Bond strengths, calculated

Blomberg, M. R. A., Siegbahn, P. E. M., 1998, Calculating Bond Strengths for Transition Metal Complexes in Computational Thermochemistry, Irikura, K. K., Frurip, D. J. (eds.), American Chemical Society Symposium Series 677, Washington, DC. 

Blomberg, M. R. A., Siegbahn, P. E. M., 1998, Calculating Bond Strengths for Transition Metal Complexes in... 

CN dimers (from -140.5 kcal/mol to -71.4 kcal/mol) and in the linear CP dimers (from -154.7 kcal/mol down to only -5.8 kcal/mol) as we go from C—C to C—X to X—X coupling. In the CN dimers, the reduction in bond strength is caused by an enormous increase in AE° repulsion (from 144.3 kcal/mol to 371.3 kcal/mol) which is counteracted but not compensated for by a sizable increase in AEoi (from -288.2 kcal/mol to -446.5 kcal/mol). In contrast, in the CP dimers the calculated bond strength decreases because of a weakening of the bonding orbital interactions AEoi (from -320.9 kcal/mol to -104.1 kcal/mol), especially those associated with the a bond (A CT) in spite of an opposite trend of the repulsion AE°, which actually decreases (from 161.5 kcal/mol to 91.0 kcal/ mol). 

In Fig. 4 another use of trends of calculated bond strengths is shown. In this case the bond strengths between the metal atoms and the methyl radical are compared to the bond strengths to the acetyl radical. For the acetyl radical, interaction between the metal and the lone pairs of the oxygen atom can be either attractive or repulsive, and an interesting question is how strong this interaction is. The metal-methyl bond... 

Validation of Calculated Bond Strengths in CH3OOH and CH3CH2OOH... 

Table 4. Experimental NMR shifts, calculated deshieldings and calculated bond strength siuns at Na for crystalline silicates and aluminosilicates from Xue and Stebbins (1993). Deshieldings calculated using average Na-0 distances are given in parenlheses and those directly calculated from Na-centered clusters are given in bold (from Tossell 1999b).

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