Is hydrogen electronegativity higher than Pauling’s value? New clues from the 13C and 29Si NMR chemical shifts of [CHF3] and [SiHF3] molecules

Michele Benedetti; Federica De Castro; Antonella Ciccarese; Francesco Paolo Fanizzi

doi:10.1515/pac-2019-0202

Publicly Available Published by De Gruyter August 17, 2019

Is hydrogen electronegativity higher than Pauling’s value? New clues from the ¹³C and ²⁹Si NMR chemical shifts of [CHF₃] and [SiHF₃] molecules

Michele Benedetti , Federica De Castro , Antonella Ciccarese and Francesco Paolo Fanizzi

From the journal Pure and Applied Chemistry

https://doi.org/10.1515/pac-2019-0202

Abstract

We previously demonstrated that the δ NMR chemical shift of central NMR active atoms (A), in simple halido [AX_n] (A=C, Si, Ge, Sn, Pb, Pt; X_n = combination of n halides, n = 4 or 6) derivatives, could be directly related to X radii overall sum, Σ(r_L). Further correlation have also been observed for tetrahedral [AX₄] (A=C, Si; X₄ = combination of four halides) compounds where the X Pauling electronegativities sum, Σ(χLPau), exceeds a specific value (≈12.4). In this work, we focused on these latter systems considering the H vs. X substitution. The analysis of the literature reported δ(¹³C) and δ(²⁹Si) NMR chemical shift for the mono hydrogenated derivatives and in particular for [CHF₃] and [SiHF₃], characterized by the lowest Σ(r_L) and the highest Σ(χLPau), suggests a revised value for the H electronegativity ranking with respect to Pauling’s.

Keywords: Eurasia 2018; halo-methane derivatives; halo-silane derivatives; hydrogen electronegativity; NMR spectroscopy

Introduction

The effect of mono-atomic L ligands, on the NMR chemical shift of the central A in [AL_n] (A=NMR active atom; L=generic monoatomic ligand) complexes, is of great interest [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]. At this regard, in the case of simple halido substituents Normal and Inverse Halogen Dependences (NHD and IHD, respectively), are generally observed. This corresponds in the NHD case, to a NMR chemical shift decrease of the central A, on increasing the steric hindrance of monoatomic ligands, vice-versa with IHD trends [3], [26], [27], [28], [29], [30], [31], [32], [33]. Theoretical approaches provided a definitive explanation for both trends, at a fundamental level [18], [19], [20], [21]. Nevertheless, in our previous work on halido derivatives of platinum and XIV group elements, we could relate both NHD and IHD trends, with the less fundamental but widely used chemico-physical parameters: r_L (ionic radius) and χLPau (Pauling’s electronegativity) of the monoatomic L ligand [34], [35], [36], [37], [38], [39]. We previously underlined, that this approach suggests the existence of electric ring currents, circulating around the L−A bonding axis, induced by applied magnetic fields. The advantage of this semi-empirical approach is that we can connect the NMR shielding ability of bonded monoatomic ligands to the basic properties of atoms generally used to describe molecular features [34], [35], [36], [37], [38], [39], [40], [41]. In other words, the NMR chemical shift of a central atom can be directly related to the NMR shielding ability of single atom ligands. In this way, we could also underline that, as expected, the electronegativity of single atom substituents plays a role in determining such a NMR shielding. Nevertheless, we interestingly found, in carbon and silicon tetrahalido derivatives, that this effect takes place only above a specific onset value (≈12.4) of the Pauling electronegativity overall sum of the single atom substituents, Σ(χLPau) [34].

Following our previous works on tetrahedral [AX₄] and [AH₄] (A=C, Si; X₄=combination of four halides) tetrahalido and tetrahydrido compounds (Fig. 1, Tables S1, S2) [34], [35], in this work we decided to extend our studies to the literature reported ¹³C and ²⁹Si NMR chemical shifts of partially hydrogenated [AH_mX_n] (A=C, Si; X_n=combination of n Cl and/or F halides; m+n=4; Σ(χLPau)≥12.4) compounds (Tables S3, S4) [32], [42]. Here we report new results offering interesting perspectives for the correlation of the NMR chemical shift of a central A atom, in [AH_mX_n] compounds, with both overall steric hindrance and electronegativity of the bonded atomic ligands. In analogy with a previous work by Robinson and Gillespie, we will continue to use the term ligand even for atoms bonded to a central carbon or silicon, notwithstanding their non-metallic character [43].

$Fig. 1: General structures of the considered [AX4] (A=C, Si; X4=combination of four halides) and [AHmXn] (A=C, Si; Xn=combination of n Cl and/or F halides; m+n=4) halomethane and halosilane derivatives, with atomic substituents and Pauling’s electronegativities overall sum, Σ(χLPau), ≥12.4.$\Sigma (\chi _L^{{\rm{Pau}}}),{\rm{ }} \ge 12.4.$ Generic halides, H, Cl, F, C and Si atoms are indicated in red, grey, green, blue, black and grey-blue, respectively.$

Fig. 1:

General structures of the considered [AX₄] (A=C, Si; X₄=combination of four halides) and [AH_mX_n] (A=C, Si; X_n=combination of n Cl and/or F halides; m+n=4) halomethane and halosilane derivatives, with atomic substituents and Pauling’s electronegativities overall sum, Σ(χLPau), ≥12.4. Generic halides, H, Cl, F, C and Si atoms are indicated in red, grey, green, blue, black and grey-blue, respectively.

