Precision and Accuracy Plots

Figure 3.3 The Ea of benzonitrile, 1,2 dicyanoethylene, 1,2 dicyanobenzene, maleic anhydride, benzoquinone, s-tetracyanobenzene, fluoranil, chloranil, hexacyanobenzene, tetracyanoquinodimethane, tetracyanoethylene, and hexacyanobutadiene reported in 1975 [64] from reduction potentials and charge transfer absorption maximum versus the current best values. These are precision and accuracy plots. The slopes are determined with a fixed intercept of zero, so that the displacements are random uncertainties.

Figure 4.15 Electron affinities of charge transfer complex acceptors calculated from C2 = 2.9 versus the current best adiabatic electron affinities. This is a precision and accuracy plot. The zero intercept slope indicates that the same quantities are measured. The compounds are maleic anhydride, tetrachlorophthalic anhydride, benzoquinone, trinitro-flourenone, s-trinitrobenzene, chloranil, tetracyanoquinodimethane, and tetracyanoethylene in order of their electron affinities.

Figure 5.13 A precision and accuracy plot of the atomic electron affinities determined before 1967 versus the current best values. The deviations from the unit slope and zero intercept line result from random and systematic errors.

The experimental procedures for obtaining ECD and NIMS data have been described. Examples of the calculations are given for the various classes of molecules. For each group specific test molecules are provided. The aromatic hydrocarbons and aldehydes are Eql(l/lor 1/2) molecules, CS2 is a Eql(2/2) molecule, haloalkanes are DEC(l) molecules, and the halobenzenes and nitromethane are DEC(2) molecules that dissociate via a molecular ion. A graphical procedure for obtaining parameters from ECD data and the calibration of NIMS data using SF6 and nitrobenzene is presented. The use of multiple electron affinities of O2 to define negative-ion states from ECD data is illustrated. A method for the analysis of published NIMS spectra measured at two temperatures reveals the electron affinities of molecules when combined with substitution effects. We then explored the use of precision and accuracy plots and timelines for the evaluation of electron affinities. 

Figure 6.4 Precision and accuracy plot for direct capture magnetron data [2]. The values for the quinones are systematically lower than the others by 0.42 eV. The random uncertainty in the other values is 0.15 eV.

Figure 6.17 Precision and accuracy plot for reduction potential and charge transfer complex Ea for various quinones data published in 1975 [9, 78]. Systematic uncertainties can be identified as shown by parallel lines.

Figure 6.18 Precision and accuracy plot for Huckel Ea for aromatic hydrocarbons. The slope of the zero intercept line is less than 1, indicating systematic uncertainties [79].

The electron affinities of a series of substituted quinones have been calculated using the hybrid Hartree Fock/density functional B3LYP method with a 6-311G(3d,p) basis set. The precision and accuracy plot for the Ea obtained from... 

Figure 6.22 Precision and accuracy plot for rate constants determined by other techniques versus those determined by the ECD at room temperature [13, 91].

Figure 7.19 Precision and accuracy plot of the corrected values of the electron affinities of halogenated and methylated benzoquinones. These should be compared to the parallel lines in Figure 6.17. The compounds are listed in Table 6.3.

Random and systematic errors are characteristics of the method, not the values. Random errors can be determined by repeating the experiment. Systematic errors can only be determined by comparisons of values determined by different methods. Uncertainties can be estimated from precision and accuracy plots if it is assumed that there are only random errors. The Ea of the d and f block elements, electronegativities, and work functions of the elements will be evaluated in this chapter using this procedure. 

Figure 10.13 Precision and accuracy plots of the calibration data for charge transfer complex energy for the maximum absorbance. The charge transfer complex data were compiled in [71]. The data are given in Table 10.15.

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