 8.7 for the bromination process with the polymethylbenzenes. The large variation in substituent effects is presumably the consequence of the greater overall reactivity of the alkylated benzenes. The dependence of p on the nature of the substrate is an important problem worthy of further attention. 

Figure 12. Molecular structures of some monosubstituted benzenes studied via TRPES in order to determine the quantitative accuracy of the extracted internal conversion rates. Three different electronic substituents were used, C=0, C=C, and C=C, leading to different state interactions. The effects of vibrational dynamics were investigated via the use of methyl group (floppier), as in a-MeSTY and ACP, or a ring structure (more rigid), as in IND, side-group additions. Both BZA and ACP have favorable Type (I) ionization correlations, whereas STY, IND, a-MeSTY, and ACT have unfavorable Type (II) ionization correlations.

Substituent Effects on Reactivity and Regioselectivity of Ar-SE Reactions of Monosubstituted Benzenes... 

A more detailed analysis of the stabilizing effect of donor substituents and the destabilizing effect of acceptor substituents (both are referred to as Subst in the following) on Wheland complexes E-QH5 -Subst explains, moreover, the regioselectivity of an Ar-SE attack on a monosubstituted benzene. Isomeric donor-containing Wheland complexes and acceptor-containing Wheland complexes have different stabilities. This follows from the uneven charge distributions in the Wheland complexes. 

A number of workers have reported the NMR spectra of mono-substituted phenyl groups and correlated the shifts vdth molecular parameters. It has been shown for organic compounds that the chemical shift of the para-carbon in monosubstituted benzenes is linearly related to the total TT-electron density at the para position in these compounds. Also the shift separation of the meta- and para-carbons appears to be linearly related to the rr-electron density on the para-carbon due to resonance interaction with the substituent 49, 156). Spiesecke and Schneider have reported a good linear relationship between the para-carbon chemical shift of monosubstituted benzenes and the Hammett, o-para constant, but no such relationship appears to exist for the other carbon chemical shifts, except between the chemical shift for the substituted carbon atom (corrected for magnetic anisotropy effects of the substituent) and the electronegativity of the substituent 210). 

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