Boron hypercoordinate atoms

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... 

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