Results and discussion

¹³C and ²⁹Si δ NMR chemical shifts as a function of the Σ(r_{_L} ) values, in tetrahedral [AL₄] (A=C, Si) systems with Σ(χLPau)≥12.4: the case of [AH_mX_n] compounds (X_n=combination of n halides; m+n=4)

The δ(¹³C) [32], [33], [44], [45], [46], [47] and δ(²⁹Si) [42], [48], [49], [50], [51] NMR chemical shifts for [AX₄] (A=C, Si; X₄=combination of four Cl and/or F halides, Tables S1, S2) and [AH_mX_n] (X_n=combination of n Cl and/or F halides; m+n=4; Σ(χLPau)≥12.4; Tables S3, S4) compounds are reported in graph vs. the overall sum of ionic radii of A bonded atomic L ligands, Σ(r_L), see Fig. 2a,b. The following ionic radii: r_F−=133 [52]; r_Cl−=181 [52]; r_Br−=196 [52]; r_I−=220 [52]; r_H−=208 pm [53], [54], [55] were used. All the considered compounds are characterized by high overall Pauling electronegativity sum, Σ(χLPau), for the A bonded atoms. Interestingly, these [AH_mX_n] hydrogenated compounds, with Σ(χLPau)≥12.4, show a specific behavior similar to that exhibited by the fully halogenated [AX₄] congeners, Fig. 2. The compounds characterized by high Pauling electronegativity overall sum of the C or Si bonded L atoms are generally located in the low Σ(r_L) region and exhibit lower than expected NMR chemical shifts, Fig. 2a,b [32], [42]. Indeed deviations from the linear correlation of δ vs. Σ(r_L), Equations 1 in the Experimental, are observed for both [AX₄] and [AH_mX_n] species. These deviations, quantified as ΔΣ(r_L) differences by Equations 2 and reported in Fig. 3a,b, have been already analyzed and discussed in a previous work, for the sole [AX₄] derivatives (Tables S1, S4) [34]. The ΔΣ(r_L) resulted linear dependent on the Pauling electronegativity overall sum for the single atomic substituents, Σ(χLPau), as indicated by Equations 3 and were found to be trigged by the specific minimum onset Σ(χLPau) value, equal to about 12.4, see Fig. 3a,b [34]. As discussed above, this effect can be expressed in term of electronegativity dependent apparent increase of the NMR effective atomic radii overall sum, ΔΣ(r_L), as shown by Equations 4. The Fig. 3a graph shows a trend of ΔΣ(r_L) vs. Σ(χLPau) values already observed for the fully halogenated [CX₄] and [SiX₄] species. In fact, these exhibit for ΔΣ(r_L) values a region where it is about zero or strongly reduced (below or in proximity of the onset Σ(χLPau) value, respectively) and a region where the ΔΣ(r_L) and Σ(χLPau) values are linearly related [34]. The mono-hydrogenated compounds in Fig. 3a graph appear to line up following the expected trend already observed for the fully halogenated species. Interestingly these H containing compounds, characterized by Σ(χLPau) higher than the onset value, appear linearly correlated with the ΔΣ(r_L) but shifted towards lower Σ(χLPau) on a line nearly parallel to that previously described for the fully halogenated species [34]. The shift from this latter line appears to be nearly double for [CH₂F₂] with respect to [CHF₃], [CHF₂Cl] and [CHFCl₂], Fig. 3a. Although limited to the restricted available data set, similar shifts are also observed for the silicon [SiHF₃] and [SiH₂F₂] derivatives, Fig. 3b.

$Fig. 2: (a, b) δ(13C) and δ(29Si) NMR chemical shifts vs. ionic radii overall sum of carbon and silicon bonded atomic ligands, Σ(rL), in tetrahedral [AX4] (A=C, Si; X4=combination of four halides) compounds. The partially hydrogenated [AHmXn] (Xn=combination of n Cl and/or F halides; m+n=4) compounds, with Pauling’s electronegativities overall sum of the atomic substituents, Σ(χLPau), ≥12.4$\Sigma (\chi _L^{{\rm{Pau}}}),{\rm{ }} \ge 12.4$ are indicated in yellow. The ΔΣ(rL) differences are shown in the graphs by horizontal blue double arrows. The shown red lines, interpolating the data points of the sole [ABrmIn] (m+n=4) compounds with Σ(χLPau)≪12.4,$\Sigma (\chi _L^{{\rm{Pau}}}) \ll 12.4,$ correspond to: ΔΣ(rL)=0.$

Fig. 2:

(a, b) δ(¹³C) and δ(²⁹Si) NMR chemical shifts vs. ionic radii overall sum of carbon and silicon bonded atomic ligands, Σ(r_L), in tetrahedral [AX₄] (A=C, Si; X₄=combination of four halides) compounds. The partially hydrogenated [AH_mX_n] (X_n=combination of n Cl and/or F halides; m+n=4) compounds, with Pauling’s electronegativities overall sum of the atomic substituents, Σ(χLPau), ≥12.4 are indicated in yellow. The ΔΣ(r_L) differences are shown in the graphs by horizontal blue double arrows. The shown red lines, interpolating the data points of the sole [ABr_mI_n] (m+n=4) compounds with Σ(χLPau)≪12.4, correspond to: ΔΣ(r_L)=0.

