The Electrical Effect of the Trifluoromethyl Group

Roberts, John D.; Webb, Richard L.; McElhill, Elizabeth A.

doi:10.1021/ja01157a111

Cited by 142 publications

(65 citation statements)

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“…This zwitterionic representation of B Model is also the dominant Lewis resonance structure within the natural resonance theory (NRT) formalism (Figure 4a). In line with analysis by Müller and co-workers [62], the short Si-S bond and the Wiberg bond index of 1.38 can be rationalized by negative hyperconjugation [64,65] of the sulphur lone pairs into the σ*(Si-R) orbitals: the occupancy of the LP(S) NBOs is significantly decreased (1.81 e, 1.76 e), while the NBOs for the anti-bonding σ*-orbitals are partly populated (Si-H: 0.11 e, Si-C NHC : 0.14 e, Si-C mTer : 0.12 e). Topological analysis of the computed electron density, by means of Bader's quantum theory of atoms in molecules (QTAIM) [66,67], characterizes the Si-S bond as a strongly polar covalent interaction as indicated by a marked shift of the bond-critical point (bcp) towards the more electropositive Si site, a relatively large electron density ρ bcp , a positive Laplacian ∇ 2 ]ρ bcp as well as a negative total energy density H bcp at the bcp (Figure 4c) [68,69].…”

Section: Reaction Of Silyliumylidene a With H2ssupporting

confidence: 72%

S–H Bond Activation in Hydrogen Sulfide by NHC-Stabilized Silyliumylidene Ions

et al. 2018

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Reactivity studies of silyliumylidenes remain scarce with only a handful of publications to date. Herein we report the activation of S-H bonds in hydrogen sulfide by mTer-silyliumylidene ion A (mTer = 2,6-Mes 2 -C 6 H 3 , Mes = 2,4,6-Me 3 -C 6 H 2 ) to yield an NHC-stabilized thiosilaaldehyde B. The results of NBO and QTAIM analyses suggest a zwitterionic formulation of the product B as the most appropriate. Detailed mechanistic investigations are performed at the M06-L/6-311+G(d,p)(SMD: acetonitrile/benzene)//M06-L/6-311+G(d,p) level of density functional theory. Several pathways for the formation of thiosilaaldehyde B are examined. The energetically preferred route commences with a stepwise addition of H 2 S to the nucleophilic silicon center. Subsequent NHC dissociation and proton abstraction yields the thiosilaaldehyde in a strongly exergonic reaction. Intermediacy of a chlorosilylene or a thiosilylene is kinetically precluded. With an overall activation barrier of 15 kcal/mol, the resulting mechanistic picture is fully in line with the experimental observation of an instantaneous reaction at sub-zero temperatures.

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Section: Reaction Of Silyliumylidene a With H2ssupporting

confidence: 72%

S–H Bond Activation in Hydrogen Sulfide by NHC-Stabilized Silyliumylidene Ions

et al. 2018

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“…Negative hyperconjugation is one of the fundamental concepts in organic chemistry [1][2][3][4][5][6][7][8][9][10][11][12][13] and has been utilized for interpretation of many phenomena such as stabilities of conformers, [14,15] anomeric effect, [16] and strong electronwithdrawing ability of the polyfluorinated alkyl group. [1,13] However, it is difficult to determine experimentally the strength of negative hyperconjugation.…”

Section: Introductionmentioning

confidence: 99%

“…[1,13] However, it is difficult to determine experimentally the strength of negative hyperconjugation. Recently, we evaluated the magnitude of β-fluorine negative hyperconjugation effect, ΔG o β-F , involved in the gas-phase acidity of polyfluorinated alkanes and aryl-substituted fluoroalkanes on the basis of an empirical approach.…”

Section: Introductionmentioning

confidence: 99%

A natural bond orbital analysis of aryl‐substituted polyfluorinated carbanions: negative hyperconjugation

Suenaga

Nakata

Abboud

et al. 2017

J of Physical Organic Chem

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Aryl-substituted polyfluorinated carbanions, ArCHR f − where R f = CF 3 (1), C 2 F 5 (2), i-C 3 F 7 (3), and t-C 4 F 9 (4), were analyzed by means of the natural bond orbital (NBO) theory at the B3LYP/6-311+G(d,p) computational level. A lone pair NBO at the formal anionic center carbon (Cα) was not found in the Lewis structure. Instead, significant donor/acceptor NBO interactions between π(Cα-C1) and σ*(Cβ-F) or σ*(Cβ-Cγ)were observed for 1, 2, 3a (strong electron-withdrawing substituent, from p-CF 3 to p-NO 2 ), and 4. Their second-order donor/acceptor perturbation interaction energy, E(2), values decreased with the increase of the stability of carbanions. A larger E(2) value corresponds to longer Cβ-F and Cβ-Cγ bonds and a shorter Cα-Cβ bond, indicating that the E(2) values can be associated with the negative hyperconjugation of the Cβ-F and Cβ-Cγ bonds. In accordance with this, the E(2) values for π(Cα-C1) ! σ* (Cβ-F) were linearly correlated with the ΔG o β-F values (an empirical measure of β-fluorine negative hyperconjugation obtained from an increased acidity). In 3b (weak electron-withdrawing substituents, from H to m-NO 2 ) very large E(2) values for LP (Fβ) ! π*(Cα-Cβ) were obtained. This was attributed to the Cβ-F bond cleavage and the Cα-Cβ double bond formation in the Lewis structure that is caused by the extremely strong negative hyperconjugation of the Cβ-F bond.KEYWORDS donor/acceptor NBO interaction energy, natural bond orbital analysis, negative hyperconjugation, polyflourinated carbanions

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“…However, this type of interaction exists not only in glucosides but are prevalent throughout chemistry. Roberts et al [23] first used negative hyperconjugation (also referred to as double-bond no-bond resonance) to explain electrical effects in trifluoromethyl groups. Dewar examined negative hyperconjugation (p p !…”

Section: Introductionmentioning

confidence: 99%

What governs nitrogen configuration in substituted aminophosphines?

Wodrich

Vargas

Morgantini

et al. 2008

J of Physical Organic Chem

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The trigonal planar geometry of the nitrogen atom in commonly used phosphoramidite ligands is not in line with the traditional valence shell electron pair repulsion (VSEPR) model. In this work, the effects governing nitrogen configuration in several substituted aminophosphines, A 2 PNB 2 (A or B ¼ H, F, Cl, Br, Me, OMe, BINOP), are examined using modern computational analytic tools. The electron delocalization descriptions provided by both electron localization function (ELF) and block localized wavefunction analysis support the proposed relationships between conformation and negative hyperconjugative interactions. In the parent H 2 PNH 2 , the pyramidal nitrogen configuration results from nitrogen lone pair electron donation into the s * P-H orbital. While enhanced effects are seen for F 2 PNMe 2 , placing highly electronegative fluorine substituents on nitrogen (i.e., Me 2 PNF 2 ) eliminates delocalization of the nitrogen lone pair. Understanding and quantifying these effects can lead to greater flexibility in designing new catalysts.

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The Electrical Effect of the Trifluoromethyl Group

Cited by 142 publications

References 0 publications

S–H Bond Activation in Hydrogen Sulfide by NHC-Stabilized Silyliumylidene Ions

S–H Bond Activation in Hydrogen Sulfide by NHC-Stabilized Silyliumylidene Ions

A natural bond orbital analysis of aryl‐substituted polyfluorinated carbanions: negative hyperconjugation

What governs nitrogen configuration in substituted aminophosphines?

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