AB initio electron density analysis of β-fluoroethyl anion: The non-importance of anionic fluorine hyperconjugation

Streitwieser, Andrew; Berke, Carl M.; Schriver, George W.; Grier, David L.; Collins, John B.

doi:10.1016/0040-4020(81)85071-5

Cited by 26 publications

(21 citation statements)

References 48 publications

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“…Similarly, an acidifying effect of 6.3 kcal mol ¹1 for the second substitution larger than the first one (3.0 kcal mol ¹1 ) was observed for CF 3 CH 3 . These results are not consistent with a general observation that a successive replacement by the electronwithdrawing group shows a smaller effect with the increasing (32) (i -C 3 F 7 ) 2 (C 2 F 5 )CH(4) (29) Corrected number of fluorine atoms Gas-phase acidity/kcal mol -1 12 C 3 F 7 CH 3 (26) bridgehead carbon acids number of substituent as seen in the effect of the CF 3 group. The unusual effect of α-fluorine substitution suggests that the electron-withdrawing effect of fluorine arising from its high electronegativity and the destabilizing effect caused by pp lone pair repulsion between a lone pair orbital and p-orbital of fluorine vary with carbanion.…”

Section: Discussioncontrasting

confidence: 75%

Gas-Phase Acidity of Polyfluorinated Hydrocarbons. Effects of Fluorine and the Perfluoroalkyl Group on Acidity

Zhang

Badal

Pasikowska

et al. 2014

Bulletin of the Chemical Society of Japan

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Gas-phase acidities of polyfluorinated hydrocarbons have been determined by measuring proton-transfer equilibria and by computing the free energies of deprotonated carbanions and the corresponding neutrals. An excellent linear relationship between acidities and the accumulated inductive effects of fluorine atoms contained in a molecule was observed for the perfluoroalkyl-substituted neopentanes,)CCH 3 , and polyfluorinated bridgehead carbon acids where the contribution of negative hyperconjugation of the C β F bond to the stability of the conjugate anions is absent or negligibly small. On the basis of this relationship, the extent of β-fluorine negative hyperconjugation involved in acidities of polyfluorinated hydrocarbons could be evaluated quantitatively. The negative hyperconjugation was found to be negligibly small in the stable tertiary polyfluorinated carbanions while in the less stable primary and secondary carbanions the contribution of this effect is present certainly, indicating that the negative fluorine hyperconjugation is complementary to the stabilization by the accumulated inductive effect of fluorine atoms. The extent of negative hyperconjugation was found to increase in order of CF 3 CH 2 ¹ < C 2 F 5 CH 2 ¹ μ C 3 F 7 CH 2 ¹ < i-C 3 F 7 CH 2 ¹ , being qualitatively consistent with the elongation of the C β F bond by deprotonation. The effect of α-fluorine on acidity was found to change complicatedly with the carbanion, e.g., the α-fluorine substitution in CF 3 CH 3 strengthens acidity, no effect in (CF 3 ) 2 CH 2 , and strengthens again acidity in (i-C 3 F 7 ) 2 CH 2 . Such varying effect of α-fluorine in the polyfluorinated hydrocarbons would be caused by a subtle balance of effective electronegativity of an anionic center carbon, a varying pp lone pair repulsion depending on the net negative charge at the formal charge center carbon, and the change in ability of β-F negative hyperconjugation caused by α-F substitution.

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Section: Discussioncontrasting

confidence: 75%

Gas-Phase Acidity of Polyfluorinated Hydrocarbons. Effects of Fluorine and the Perfluoroalkyl Group on Acidity

Zhang

Badal

Pasikowska

et al. 2014

Bulletin of the Chemical Society of Japan

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“…Streitweiser et al ( 5 ) supported the polarization idea by showing that there was no charge transfer involved. In reply to this, Schleyer and Kos (4) disagreed with the conclusions of Streitweiser et al and stated that the definition of hyperconjugation is the interaction of orbitals, independent of charge transfer, but that both charge transfer and polarization can be the result of hyperconjugation.…”

Section: Introductionsupporting

confidence: 55%

The anomeric effect in anionic systems XH_m-CH₂-NH⁻ and XH_m-CH₂-CH₂⁻, with XH_m = F, OH, NH₂ and CH₃

Scott¹,

Grein²

1994

Can. J. Chem.