$Fig. 3: (a, b) ΔΣ(rL) differences vs. Σ(χLPau)$\Sigma (\chi _L^{{\rm{Pau}}})$ for [AX4] (A=C, Si; X4=combination of four Cl and/or F halides) and partially hydrogenated [AHmXn] (Xn=combination of n Cl and/or F halides; m+n=4) compounds with Σ(χLPau)≥12.4.$\Sigma (\chi _L^{{\rm{Pau}}}) \ge 12.4.$ In blue are indicated the straight lines interpolating the data points of the [AF4], [AClF3], [ACl2F2] and [ACl3F] compounds. As indicated, the previously calculated onset Σ(χLPau)$\Sigma (\chi _L^{{\rm{Pau}}})$ value corresponds to the intersection between last interpolating lines and the zero line [34]. The necessary corrections to be operated to the hydrogen electronegativity, calculated for the reference [CHF3] and [SiHF3] compounds (i.e. ΔχH−[CHF3]NMR$\Delta \chi _{H - [{\rm{CH}}{{\rm{F}}_3}]}^{{\rm{NMR}}}$ and ΔχH−[SiHF3]NMR$\Delta \chi _{H - [{\rm{SiH}}{{\rm{F}}_3}]}^{{\rm{NMR}}}$), are graphically shown by violet double arrows. By using, for the hydrogen atoms the corrected NMR effective electronegativity value (χHNMR=2.75),$(\chi _H^{{\rm{NMR}}} = 2.75),$ we can calculate the Σ(χLNMR).$\Sigma (\chi _L^{{\rm{NMR}}}).$ The ΔΣ(rL) vs. Σ(χLNMR)$\Sigma (\chi _L^{{\rm{NMR}}})$ values are reported in (c, d). It can be observed that in this case the behavior of the shown partially hydrogenated [AHmXn] compounds is identical to that of the sole halogenated [AX4] derivatives.$

Fig. 3:

(a, b) ΔΣ(r_L) differences vs. Σ(χLPau) for [AX₄] (A=C, Si; X₄=combination of four Cl and/or F halides) and partially hydrogenated [AH_mX_n] (X_n=combination of n Cl and/or F halides; m+n=4) compounds with Σ(χLPau)≥12.4. In blue are indicated the straight lines interpolating the data points of the [AF₄], [AClF₃], [ACl₂F₂] and [ACl₃F] compounds. As indicated, the previously calculated onset Σ(χLPau) value corresponds to the intersection between last interpolating lines and the zero line [34]. The necessary corrections to be operated to the hydrogen electronegativity, calculated for the reference [CHF₃] and [SiHF₃] compounds (i.e. ΔχH−[CHF3]NMR and ΔχH−[SiHF3]NMR), are graphically shown by violet double arrows. By using, for the hydrogen atoms the corrected NMR effective electronegativity value (χHNMR=2.75), we can calculate the Σ(χLNMR). The ΔΣ(r_L) vs. Σ(χLNMR) values are reported in (c, d). It can be observed that in this case the behavior of the shown partially hydrogenated [AH_mX_n] compounds is identical to that of the sole halogenated [AX₄] derivatives.

The observed positions of the data points for the considered carbon and silicon halo-hydrido derivatives reported in Fig. 3a,b, are characterized by the higher Σ(χLPau) values (Fig. 3a,b), suggesting that differently from halides, the NMR data derived electronegativity of the C and Si bonded hydrogens should be higher than that reported in the L. Pauling’s electronegativity scale [53], [54], [56].

Calculation of the NMR effective electronegativity value for the hydrogen atom, on the basis of the [CHF₃] and [SiHF₃] reference compounds

