The ρ-ρ Relation and Transmission of Electronic Effects in the Reaction of Phenylacetic Acids with Diphenyldiazomethane

J of Physical Organic Chem

et al. 2014

The gas-phase acidity (GA) values were determined for a number of perfluoroalkyl-substituted sulfonylimides by measuring proton-transfer equilibria using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The GA scale below 286.5 kcal mol À1 for (CF 3 SO 2 ) 2 NH was extended and partially revised. The GA value of (C 4 F 9 SO 2 ) 2 NH which is currently the strongest acid was revised from 284.1 to 278.6 kcal mol À1 . The effect of fluorine atoms on the acidity of perfluoroalkylsubstituted sulfonylimides was described with the following model N (γ) , and N (δ) are the numbers of fluorine atoms at α, β, γ, and δ position in R f SO 2 (R f = perfluoroalkyl group), respectively. This correlation indicates that the electron-withdrawing ability of the R f SO 2 group can be described in terms of the number of fluorine atoms in the perfluoroalkyl group corrected by taking into account their positions.

Section: Resultsmentioning

confidence: 66%

GA = ρ ({italicN}_{()(, α)} + b {italicN}_{()(, β)} + c {italicN}_{()(, γ)} + d {italicN}_{()(, δ)}) + e

where GA is the gas‐phase acidity, and N (α) , N (β) , N (γ) , and N (δ) are the numbers of fluorine atoms at α, β, γ, and δ position of the SO 2 group, respectively.…”

Section: Resultsmentioning

confidence: 99%

Gas‐phase acidity of bis[(perfluoroalkyl)sulfonyl]imides. Effects of the perfluoroalkyl group on the acidity

Zhang

Sonoda

J of Physical Organic Chem

et al. 2014

“…The effect of the R f group on acidity of PhC H ClR f and PhC H FR f , where R f is the tertiary fluoroalkyl group, would be determined by the accumulated inductive effect of fluorine atoms contained in the R f moiety and by the polarizability of the R f group depending on its size because the β‐fluorine negative hyperconjugation is absent in the acid's conjugate anions. Because the inductive effects of fluorine atoms on the stability of the conjugate anions should depend on the distance (or the number of insulating carbon atoms) between a formal anionic center and fluorine and on the number of fluorine atoms contained in the fluorinated alkyl group, and we previously proposed an empirical Eq. as a simple approximation for prediction of gas‐phase acidities of polyfluorinated alkanes having no β‐fluorine …”

Section: Resultsmentioning

confidence: 99%

Gas‐phase Acidities of 2‐Aryl‐2‐chloro‐1,1,1‐trifluoroethanes and Related Compounds. Experimental and Computational Studies

J of Physical Organic Chem

Abboud

Fujio

et al. 2016

The gas‐phase acidities (GA) of 2‐aryl‐2‐chloro‐1,1,1‐trifluoroethanes (1a), 2‐aryl‐2‐fluoro‐1,1,1‐trifluoroethanes (2a), and related compounds, XC6H4CH(Z)R where Z = Cl (1) or F (2) and R = C2F5 (b), t‐C4F9 (c), C(CF3)2C2F5 (d), C(CF3)2Me (e), Me (f), H (g), were investigated experimentally and computationally. On the basis of an excellent linear correlation (R2 > 0.99) of acidities of 1c, 1d, 1e, 1f and 2c, 2d, 2e, 2f where there is no fluorine atom at β‐position to the deprotonation site with the corrected number of fluorine atoms contained in the fluorinated alkyl group, the extent of β‐fluorine negative hyperconjugation of the CF3 and C2F5 groups (ΔGoβ‐F) was evaluated. The GAel values given by subtraction ΔGoβ‐F from the apparent GA value were considered to represent the electronic effect of the substituent X. The substituent effects on the GAel values and GA values for 1c, 1d, 1e, 1f and 2c, 2d, 2e, 2f were successfully analyzed in terms of the Yukawa–Tsuno equation. The variation of resonance demand parameter r− with the R group observed for various XC6H4CH(Z)R was linearly related to the GA (GAel) value of the respective phenyl‐substituted fluorinated alkanes. On the other hand, the corresponding correlation for the ρ values provided three lines for ArCH(Cl)R, ArCH(F)R and ArCH2R, respectively. These results supported our previous conclusion that the r− and ρ values are governed by the thermodynamic stability of the parent ion (ring substituent = H). Other factors arising from an atom bonded to the acidic center also influence the ρ value. Copyright © 2016 John Wiley & Sons, Ltd.

“…The acidity of C H 3 C(R f 1 )(R f 2 )R f 3 and PhC H 2 C(R 1 )(R 2 )R 3 should be determined by the accumulated inductive effect of fluorine atoms contained in the R f moiety and by the polarizability of the R f group depending on its size, because the β‐fluorine negative hyperconjugation is absent in the conjugate anions of such carbon acids having no β‐fluorine atom. Because the inductive effects of fluorine atoms on the stability of the acid's conjugate anions should depend on the distance (or number of insulating carbon atoms) between a formal anionic center and fluorine and on the number of fluorine atoms contained in the polyfluorinated hydrocarbon, we proposed an empirical approach Eqn for prediction of gas‐phase acidity

G A = ρ^{F} true(N_{(β)} prefix+ a N_{(γ)} prefix+ b N_{(δ)} true) prefix+ c

where N (β) , N (γ) , and N (δ) are numbers of fluorine atoms at β, γ, and δ positions of the formal negative charge center, respectively.…”

Section: Resultsmentioning

confidence: 99%

Substituent effects on acidity of aryl-substituted fluoroalkanes: a computational study

Abboud

2015

J. Phys. Org. Chem.

The gas‐phase acidities (GA) of various aryl‐substituted fluoroalkanes, XC6H4CH(R1)R2, were calculated at the B3LYP/6‐311 + G(d,p)//B3LYP/6‐311 + G(d,p). The acidity values of alkanes having a common substituent X varied significantly with the change of R1 and R2. Their changes in acidity of 1 and 2 having two strong electron‐withdrawing groups (CF3 or C2F5) at the deprotonation site and 8, 9, 10, 11 having no fluorine atom at β‐position were linearly correlated with the corrected number of fluorine atoms contained in the fluorinated alkyl group (R2 > 0.999). On the other hand, the GA values of β‐fluorine substituted alkanes (3, 4, 5, 6, 7) deviated in a stronger acid direction from the line. The enhanced acidity was attributed to the additional stabilization of the conjugate anion caused by the β‐fluorine negative hyperconjugation. The magnitude of β‐fluorine negative hyperconjugation of the fluorinated alkyl group (ΔGoβ‐F) given by the deviations from the line decreased with increasing electron‐withdrawing ability of substituent X on the benzene ring, indicating that β‐fluorine negative hyperconjugation competes with the electronic effect of the substituent X. The GAel values obtained by subtraction ΔGoβ‐F from the apparent GA value were successfully correlated in terms of the Yukawa–Tsuno equation. The obtained ρel and r−el values were linearly related to the GAel value of the respective phenyl‐substituted fluoroalkanes, supporting our previous conclusion that the ρ and r− values for the substituent effect caused by the electronic effects of the substituent on the acidity are determined by the thermodynamic stability of the parent ion (ring substituent = H). Copyright © 2015 John Wiley & Sons, Ltd.