Steric parameter, Taft

It has been suggested that the discrepancies between the value of k ikK observed and that predicted on the basis of simple statistics may reflect the greater sensitivity of combination to steric factors. Beckhaus and Rtichardt164 reported a correlation between log(A )/ ,<.,) (after statistical correction) and Taft steric parameters for a scries of alkyl radicals. 

E Taft steric parameter. E reflects the effective volume... 

Taft steric parameter for para substituent on benzamide side chains. fTaft steric parameter for para substituent on benzyloxy side chains. gTaft steric parameter for para substituent on benzoyloxy side chains. hIndicator variable for polycyclic aromatics I = 1 if present, I = 0 if absent. 

Realistic prediction of the mutagenic activities of this class of mutagens requires a physicochemical evaluation of steric effects of substituents and the most widely utilised measures of such are Taft steric parameters, Es (Table 17).204,210... 

Analysis of the Hansch descriptors illustrates that increasing the lipophilicity property for this series of compounds will increase the bioactivity in a more dramatic fashion than increasing the Tafts steric parameter. Increasing the water accessible surface area (MOE descriptor) will increase the bioactivity of the compounds. But there is more than just adding lipophilicity and water accessible surface area to the molecules to increase binding affinity. A comparison of the substituents to the bioactivities illustrates that the bulkier X and Y groups increase bioactivity in conjunction with atomic partial charge distribution of the substituents. 

The C5+, and smeta values were experimentally determined, and the ASA, vdW and logP (o/w) were determined in MOE. [7t = lipophilicity parameter o+ = Hammett constant for ben-zylic cations Esmeta = Tafts steric parameter ASA = water accessible surface area vol = van der Waals volume logP (o/w) = log of the octanol/water partition coefficient.]... 

MacPhee, J. A., A. Panaye, and J.-E. Dubois, A critical examination of the Taft steric parameter-Es. Definition of a revised, broader and homogeneous scale. Extension to highly congested alkyl groups , Tetrahedron, 34, 3553-3562 (1978). 

TABLE 12.4 Selected Taft steric parameter values5... 

Predicting Hydrolysis Rate Difference Based on Substituents Sizes PROBLEM Based on Taft steric parameters, how much faster than ethyl acetate would you expect ethyl formate to hydrolyze ... 

Use a form of the Arrhenius equation (Equation 12.c) with Equation 12.17 to prove that the Taft steric parameter is indeed a function of activation energy ( a). 

Equation 12.21 correlates the Taft steric parameter of the R-group (Es) to the experimental activity of the molecule (log 1 //50). As with the previous section, the appropriate columns of activities and parameter values are created and entered into the LINEST function as... 

Taft steric parameter A Taft steric parameter describes the physical size of a substituent on a parent molecule. Taft parameters, denoted as Es, are often used in Hansch analyses to link lipophilicity changes to biological activity, tag A tag is a signal molecule that is attached to a bead to facilitate deconvolution in molecular libraries prepared by split... 

Taft steric parameters have been found to be useful in a number of investigations (see section 4.4.4). They also suffer from the disadvantage that they are determined by experiment. This has limited the number of values recorded in the literature. 

EC e.e. ELF EMEA EPC EPO Es Enzyme commission Enantiomeric excess Effluent load factor European medicines evaluation agency European Patent Convention European Patent Office Taft steric parameter... 

The activity of 1,1jl-trifluoro 3-mercapto substituted phenyl propan-2-ones was not simply correlated with MR alone, therefore, a combination of Hammett a constant, Taft steric parameter (Eg) and Hansch hydrophobic constant (x) was included in the regression analysis. "Equation 36" was found to be of the best fit for compounds substituted in the meta and para positions. 

To characterize the substituents (the X block) a set common substituent parameters were compiled from the literature. These parameters were as (Taft inductive parameter), trp (Hammett parameter for para substituents), F and R (Swain-Lupton dual substituent parameters), Es and Esc (Taft steric parameters), van der Waals radius, L, Bv B2, B3, (Verloop sterimol parameters), MR (molar refractivity), and n (Hansch lipophilicity parameter). Data are given in Refs. [1,19] and are not reproduced here. 

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