From the ¹³C and ²⁹Si NMR chemical shifts of [CHF₃], δ(¹³C)=+118.8 ppm [32], and [SiHF₃], δ(²⁹Si)=−77.8 ppm [42], reference compounds, reported in the graphs of Fig. 2a,b vs. Σ(r_L), it is possible to calculate the corresponding ΔΣ(r_L) values, see Experimental. As expected, these calculated values are the highest among those obtained for the [CH_mX_n] and [SiH_mX_n] hydrogenated compounds, characterized by Σ(χLPau)≥12.4, considered in this work (Tables S3, S4). This because the ΔΣ(r_L) are directly related to the Σ(χLPau). The ΔΣ(r_L) values vs. Σ(χLPau) for all considered [CH_mX_n] and [SiH_mX_n] compounds, including the fully halogenated are reported in the graphs of Fig. 3a,b. The data points of both [CHF₃] and [SiHF₃] reference compounds do not fall on the same straight lines interpolating the data points of the [CX₄] and [SiX₄] series of compounds (with Σ(χLPau)>12.4), respectively [34]. As described in the Experimental (Equations 5–7) we can easily calculate the corrections required for the Pauling’s hydrogen electronegativity, ΔχH−[AHF3]NMR, required to shift the data points of the [CHF₃] and [SiHF₃] reference compounds on the respective straight line interpolating the [CX₄] and [SiX₄] (X₄=combination of four F and/or Cl) derivatives with Σ(χLPau)>12.4,Fig. 3a,b. These corrections (ΔχH−[CHF3]NMR=0.52 and ΔχH−[SiHF3]NMR=0.59) for [CHF₃] and [SiHF₃] (Tables S3, S4), allow to calculate the following H electronegativity values: χH−[CHF3]NMR=2.72 and χH−[SiHF3]NMR=2.79 (Equations 6) required to align the data points of [CHF₃] and [SiHF₃] on the line interpolating the corresponding considered [CX₄] and [SiX₄] derivatives. Interestingly, it can be observed that the new obtained electronegativity values are very similar, producing an averaged χ¯H−[AHF3]NMR=2.75 value. It is noteworthy that the adoption of the χ¯H−[AHF3]NMR value in the calculation of the ligands’ electronegativity overall sum results in a realignment of the data reported in Fig. 3a,b for both considered series of [CH_mX_n] and [SiH_mX_n] compounds, see Fig. 3c,d. Indeed, this occurs also in the case of the dihydrogenated [CH₂X₂] and [SiH₂X₂] compounds. Therefore, taking into account the required H electronegativity correction, the behavior of hydrogenated compounds becomes similar to that observed for fully halogenated congeners. This suggests that, the hydrogen’s NMR effective electronegativity value could be simply indicated as: χHNMR=2.75, without any reference to particular compounds.

Several electronegativity scales, calculated by using many physical parameters, have been proposed over the years after the original Pauling’s concept definition [56]. Due to the importance of the Pauling’s electronegativity scale [54], the others are routinely normalized to the former, obtaining an overall ranking range defined by single dimensionless numbers between 0.78 and 4.00. A slight variability of the electronegativity values ascribed to the same element in the different scales is generally observed. Hydrogen should be highlighted among the atoms having the wider range of attributed electronegativities, with values from 2.0 to 2.8 (χHLang−Smith=2.00; χHAllred−Rochov≈χHPauling=2.20;χHSanderson= 2.31; χHMulliken= 2.80) [56]. Interestingly, our calculated χHNMR value is higher than the hydrogen electronegativity reported in the Pauling’s scale, but similar to the normalized value reported by Mulliken, which is the highest for H. It should be noted, that Pauling’s and Mulliken’s electronegativities of halides are both similarly NMR effective in the studied systems, but this does not occur for Hydrogen, where a correspondence is found only with the value reported by Mulliken. Noteworthy, it appears clear from the data of the present paper, that the H electronegativity should be better located above that of both C and Si (according to Mulliken [57] and the absolute electronegativity scale calculated with the Pearson–Parr approach [58], [59]) and not between them (according to Pauling). This buttresses our approximation of considering hydrogens as C and Si bonded hydrido ligands with respect to the considered central atoms. As stated by L. Pauling, the electronegativity can be defined as “the power of an atom in a molecule to attract electrons to itself” [53], [54]. This definition often loses the link to a molecule related property in the basic statement defining other scales (including Mulliken) [57]. It should be noted that the present approach allows a realignment of Hydrogen electronegativity to that of the Mulliken scale (based on atomic data) by using exclusively experimental NMR data of molecular compounds.

Conclusion

In this work, we have extended to the considered [AH_mX_n] (A=C, Si; X_n=combination of n Cl and/or F halides; m+n=4, with Σ(χLPau)≥12.4) halo-hydrido derivatives the NMR chemical shifts analysis of the central atom (i.e. ¹³C, ²⁹Si) as a function of the bonded ligands and their Pauling electronegativities (χLPau), already performed for simple halido [AX₄] compounds [34]. The observed deviation in the NMR chemical shifts from the previously reported Σ(χLPau) general dependence [34], suggests a correction for the H electronegativity to a value (χHNMR=2.75) higher than that reported by L. Pauling (χHPau=2.20) [53], [54]. The calculated χHNMR value falls at the higher extreme of the range (2–2.8) covered by the normalized H’s electronegativity values in the most common scales and is almost perfectly corresponding to that reported by Mulliken (χHMulliken=2.80) [57]. Consistently, in a previous work, by analyzing the ¹³C, ²⁹Si, ⁷³Ge, ¹¹⁹Sn, and ²⁰⁷Pb NMR chemical shifts of [AH₄] (A=C, Si, Ge, Sn and Pb) compounds we found that the A bonded hydrogens show a very low radius variability (≈1%) suggesting a constant oxidation state of the bonded hydrogen atoms along the series [39]. This indirectly confirms the present findings, suggesting that the hydrogen electronegativity should be considered higher than that of carbon. Interestingly, the present approach allows this specific electronegativity value realignment exclusively using molecules related experimental NMR data, rather than single atoms properties. Therefore in a way we were able to obtain H electronegativity value close to that obtained by Mulliken (based on atomic data) by using molecular compounds features (Pauling’s like approach).

