Electrical effects parameters for

C. Estimation of Electrical Effect Parameters for Dienyl and Polyenyl... 

It is often necessary to estimate values of electrical effect parameters for groups for which no measured values are available27. The equations available for the estimation of ai values for traws-vinylene (CH=CHZ) and vinylidene (CZ=CH2) groups are ... 

It is very often necessary to estimate values of electrical-effect parameters for groups for which no measured values are available. This is of particular importance with regard to substituents in which arsenic, antimony or bismuth is the central atom. It has long been known the electrical-effect parameters of substituents X whose structure can be written as MZ are a function of the electrical effect of the Z when M is held constant In later work it was shown that when Z is held constant and M is allowed to vary, the substituent constant is a function of the Allred-Rochow electronegativity of M, Xm and the number of Z groups, n. It has been shown that when both Z and M vary, values for all groups of the type X = MZ Z Z are given by an equation of the form ... 

Also examined were the chemical shifts of substituted nickel carbonyls, X—Ni(CO)3 . The ligands, X, had the form MZ3 where M is a group 15 element, usually phosphorus. It can be seen on inspection of the equations we have used to estimate electrical-effect parameters for Group 15 tricoordinate substituents that we can use these parameters as a measure of the electrical effect of the X groups in this data set. The best regression equation obtained is ... 

From quantum chemical calculations2 3. This method is most suitable for electrical effect parameters. 

The magnitude of p is in accord with a reaction at a ring C atom. Winkler and Winkler have also reported equilibrium and rate constants (sets CR7 and CR8, Table 9). We described above a modified Yukawa-Tsuno (MYT) equation (equation 6) with a taking the value for 3-substituted benzene derivatives and <750 for 4-substimted benzene derivatives, while for substituents in the meta position is 0. For this application the appropriate value of was unknown and all three pure electrical effect parameters were used for the para substituents thus the MYT equation used was equation 37 ... 

In order to include an group in a data set in which the substituents exhibit an steric effect it is necessary to know 0 so that the appropriate values of the delocalized electrical effect parameter, ctd and the steric parameter can be used. Values of 0 are usually unavailable. A method has been developed to circumvent this difficulty for chemical reactivities. The procedure is 1) A basis set, which contains only those members of the data set that show minimal dependence of their steric effect on conformation, is correlated with the LDS equation,... 

We have noted above that if steric effects are to be successfully separated from other substituent effects, it is vital that steric parameters show a minimal dependence on electrical effect parameters or transport parameters. Unger and Hansch 30) have reported that Es values of CH2X groups are significantly dependent on electrical effects. To resolve this question for the uef values we have carried out correlations of the u(CH2) Z values with the equation... 

A composite delocalized electrical-effect parameter of the type with rj equal to 2.04. It is derived from rate constants for the solvolysis of 4-substituted cumyl chlorides. 

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