Electronegativity natural, 127 tables

The Q and e values of VP are 0.088 and —1.62, respectively (125). This indicates resonance interaction of the double bond of the vinyl group with the electrons of the lactam nitrogen, whence the electronegative nature. With high e+ monomers such as maleic anhydride, VP forms alternating copolymers, much as expected (126). With other monomers between these Q and e extremes a wide variety of possibiHties exist. Table 14 Hsts reactivity ratios for important comonomers. 

The natural 7t-electronegativities of Table 3.11 are useful for estimating the bond polarities of pi bonds, as illustrated in the following example. 

Notice that this generalization follows naturally from the method of calculating oxida tion numbers outlined m Table 2 5 In a C—C bond one electron is assigned to one carbon the second electron to the other In a bond between carbon and some other ele ment none of the electrons m that bond are assigned to carbon when the element is more electronegative than carbon both are assigned to carbon when the element is less elec tronegative than carbon... 

Table 1-1 gives the values of the Mulliken electronegativity, the results of dividing these values by 2.69, and the values from The Nature of the Chemical Bond. (The factor 2.69 is the ratio of the sum of the first-row values to the sum of the third-row values.) The second reason for the failure to obtain a correlation is neglect of some of the structural features. Let us consider the factor 2.69 now. 

Table 3.9. A comparison of Pauling (xa

We can derive an approximate relationship between hybridization and natural electronegativity differences in the following manner. Even cursory inspection of the values in Table 3.8 suggests that AH increases as the electronegativity of the central atom decreases down a column of the periodic table. Equation (3.64) shows in turn that A,nb must diminish as central-atom electronegativity decreases. Relative to the average fractional p character of the bond + 1 hybrids,... 

Equation (3.79) leads to the natural 7t-electronegativity values displayed in Table 3.12. These values are compared with corresponding a-electronegativities of group 14-16 elements in Fig. 3.26. 

Table 3.12. Pi-type natural electronegativities xaw of group 14-16 elements...

From the polarities of the maximum-valency MH NBOs, one can infer the natural electronegativity Xm(N) of each transition metal M, following the procedure outlined in Section 3.2.5. For cases in which two or more inequivalent M—H bonds are present (e.g., RcH ), we employ the average value of cm2 (or of the bond ionicity z mh) to evaluate xm(N) from Eq. (3.60). Table 4.7 presents the natural electronegativity values for all three series of the d-block elements. 

Table 4.7. Natural electronegativity values Xm(N) ( Pauling units ) for d-block (group 3-11) elements of the first three transition series (Sanderson values19 xfs> for the first transition series are given in parentheses)...

From the pi-bond polarities in Table 4.11 we can readily infer natural pi electronegativity values for each metal atom, following the procedure outlined in Section 3.2.8. Numerical values of such pi electronegativities for the first three transition series are presented in Table 4.12. 

Table 4.12. Natural pi electronegativity values Pauling units") for the...

The effects of substituents in the -position to the radical center are mostly inductive in nature. Comparison of the RSE values for the ethyl radical (- 13.8 kj/mol) with those of the propyl, 2-hydroxyethyl, 2-fluoroethyl, and 2-chloroethyl radicals with RSE values of - 11.9, - 8.5, - 5.5, and - 6.7 kj/mol also indicates that electronegative substituents in the -position uniformly destabilize the radical center, the effect being larger for more electronegative substituents. Comparison of the RSE values of the 2-fluoro, 2,2-difluoro, and 2,2,2-trifluoroethyl radicals of - 5.5, + 3.0, and + 8.1 kj/mol also indicate that these effects can accumulate to yield overall destabilized radicals relative to the methyl radical. Even less favorable RSE values are found for positively charged substituents directly attached to the radical center such as - NH3+ (+ 18.3 kj/mol) or-SH2+ (+ 12.8 kj/mol) (Table 1). 

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