Experimental section

The here adopted ionic radii are: r_F−=133 [52]; r_Cl−=181 [52]; r_Br−=196 [52]; r_I−=220 [52] and r_H−=208 pm [53], [54], [55], instead the used Pauling’s electronegativity values are: χFPau=3.98; χClPau=3.16;χBrPau= 2.96; χIPau= 2.66; χH Pau=2.20.

Influence of steric hindrance and electronegativity of atomic substituents on the ¹³C and ²⁹Si NMR chemical shifts of [AH_mX_n] (A=C, Si; X_n=combination of n Cl and/or F halides; m+n=4) compounds

The ¹³C and ²⁹Si NMR chemical-shift of [AX₄] (X₄=combination of four halides) compounds are reported in Tables S1, S2 together with the overall sum of halides ionic radii, Σ(r_L). Instead in Tables S3, S4 are reported the ¹³C and ²⁹Si NMR chemical shifts of the considered [AH_mX_n] compounds whose Σ(χLPau)≥12.4, together with the Σ(r_L) values. Last NMR data are plotted in the graphs of Fig. 2a,b vs. Σ(r_L). In these graphs the red straight lines of Fig. 2a,b are obtained by interpolation of the data points of the subgroup of [ABr_mI_n] (A=C, Si; m+n=4) compounds, characterized by a Σ(χLPau)≪12.4, as previously shown [34]. These straight lines correspond to the following Equations:

(1A)δ(13C)=iC+sC⋅Σ(rL)

where i_C=2126.5 ppm; s_C=–2.7488 ppm/pm.

(1B)δ(29Si)=iSi+sSi⋅Σ(rL)

where i_Si=2031 ppm; s_Si=−2.703 ppm/pm.

We can calculate the horizontal distance, indicated as ΔΣ(r_L) in the graphs of Fig. 2a,b (blue double arrows), between a given data point and the corresponding straight line, as follows:

(2A)ΔΣ(rL)=δ(13C)−iCsC−Σ(rL)

(2B)ΔΣ(rL)=δ(29Si)−iSisSi−Σ(rL)

We previously shown that when Σ(χLPau)>12.4, for the two groups of cabon ([CF₄], [CF₃Cl], [CF₂Cl₂], [CFCl₃]) and silicon ([SiF₄], [SiF₃Cl], [SiF₂Cl₂], [SiFCl₃]) tetrahalido coordination compounds there exist linear correlations (R²≈0.999) between ΔΣ(r_L) and Σ(χLPau) as described by following equations [34]:

(3A)ΔΣ(rL)=jC+tC⋅Σ(χLPau)

where j_C=−731 pm; t_C=+58.3 pm.

(3B)ΔΣ(rL)=jSi+tSi⋅Σ(χLPau)

where j_Si=−892 pm; t_Si=+72.3 pm.

Last straight lines are represented in the graphs of Fig. 3a,b, by blue skew lines crossing the zero line in proximity of the averaged onset electronegativity value corresponding to: Σ(χLPau)≈12.4 [34].

Following Equations deriving from Equations 1 directly relate the δ(¹³C) and δ(²⁹Si) NMR chemical shifts to the Σ(r_L) and ΔΣ(r_L) values in the Σ(χLPau)>12.4 range, given that when Σ(χLPau)<12.4 it results ΔΣ(r_L)≈0 [34]:

(4A)δ(13C)=iC+sC⋅[Σ(rL)+ΔΣ(rL)]

(4B)δ(29Si)=iSi+sSi⋅[Σ(rL)+ΔΣ(rL)]

It is noteworthy that none of the considered hydrogenated [AH_mX_n] derivatives, showing a Σ(χLPau)≥12.4, falls on the straight lines calculated by Equations 3, evidenced in blue, in Fig. 3a,b.

In the case of [CHF₃] and [SiHF₃] compounds, the following Equations give the NMR effective electronegativity sum, Σ(χH−[AHF3]NMR), of C and Si bonded atoms:

(5A)Σ(χH−[CHF3]NMR)=[ΔΣ(rL)−jC]tC=14.655

(5B)Σ(χH−[SiHF3]NMR)=[ΔΣ(rL)−jSi]tSi=14.733

By subtracting the contribution of the Pauling’s fluorine atoms electronegativity (χFPau=3.98) from the last calculated sums we can obtain the NMR effective electronegativity of the single bonded hydrogen atom in the considered [CHF₃] and [SiHF₃] compounds:

(6A)χH−[CHF3]NMR=Σ(χL−[CHF3]NMR)−3χF Pau=2.715

(6B)χH−[SiHF3]NMR=Σ(χL−[SiHF3]NMR)−3χF Pau=2.793

The differences between the NMR effective and the Pauling’s electronegativities overall sums are as follows:

(7A)ΔχH−[CHF3]NMR=Σ(χL−[CHF3]NMR)−Σ(χL−[CHF3]Pau)=0.52

(7B)ΔχH−[SiHF3]NMR=Σ(χL−[SiHF3]NMR)−Σ(χL−[SiHF3]Pau)=0.59

These are graphically shown by horizontal violet double arrows in the graphs of Fig. 3a,b, for both reference [CHF₃] and [SiHF₃] compounds. Because the hydrogen electronegativity value is expected to be constant and independent from molecular environment, we can indicate the averaged NMR effective electronegativity of hydrogen (χ¯H−[AHF3] NMR=2.75) simply as: χHNMR and use this value as NMR effective electronegativity of the bonded hydrogen atom.

