Steric constant Charton

Bowden-Young steric constant steric descriptors (O Charton steric constant) branching index Randic connectivity index - connectivity indices branching layer matrix layer matrices... 

Charton characteristic volume Charton steric constant -> steric descriptors... 

Both the b and k values were estimated by regression analysis from the Taft steric constant Es and the Charton steric constant in an iterative procedure using 96 substituents. The k values are equal to 1.0 for the second period elements, except for the fluorine atom (k = 0.8) k = 1.2,1.3, and 1.7 for the third, fourth, and fifth period elements, respectively. 

Charton steric constant vx (or Charton characteristic volnme) is defined as ... 

Values of the Charton steric constants are collected in Table S-2 for some atoms. 

The most popular substituent constants are electronic substituent constants, - Hansch-Fujita hydrophobic substituent constants and -> steric substituent constants such as - Taft steric constant, - Charton steric constant, -> substituent front strain, and - steric density parameter. 

Graph values of versus the Charton steric constant for the substituents C2H5-, H-, Me-, CH2Br-, CH2CI-, CH2I-, CH(Me)2-, Bu-, CCI3-, Ph-, CBr - and CEst. and values are found in tables in Appendix 3). 

Bowden-Young steric constant steric descriptors (0 Charton steric constant)... 

Charton steric constant Vx (or Charton characteristic volume) is defined as Vx = R -R = R -1.20... 

These can be broadly divided into those that apply to sections of the molecule and those that involve the whole molecule. The former include parameters such as van der Waals radii, Charton s steric constants and the Verloop steric parameters. The latter range from relative molecular mass (RMM) and molar volumes to surface area. They have all been used to correlate biological activity to structure with varying degrees of success. 

The regression coefficients a and b were estimated separately for each reaction series, and then additional Oj values (Charton inductive constants) were estimated and a set of recommended values also suggested. In general, steric and resonance effects in the acetic acid system can be considered negligible. Moreover, unlike the Taft inductive constants, those defined by Charton require only one experiment for their determination. 

The values of the van der Waals radii are taken from Charton. By using this equation, steric constants were also calculated for ortho-substituted and non-alkyl groups. 

The average of the minimum and maximum van der Waals radii as defined by Charton was correlated to the Taft steric constant (see above). 

Always based on the number of substituent carbon atoms in different positions, Charton proposed a general correlation equation with its steric constant v defined as V = f>o + hi a + 62 p + 63 Y + 4 na... 

Fujita, T. and Iwamura, H. (1983). Applications of Various Steric Constants to Quantitative Analysis of Structure-Activity Relationships. In Steric Effects in Drug Design (Topics in Current Chemistry, Vol. 114) (Charton, M. and Motoc, I., eds.), Springer-Verlag, Berlin (Germany), pp. 119-157. 

The use of the QSAR technique known as the Hansch Approach in the investigation of odor intensity and odorant physico-chemical properties has indicated that hydrophobic properties of homologous series of compounds, not steric or polar properties, are highly correlated to the level of odor intensity. This was shown to be the case for literature odor threshold and suprathreshold data determined at different laboratories using various media. The poor correlation between odor intensity and the steric properties of molecules (Taft Steric Constant) which had been reported earlier by this author (11) have been further verified by the use of Charton and Verloop Sterimol steric parameters. 

However, steric constants calculated via this method also differ distinctly from Charton steric parameters, as they probably contain significant contributions from the polar effect of R. 

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. 

Charton used statistical methods to investigate the contributions to Taft s s values of the size of the groups concerned and their polar effects. As a measure of group size he took the van der Waal s radius, rv, and he used o-, and crR as measures of inductive and mesomeric effects. Correlations of steric substituent constants were then carried out250 using the equation (for group x)... 

There is a considerable body of evidence both from polymerization studies and from gas-phase addition kinetics that radical reactivity is influenced by steric effects (see Section 3). Taft steric substituent constants Es are available for only a very few halogenoalkyl radicals (Charton, 1971), but it was found that log Or correlates well with E% for the few that are known (Ashton et al., 1975). 

While the development of the Taft parameter is similar to that of Hammett and Hansch, / )-val ucs are based on rate constants instead of equilibrium constants. The Taft parameter is a measure of changes in activation energy, not standard free energy. Of the Hammett, Hansch, and Taft parameters, the Taft parameter is utilized the least in QSAR studies. Other steric parameters have been developed over time, and like the Taft parameter, all have shortcomings. One alternative steric parameter was developed by Marvin Charton of Pratt Institute in New York. Charton s parameter is based on the van der Waal radius of a substituent.6 Another alternative steric model is the STERIMOL parameter set developed by Arie Verloop of Philips-Duphar in Holland.7 Unlike Taft and Charton, Verloop... 

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