Constant Hammett

Intensities of the deformation vibration band near 1600 cm plotted for 2-aminothiazole and other 2-substituted thiazoles versus the Hammett constant give a linear relationship (123). 

C-nmr data have been recorded and assigned for a great number of hydantoin derivatives (24). As in the case of H-nmr, useful correlations between chemical shifts and electronic parameters have been found. For example, Hammett constants of substituents in the aromatic portion of the molecule correlate weU to chemical shifts of C-5 and C-a in 5-arylmethylenehydantoins (23). Comparison between C-nmr spectra of hydantoins and those of their conjugate bases has been used for the calculation of their piC values (12,25). N-nmr spectra of hydantoins and their thio analogues have been studied (26). The N -nmr chemical shifts show a linear correlation with the frequencies of the N—H stretching vibrations in the infrared spectra. 

The mechanism of the reaction is unknown. The stereospecificity observed with (E)- and (Z)-l-methyl-2-phenylethylene points to a one-step reaction. The very low Hammett constant, -0.43, determined with phenylethylenes substituted in the benzene ring, excludes polar intermediates. Yields of only a few percent are obtained in the reaction of aliphatic alkenes with (52). In the reaction of cyclohexene with (52), further amination of the aziridine to aminoaziridine (99) is observed. Instead of diphenylazirine, diphenylacetonitrile (100) is formed from diphenylacetylene by NH uptake from (52) and phenyl migration. 

C Hansch, RM Muir, T Fujita, PP Maloney, E Geiger, M Streich. The correlation of biological activity of plant growth regulators and chloromycetm derivatives with Hammett constants and partition coefficients. J Am Chem Soc 85 2817-2824, 1963. 

In the form of treatment developed by Taft and his colleagues since 195660-62, the Hammett constants are analyzed into inductive and resonance parameters, and the sliding scale is then provided by multiple regression on these. Equations 5 and 6 show the basic relationships. 

Oj and aR are respectively the inductive and resonance constants of Taft s analysis of ordinary composite Hammett constants (values obtained by Charton were used) and v is the steric substituent constant developed by Charton161,162. The intercept term, h, notionally corresponds to log k for H as an orfho-substituent, but is not found in practice always to agree closely with the observed value of log k for the parent system. 

Correlation of Relative Sweetness of 2-Substituted 5-Nltroanilines with Hammett Constant (tr) and Hydrophobicity (ir)... 

Deutsch and Hansch applied this principle to the sweet taste of the 2-substituted 5-nitroanilines. Using the data available (see Table VII), the calculated regression Eqs. 5-7 (using the method of least squares) optimally expressed the relationship between relative sweetness (RS), the Hammett constant, cr, and the hydrophobic-bonding constant, ir. 

The acid strengths of a series of phosphonic acid derivatives in a variety of solvents have also been used to estimate Hammett constants. In contrast to carboxylic acids, the phosphonic acids are stronger in ketonic solvents than in hydroxylic solvents, which may be attributed to the dissociation of phosphonic acids without the necessity to disrupt the dimeric nature of the acid (see Scheme 3). 

The strong electron-withdravhng effect of the CeFs group that is estimated to have a Hammett constant ap of 0.4 [16,17] and a Brown constant of 0.99 [18,19]. The... 

The Claisen-Schmidt condensation of 2 -hydroxyacetophenone and different chlorinated benzaldehydes over MgO has been investigated through kinetic and FTIR spectroscopic studies. The results indicate that the position of the chlorine atom on the aromatic ring of the benzaldehyde substantially affects the rate of this reaction. In particular, the rate increases in the following order p-chlorobenzaldehyde < m-chlorobenzaldehyde < o-chlorobenzaldehyde. The difference between the meta and para-substituted benzaldehyde can be attributed to electronic effects due to the difference in the Hammett constants for these two positions. Steric effects were found to be responsible for the higher rate observed with the o-chlorobenzaldehyde. 

Although this reaction occurs too rapidly for direct observation, the relative rate constants for pairs of phosphines were determined by standard kinetic competition techniques. The rate constant ratios for P(CeH4R)3 relative to PPh3 correlate well with the Hammett constant 3a, giving p = -0.70. 

Para carbon shieldings, however, clearly follow the pattern described by the canonical formulae. They may be correlated well with the total charge densities22 and with the Hammett constants. 

Since p-nitrosobenzoic acid has been shown to have a half-life of some 4 min in rat blood, this intermediate, once formed in the capillaries of the irradiated skin, may meet the requirement of sufficient stability to reach sensitive targets as the bone marrow while travelling through the blood141. The reactivity of p-nitrosobenzoic acid with thiols appears not to have been tested hitherto. From the known Hammett constant (ap = +0.4555) one may deduce that the compound will show a reactivity in between the reactivities of nitrosobenzene and p-nitrosoacetophenone. 

These data, e.g. predominant thiolytic cleavage of the semimercaptal at physiological GSH concentrations, is in line with the expected behavior in considering the positive Hammett constant of the sulfonamide substituent (op = +0.5855). It is to be expected that cells with lowered GSH content or impaired enzymic capacity to reduce GSSG will be... 

These data show that 4-nitrosodimethylaniline can deplete GSH in the liver by multiple reactions that are not exclusively related to the nitroso function, and it appears that the slow reactivity towards thiols correlates with the strongly negative Hammett constant... 

Upon reaction of 4-nitrosobiphenyl with thiols, its negative Hammett constant (op+ = —0.1855) is expected to facilitate formation of a sulfenamide cation that may delocalize its positive charge partly to C(3), C(2q and C(4/). Hence formation of aminophenols and acid-stable hemoglobin adducts would be conceivable. 

The first examples of this reaction (which was reviewed several times85), i.e. the addition of nitrosoarenes to 2,3-dimethylbutadiene to give 2-aryl-3,6-dihydro-2//-l,2-oxazines (equation 94), were reported in 194786. In general, the addition of nitroso compounds to 1,3-dienes to form dihydro-1,2-oxazines is only observed if the nitroso compound is activated by an electron-withdrawing group87. Kinetic studies of the reaction of cyclohexa-1,3-diene with para-substituted nitrosobenzenes (equation 95) show the accelerating effect of such groups (Hammett constant p = +2.57)88. 

The values of the Hammett constant , a, normally refer to the inductive electronic effects of the substituents in meta (crm) or para (crp) positions of aromatic rings. 

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