Article note

A collection of invited papers based on presentations at the 15^th Eurasia Conference on Chemical Sciences (EuAsC₂S-15) held at Sapienza University of Rome, Italy, 5–8 September 2018.

Acknowledgments

The University of Salento (Italy), the PON 254/Ric. Potenziamento del “CENTRO RICERCHE PER LA SALUTE DELL’UOMO E DELL’AMBIENTE” Cod. PONa3_00334, and the Consorzio Interuniversitario di Ricerca in Chimica dei Metalli nei Sistemi Biologici (CIRCMSB), Bari (Italy), are acknowledged for financial support.

Authors Contribution M.B. and F.P.F. designed research; M.B., A.C. and F.D.C performed research; M.B. performed calculations; M.B. and F.P.F. analyzed data; M.B. and F.P.F. wrote the paper; M.B. and F.P.F. active discussion and paper revision.

References

[1] H. Genther. NMR Spectroscopy, 2^nd ed., Wiley, New York (1995).Search in Google Scholar

[2] H. Marsmann. ²⁹Si NMR Spectroscopic Results, Oxygen-17 and Silicon-29-NMR Basic Principles and Progress, pp. 65–235, Springer, Berlin, Heidelberg 17, (1981).10.1007/978-3-642-87762-9_2Search in Google Scholar

[3] P. S. Pregosin. Transition Metal Magnetic Resonance, Elsevier, Amsterdam (1991).Search in Google Scholar

[4] M. R. Burger, J. Kramer, H. Chermette, K. R. Koch. Magn. Reson. Chem.48, S38 (2010).10.1002/mrc.2607Search in Google Scholar

[5] B. M. Still, P. G. Anil Kumar, J. R. Aldrich-Wright, W. S. Price. Chem. Soc. Rev.36, 665 (2007).10.1039/B606190GSearch in Google Scholar

[6] S. Fukawa, M. Hada, R. Fukuda, S. Tanaka, H. Nakatsuji. J. Comput. Chem.22, 528 (2001).10.1002/1096-987X(20010415)22:5<528::AID-JCC1024>3.0.CO;2-9Search in Google Scholar

[7] C. Corminboeuf, T. Heine, J. Weber. Chem. Phys. Lett.357, 1 (2002).10.1016/S0009-2614(02)00372-XSearch in Google Scholar

[8] C. S. Weinert. ISRN Spectroscopy2012, 1 (2012).10.5402/2012/718050Search in Google Scholar

[9] J. C. Davis, M. Bühl, K. R. Koch. J. Chem. Theory Comput.8, 1344 (2012).10.1021/ct300105qSearch in Google Scholar

[10] B. E. G. Lucier, K. E. Johnston, W. Xu, J. C. Hanson, S. D. Senanayake, S. M. Yao, W. Bourassa, M. Srebro, J. Autschbach, R. W. Schurko. J. Am. Chem. Soc.136, 1333 (2014).10.1021/ja4076277Search in Google Scholar

[11] A. F. Maldonado, C. A. Gimenez, G. A. Aucar. Chem. Phys.395, 75 (2012).10.1016/j.chemphys.2011.08.020Search in Google Scholar

[12] A. F. Maldonado, G. A. Aucar. J. Phys. Chem. A118, 7863 (2014).10.1021/jp502543mSearch in Google Scholar

[13] Y. Takeuchi, K. Tanaka, T. Harazono, S. Yoshimura. Bull. Chem. Soc. Jpn. 63, 708 (1990).10.1246/bcsj.63.708Search in Google Scholar

[14] R. Vivas-Reyes, F. D. Proft, M. Biesemans, R. Willem, P. Geerlings. J. Phys. Chem. A106, 2753 (2002).10.1021/jp0145917Search in Google Scholar

[15] P. Avalle, R. K. Harris, P. B. Karadakov, P. J. Wilson. Phys. Chem. Chem. Phys.4, 5925 (2002).10.1039/b208435jSearch in Google Scholar

[16] A. Bagno, G. Casella, G. Saielli. J. Chem. Theory Comput.2, 37 (2006).10.1021/ct050173kSearch in Google Scholar

[17] E. Malkin, S. Komorovsky, M. Repisky, T. B. Demissie, K. Ruud. J. Phys. Chem. Lett.4, 459 (2013).10.1021/jz302146mSearch in Google Scholar

[18] J. Autschbach, T. Ziegler. Relativistic Computation of NMR Shielding and Spin-Spin Constants-Encyclopedia of Nuclear Magnetic Resonance, pp. 306, Wiley, Chichester, (2002).10.1002/chin.200332285Search in Google Scholar

[19] H. Nakatsuji, H. Takashima, M. Hada. Chem. Phys. Lett.233, 95 (1995).10.1016/0009-2614(94)01409-OSearch in Google Scholar

