Electronegativities from Core-Ionization Energies:  Electronegativities of SF₅and CF₃

Abstract

Core-ionization energies have been measured for SF(6) (S 2p), SF(5)SF(5) (S 2p), SF(5)Br (S 2p and Br 3d), and SF(5)CF(3) (S 2p and C 1s). These results, together with others that establish correlations between core-ionization energies and Pauling electronegativities, make it possible to assign group electronegativities to SF(5) and CF(3). This method gives electronegativities for these groups comparable to that of bromine, whereas analysis of the effect of these groups on acidity indicates electronegativities comparable to that of fluorine. Other methods of estimating electronegativity fall between these extremes. These disparities can be understood in part as reflecting the effects of polarizibility of the substituent, which tends to lower both the core-ionization energy and the deprotonation energy, making the electronegativity appear to be less in one case and more in the other. In addition, and possibly more important, the core-ionization energies presented here reflect the effect of the group on an adjacent atom, whereas the acidity reflects the effect on a remote atom. It appears that fluorine has a large effect on an adjacent atom but a relatively small effect on a remote atom. By contrast SF(5) and CF(3) have a relatively small effect on an adjacent atom, but this effect falls off only slowly with distance from the substituent. Thus, the effective electronegativities of CF(3) and SF(5) relative to those of the halogens depend on the site at which the molecule is probed as well as on the process that is under consideration.

Conformational impact of pentafluorosulfanylation on acyclic aliphatic molecules

“…This has been further refined to a s I value for SF 5 of 0.55 and a s R value of 0.11 [10] in contrast to s I value for CF 3 of 0.39 and a s R value of 0.12 [11,12]. The diminished resonance and increased inductive contributions are consistent with the calculated dipole moments [13,14] of 2.5896 D and 3.556 D for the C-CF 3 and C-SF 5 bonds, respectively. This combination of effects likely amplifies dipolar and electrostatic interactions in pentafluorosulfanylated compounds.…”

Diastereoselectivity in the Staudinger reaction of pentafluorosulfanylaldimines and ketimines

“…The inductive σ I and σ R values for SF 5 , 0.55 and 0.11 [10], contrast with σ I and σ R values for CF 3 of 0.39 and 0.12 [11–12] illustrating the increased inductive effect of the SF 5 group relative to the CF 3 group. This effect can also be seen in the calculated dipole moments of 1,1,1-trifluoroethane and pentafluorosulfanylmethane of 2.589 and 3.556 Debye respectively [7–8]. When these electronic effects are combined with an occupied volume only slightly less than that of a tert -butyl group [3,13], the SF 5 group can have unanticipated influences on the structure such as anchoring side chain and neighboring hydroxy group conformations [14–15].…”

“…With pseudooctahedral geometry around sulfur, the SF 5 group is a unique substituent for the medicinal or pharmaceutical chemist. While the electron withdrawing properties of the SF 5 and CF 3 groups are similar [7–8], the electronegativity of the SF 5 group has been suggested to be as high as 3.65 in contrast to 3.36 for CF 3 [9]. The inductive σ I and σ R values for SF 5 , 0.55 and 0.11 [10], contrast with σ I and σ R values for CF 3 of 0.39 and 0.12 [11–12] illustrating the increased inductive effect of the SF 5 group relative to the CF 3 group.…”

Synthesis and herbicidal activity of a pentafluorosulfanyl analog of trifluralin

“…When the electronic influence of a SF 5 group is compared with that of a CF 3 group, the electron withdrawing effect, as assessed by the carbon 1s photoelectron spectra, is similar in magnitude. 7,8) However, the electronegativity of the SF 5 group has been proposed to be as high as 3.65 in comparison to a value of 3.36 for the CF 3 group. 9) In electrophilic substitution reactions the Hammet s p value for SF 5 was determined to be 0.68 in contrast to s p value for CF 3 of 0.54.…”

“…11,12) The decreased resonance and increased inductive contributions are consistent with the electronic effects observed in the estimation of electronegativity. 7,8) The organic chemistry of the SF 5 group, previously reviewed 6,13) and extensively developed by Gard, has only recently come under more widespread investigation with the ready availability of previously difficultly accessible building blocks or reagents. 14) To date pentafluorosulfanyl arenes have found applications in liquid crystalline displays 15,16) and in agrochemicals.…”