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. Can. J. Chem. 72,2521Chem. 72, (1994.Ab initio geometry optimizations were performed at the RHFl6-3 1+G2: level on anionic acetal-like systems of the form XH,,,-CHI-NH-and XH,-CH,-CH,-, with XH,,, = F, OH, NH,, and CH,. Using Fourier analysis combined with energy decomposition methods, the electronic part of the anomeric stabilization, e, has been evaluated. For the NH-systems, eN-was calculated to be -1 6.5 for F, -5.2 for OH, -2.7 for NH,, and -1 . O for CH,. For the CH,-systems the ec-values are -8.1 for F, -5.3 for OH, -3.0 for NH, and -1.2 for CH,. The units are kcal/mol. Comparing the trends in calculated energies, bond distances, and charges with those obtained for the model compounds CH,-NH and CH,-CH,, the anomeric effect can be understood as the tendency of the anion to form a IT-bond in the CH,-NH-or CH,-CH,-portion of the nlolecule, caused by charge transfer from this portion to XH,,,. The CH,-CH,-NH-and CH,-CH,-CH, systems form an exception.CAMTLLA SCOTT et FRIEDRICH GREIN. Can. J. Chem. 72,252 1 (1994).On a effectut des optimisations ah initio de gComCtries au niveau RHFl6-3 l+G:Qur des systkmes ressemblant a des acCtals des formes XH,,,-CH,-NH-et XH,,,-CH,-CH,-dans lesquelles XH,,, = F, OH, NH, et CH,. Faisant appel a une analyse de Fourier combinCe avec des mCthodes de dCcomposition d'Cnergie, on a CvaluC la partie anomCrique de la stabilisation, e. Pour les systkmes NH-, on a CvaluC que les valeurs de eN-sont -16,5 pour F, -5,2 pour OH, -2.7 pour NH, et -1,O pour CH,. Pour les systkmes CH,-les valeurs de e,-sont -8,l pour F, -5,3 pour OH, -3.0 pour NH, et -1,2 pour CH,. Les unites sont les kcallmol. Une comparaison des tendances dans les Cnergies, les longueurs de liaisons et les charges calculCes avec les valeurs correspondantes obtenues pour les composCs modkles CH,-NH et CH,-CH,, on peut comprendre l'effet anomCrique comme une tendance de l'anion former une liaison IT dans les portions CH,-NH-ou CH,-CH,-des molCcules, provoquCe par un transfert de charge de cette portion au XH,,,. Les systkmes CH,-CH,-NH-et CH,-CHI-CH2-forment une exception.[Traduit par la rCdaction]

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“…In terms of molecular orbital theory, the β-fluorine negative hyperconjugation was attributed to orbital interaction of the formal lone pair at the anionic center with the σ* orbital of the C β -F bond. [10][11][12][13][14][15][16][17][18][19] This interaction stabilizes the negative charge of the conjugate anion, resulting in the increase of the acidity of polyfluorinated alkanes. Accordingly, such behavior of resonance effect involved in the δΔG o β-F value suggests that overlapping of a lone pair orbital of anionic center with the σ* orbital of the C β -F bond competes with that with π-orbitals of the aromatic moiety.…”

Section: Resultsmentioning

confidence: 99%

“…[6][7][8][9] Strong acidity characteristic of these compounds was considered to result from the stabilization of the conjugate anion by β-fluorine negative hyperconjugation in addition to strong inductive effect of the polyfluorinated alkyl group. [10][11][12][13][14][15][16][17][18][19][20] In this connection, we found recently that the magnitude of β-fluorine negative hyperconjugation involved in the gas-phase acidity (GA) of PhCH 2 R f increases in the order of R f = CF 3 < CHF 2 < CH 2 F by 5.8 kcal mol À1 and CF 3 < C 2 F 5 < CF(R f ) 2 by 9.5 kcal mol À1 . [21] On the other hand, in the p-nitrophenyl-substituted fluorinated alkanes, the βfluorine negative hyperconjugation of these fluorinated alkyl groups was reduced significantly.…”

Section: Introductionmentioning

confidence: 99%

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

Mishima

Abboud

2015

J. Phys. Org. Chem.

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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.

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AB initio electron density analysis of β-fluoroethyl anion: The non-importance of anionic fluorine hyperconjugation

Cited by 26 publications

References 48 publications

Gas-Phase Acidity of Polyfluorinated Hydrocarbons. Effects of Fluorine and the Perfluoroalkyl Group on Acidity

Gas-Phase Acidity of Polyfluorinated Hydrocarbons. Effects of Fluorine and the Perfluoroalkyl Group on Acidity

The anomeric effect in anionic systems XH_m-CH₂-NH⁻ and XH_m-CH₂-CH₂⁻, with XH_m = F, OH, NH₂ and CH₃

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

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AB initio electron density analysis of β-fluoroethyl anion: The non-importance of anionic fluorine hyperconjugation

Cited by 26 publications

References 48 publications

Gas-Phase Acidity of Polyfluorinated Hydrocarbons. Effects of Fluorine and the Perfluoroalkyl Group on Acidity

Gas-Phase Acidity of Polyfluorinated Hydrocarbons. Effects of Fluorine and the Perfluoroalkyl Group on Acidity

The anomeric effect in anionic systems XHm-CH2-NH− and XHm-CH2-CH2−, with XHm = F, OH, NH2 and CH3

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

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The anomeric effect in anionic systems XH_m-CH₂-NH⁻ and XH_m-CH₂-CH₂⁻, with XH_m = F, OH, NH₂ and CH₃