[20] H. Nakatsuji, T. Nakajima, M. Hada, H. Takashima, S. Tanaka. Chem. Phys. Lett.247, 418 (1995).10.1016/S0009-2614(95)01266-4Search in Google Scholar

[21] H. Kaneko, M. Hada, T. Nakajima, H. Nakatsuji. Chem. Phys. Lett.261, 1 (1996).10.1016/0009-2614(96)00906-2Search in Google Scholar

[22] T. N. Mitchell. J. Organomet. Chem. 255, 279 (1983).10.1016/S0022-328X(00)99319-7Search in Google Scholar

[23] P. J. Watkinson, K. M. Mackay. J. Organomet. Chem.275, 39 (1984).10.1016/0022-328X(84)80575-6Search in Google Scholar

[24] J. D. Kennedy, W. Mcfarlane, G. S. Pyne. J. Chem. Soc., Dalton Trans.23, 2332 (1977).10.1039/dt9770002332Search in Google Scholar

[25] J. A. Tossell. Nuclear Magnetic Shieldings and Molecular Structure, Kluwer Academic Publishers, Dordrecht (1993).10.1007/978-94-011-1652-7Search in Google Scholar

[26] R. G. Kidd. Annu. Rep. NMR Spectrosc.10A, 1 (1980).Search in Google Scholar

[27] R. G. Kidd. Annu. Rep. NMR Spectrosc.23, 85 (1991).10.1016/S0066-4103(08)60276-8Search in Google Scholar

[28] M. Benedetti, P. Papadia, C. R. Girelli, F. De Castro, F. Capitelli, F. P. Fanizzi. Inorg. Chim. Acta428, 8 (2015).10.1016/j.ica.2015.01.003Search in Google Scholar

[29] H. O. Kalinowski, S. Berger, S. Braun. ¹³C-NMR-Spektroskopie, Thieme, Stuttgart (1984).Search in Google Scholar

[30] M. Kaupp, O. L. Malkina, V. G. Malkin, P. Pyykkö. Chem. Eur. J.4, 118 (1998).10.1002/(SICI)1521-3765(199801)4:1<118::AID-CHEM118>3.0.CO;2-6Search in Google Scholar

[31] A. A. Cheremisin, P. V. Schastnev. J. Magn. Res.40, 459 (1980).10.1016/0022-2364(80)90003-7Search in Google Scholar

[32] R. Gollakota, J. Somayajulu, R. Kennedy, T. M. Vickrey, B. J. Zwolinski. J. Magn. Reson.33, 559 (1969).10.1016/0022-2364(79)90167-7Search in Google Scholar

[33] R. A. De Marco, W. B. Fox, W. B. Moniz, S. A. Sojka. J. Magn. Reson.18, 522 (1975).10.1016/0022-2364(75)90107-9Search in Google Scholar

[34] M. Benedetti, F. De Castro, F. P. Fanizzi. Chem. Eur. J.23, 16877 (2017).10.1002/chem.201703934Search in Google Scholar

[35] M. Benedetti, F. De Castro, A. Ciccarese, F. P. Fanizzi. Dalton Trans.46, 14094 (2017).10.1039/C7DT03348FSearch in Google Scholar

[36] M. Benedetti, F. De Castro, E. Lamacchia, C. Pacifico, G. Natile, F. P. Fanizzi. Dalton Trans. 46, 15819 (2017).10.1039/C7DT03644BSearch in Google Scholar

[37] M. Benedetti, F. De Castro, D. Antonucci, P. Papadia, F. P. Fanizzi. Dalton Trans.44, 15377 (2015).10.1039/C5DT02285ASearch in Google Scholar

[38] M. Benedetti, F. De Castro, F. P. Fanizzi. Eur. J. Inorg. Chem.2016, 3957 (2016).10.1002/ejic.201600573Search in Google Scholar

[39] M. Benedetti, F. De Castro, F. P. Fanizzi. Dalton Trans.46, 2855 (2017).10.1039/C7DT00307BSearch in Google Scholar PubMed

[40] M. Benedetti, C. R. Girelli, D. Antonucci, F. P. Fanizzi. J. Organomet. Chem.771, 40 (2014).10.1016/j.jorganchem.2014.05.014Search in Google Scholar

[41] M. Benedetti, D. Antonucci, C. R. Girelli, F. P. Fanizzi. Eur. J. Inorg. Chem.2015, 2308 (2015).10.1002/ejic.201500103Search in Google Scholar

[42] U. Niemann, H. C. Marsmann. Z. Naturforsch. 30b, 202 (1975).10.1515/znb-1975-3-413Search in Google Scholar

[43] E. A. Robinson, R. J. Gillespie. Inorg. Chem.43, 2318 (2004).10.1021/ic030290vSearch in Google Scholar PubMed

[44] W. M. Litchman, D. M. Grant. J. Am. Chem. Soc.90, 1400 (1968).10.1021/ja01008a005Search in Google Scholar

[45] P. C. Lauterbur. Ann. NY Acad. Sci.70, 841 (1958).10.1111/j.1749-6632.1958.tb35435.xSearch in Google Scholar

