Is hydrogen electronegativity higher than Pauling’s value? New clues from the 13C and 29Si NMR chemical shifts of [AHF3] (A = C, Si) compounds

The study of the NMR chemical shift variations produced by monoatomic halido ligands bonded to NMR active central A atoms, in [AXn] compounds (Xn = combination of n halido ligands) is of wide interest. At this regard, we could previously demonstrate that the NMR chemical shift of a central 13C or 29Si atom, in simple [AX4] (A = C, Si; X4 = combination of four halides) tetrahalido derivatives, can be directly related to both ionic radii and Pauling’s electronegativities overall sums of the coordinated atomic ligands, Σ() and Σ(), respectively. [1,2] In this work, we extended this approach to halomethane and halosilane derivatives of the type [AHmXn] (A = C, Si; Xn = combination of n halido ligands; n+m = 4), by studying the 13C and 29Si NMR chemical shift variations of [AHmXn] compounds, as a function of Σ() and Σ(). In this way, new measurements for the hydrogen electronegativity, based on experimental molecular NMR data (), could be obtained. Remarkably, the hydrogen electronegativity obtained by these NMR data resulted higher than that reported by Pauling in its scale, but similar to that reported by Mulliken (= 2.75; =2.20; = 2.80). The importance of this new finding derives from the use of NMR data, based on molecular rather than atomic properties, in order to obtain a hydrogen electronegativity value similar to that calculated by Mulliken.