Boronic hypercoordinated

GIAO-MP2/SCF/DFT calculated NMR hemical shift relationships in isostructural onium ions containing hypercoordinate boron, carbon, aluminum, and silicon atoms91... 

Subsequently, as more data accumulated on systems containing hypercoordinated boron and carbon atoms, it became evident that a roughly hnear relationship of slope of approximately 0.33 existed between the boron-11 and carbon-13 chemical shifts [a relationship to which both Eqs. (5.35) and (5.36) approximate]. This held for a wide range of isoelectronic pairs of boron and carbon compounds, as iUustrated in Figure 5.12 and Table 5.6, and in greater detail in Chapter 6 of the hrst edition of this book, written when the structures of carbocationic systems were stih to be resolved. Now that more structures have been determined, others can be calculated reliably, and disputes about them are few, we need to discuss only a few recent examples below, to illustrate what B- C NMR chemical shift relationships hold for... 

Using the GIAO-MP2 method (tzp/dz basis set), Rasul et aU " calculated the B NMR chemical shifts of hypercoordinate boron atoms in selected boron compounds and NMR chemical shifts of the corresponding isoelectronic and isostructural carbocations for systems not yet observed under long-lived superacidic conditions B NMR and NMR chemical shift values for the methonium ion CH5+ (5) and the corresponding neutral boron analog BHs (15) were shown to reproduce well the experimental values. Calculations were also performed for the six-coordinate carbocation (diprotonated methane, 18) seven-coordinate carbocation (triprotonated methane, 27) the... 

The correlation diagram (Fig. 5.13) indicates a good general correlation between the calculated NMR chemical shifts of hypercoordinate carbocations and the calculated B NMR chemical shifts of the corresponding isoelectronic and isostructural boron compounds.The correlation line corresponds roughly to that of Equation (5.36), though with slope 0.27 [c 0.33 for Eq. (5.36)]. 

FIGURE 10.6 (See color insert following page 202.) Optimized geometries of planar boron wheels containing a planar hypercoordinate group 14 element. 

Stabilizing these molecules. These results are in complete agreement with the conclusions drawn from the MO and B analysis, showing that extensive delocalization is a key factor for the stabilization of the boron wheels containing a hypercoordinate group 14 element. 

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