[46] O. W. Howarth, R. J. Lynch. Mol. Phys.15, 431 (1968).10.1080/00268976800101301Search in Google Scholar

[47] G. R. Fulmer. Organometallics29, 2176 (2010).10.1021/om100106eSearch in Google Scholar

[48] R. B. Johannesen, F. E. Brinkman, T. D. Coyle. J. Phys. Chem. 72, 660 (1968).10.1021/j100848a047Search in Google Scholar

[49] F. Klanberg, E. L. Muetterties. Inorg. Chem. 7, 155 (1968).10.1021/ic50059a032Search in Google Scholar

[50] T. Heine. J. Phys. Chem. A.105, 620 (2001).10.1021/jp002495kSearch in Google Scholar

[51] G. A. Olah’, L. D. Field. Organometallics1, 1485 (1982).10.1021/om00071a016Search in Google Scholar

[52] R. D. Shannon. Acta Crystallogr. Sect.A32, 751 (1976).10.1107/S0567739476001551Search in Google Scholar

[53] L. Pauling. J. Am. Chem. Soc.54, 3570 (1932).10.1021/ja01348a011Search in Google Scholar

[54] L. Pauling. The Nature of the Chemical Bond 3^rd, 13^th Printing 1995 ed., Cornell University Press, Ithaca, New York (1960).Search in Google Scholar

[55] D. F. C. Morris, G. L. Reed. J. Inorg. Nucl. Chem.27, 1715 (1965).10.1016/0022-1902(65)80037-9Search in Google Scholar

[56] M. R. Leach. Found. Chem.15, 13 (2013).10.1007/s10698-012-9151-3Search in Google Scholar

[57] R. S. Mulliken. J. Chem. Phys.2, 782 (1934).10.1063/1.1749394Search in Google Scholar

[58] R. G. Parr, R. G. Pearson. JACS105, 7512 (1983).10.1021/ja00364a005Search in Google Scholar

[59] R. G. Pearson. Inorg. Chem.27, 734 (1988).10.1021/ic00277a030Search in Google Scholar

Supplementary Material

The online version of this article offers supplementary material (https://doi.org/10.1515/pac-2019-0202).

Published Online: 2019-08-17

Published in Print: 2019-10-25

©2019 IUPAC & De Gruyter. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. For more information, please visit: http://creativecommons.org/licenses/by-nc-nd/4.0/

Is hydrogen electronegativity higher than Pauling’s value? New clues from the ¹³C and ²⁹Si NMR chemical shifts of [CHF₃] and [SiHF₃] molecules

Abstract

Introduction

Results and discussion

¹³C and ²⁹Si δ NMR chemical shifts as a function of the Σ(r_{_L} ) values, in tetrahedral [AL₄] (A=C, Si) systems with Σ(χLPau)≥12.4: the case of [AH_mX_n] compounds (X_n=combination of n halides; m+n=4)

Calculation of the NMR effective electronegativity value for the hydrogen atom, on the basis of the [CHF₃] and [SiHF₃] reference compounds

Conclusion

Experimental section

Influence of steric hindrance and electronegativity of atomic substituents on the ¹³C and ²⁹Si NMR chemical shifts of [AH_mX_n] (A=C, Si; X_n=combination of n Cl and/or F halides; m+n=4) compounds

Article note

Acknowledgments

References

Supplementary Material

Journal and Issue

Articles in the same Issue

Is hydrogen electronegativity higher than Pauling’s value? New clues from the 13C and 29Si NMR chemical shifts of [CHF3] and [SiHF3] molecules

Abstract

Introduction

Results and discussion

13C and 29Si δ NMR chemical shifts as a function of the Σ(rL ) values, in tetrahedral [AL4] (A=C, Si) systems with Σ(χLPau)≥12.4: the case of [AHmXn] compounds (Xn=combination of n halides; m+n=4)

Calculation of the NMR effective electronegativity value for the hydrogen atom, on the basis of the [CHF3] and [SiHF3] reference compounds

Conclusion

Experimental section

Influence of steric hindrance and electronegativity of atomic substituents on the 13C and 29Si NMR chemical shifts of [AHmXn] (A=C, Si; Xn=combination of n Cl and/or F halides; m+n=4) compounds

Article note

Acknowledgments

References

Supplementary Material

Journal and Issue

Articles in the same Issue

Is hydrogen electronegativity higher than Pauling’s value? New clues from the ¹³C and ²⁹Si NMR chemical shifts of [CHF₃] and [SiHF₃] molecules

¹³C and ²⁹Si δ NMR chemical shifts as a function of the Σ(r_{_L} ) values, in tetrahedral [AL₄] (A=C, Si) systems with Σ(χLPau)≥12.4: the case of [AH_mX_n] compounds (X_n=combination of n halides; m+n=4)

Calculation of the NMR effective electronegativity value for the hydrogen atom, on the basis of the [CHF₃] and [SiHF₃] reference compounds

Influence of steric hindrance and electronegativity of atomic substituents on the ¹³C and ²⁹Si NMR chemical shifts of [AH_mX_n] (A=C, Si; X_n=combination of n Cl and/or F halides; m+n=4) compounds