Hammett substituent parameters

The Hammett substituent parameter was used by Hansch as a concise measure of th electronic characteristics of the molecules. Hammett and others (such as Taft) showed the... 

The absolute rate constants for ene-addition of acetone to the substituted 1,1-diphenyl-silenes 19a-e at 23 °C (affording the silyl enol ethers 53 equation 46) correlate with Hammett substituent parameters, leading to p-values of +1.5 and +1.1 in hexane and acetonitrile solution, respectively41. Table 8 lists the absolute rate constants reported for the reactions in isooctane solution, along with k /k -, values calculated as the ratio of the rate constants for reaction of acetone and acctonc-rff,. In acetonitrile the kinetic isotope effects range in magnitude from k /k y = 3.1 (i.e. 1.21 per deuterium) for the least reactive member of the series (19b) to A hA D = 1.3 (i.e. 1.04 per deuterium) for the most reactive (19e)41. Arrhenius plots for the reactions of 19a and 19e with acetone in the two solvents are shown in Figure 9, and were analysed in terms of the mechanism of equation 46. 

A series of m- and -disubstituted anilides of thienoic acid and of 2-benzoylthiophenes, which have substituents at the m- and />-position of the benzoyl ring, have been prepared and their IR and NMR spectra obtained in 0.1 M chloroform-r/ solutions and DMSO-r4. The chemical shift values of each series were plotted against the Hammett substituent parameters to give good correlation. The slopes as well as the differences in chemical shift gave a set of meaningful values for the indexes of aromaticity <2002JHC1219>. 

Spectral Parameters and Hammett Substituent Parameters for Four-Substituted Benzenethiol Complexes PtHX(PPh3)a... 

This analysis allowed us to find a valuable logarithmic correlation between the experimental Hammett substituent parameter crp and the electrophilicity index given by ... 

Fig. 7.25 Plot of the logarithm of the rate constant for bromination of a substituted benzeneboronic acid relative to that of the unsubstituted acid, ogio(ki/kro) against the Hammett substituent parameter, ax-...

Determine the Hammett parameter pH for this equilibrium process using the Hammett substituent parameters given in table 7.10. 

The existence of a rough linear correlation between Vnse couplings and Hammett substituent parameters in 2-aryl-1,3,4-selenadiazoles has been suggested by Gierczyk et However, the range of the changes of these couplings is very small, 0.7 Hz only, i.e. from 56.7 to 57.4Hz, which makes this relationship doubtful. Much better correlations have been obtained for and Se chemical shifts. 

The kinetic trans effect of R in rra/u-[C o(dmgH)2(MeOH)R] varies in the order Me>Ph>S03 ->(Me0)2P0>MeCeH4S0a the rate of dissociation of MeOH correlating with the Hammett substituent parameter of R. A similar linear free-energy relationship exists for the dissociation of thiourea (tu) from fram-[Co(dmgH)2- L. Seibles and E. Deutsch, Inorg. Chem., 1977,16, 2273. 

Functionally substituted compounds bearing 192c were prepared from reactions of the corresponding substituted Cp Na, -Li, or -T1 reagents with [IrCl(CO)2(py)]. Ring-substituted compounds synthesized by this route include chloro, benzyl, pentabenzyl, acetyl, carbomethoxy. Me, benzoyl, trimethylsilyl, cyano, dimethylamino, tetraphenyl, dimethylaminoethyl, (tetramethyl)dimethylaminoethyl, methoxyethyl, and pentamethyl. The symmetrical and asymmetrical CO stretching frequencies as well as the C NMR chemical shifts of the carbonyl substituents were correlated with various Hammett substituent parameters. ... 

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