Mesomeric stabilization of carbonium ions by .alpha.-cyano groups. A theoretical evaluation of inductive vs. resonance effects of the cyano moiety

Dixon, David A.; Charlier, Patricia A.; Gassman, Paul G.

doi:10.1021/ja00531a051

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“…Thus they act as electron releasing on the cations and withdrawing on both radicals and anions depending on electron demand [5,[57][58][59][60][61][62][63].…”

Section: Electron Densitiesmentioning

confidence: 99%

A Theoretical Study of Monosubstituted Cyclopropenyl System

Yahya

Khalil

1992

Zeitschrift Für Naturforschung A

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MONDO-Forces calculations have been performed, with complete optimization of geometry on X-cyclopropenyl system (cations, radicals and anions), where X is H, O", OH, CH 3 , CN, N0 2 , F and CF 3 . All substituents prefer planar structure when substituted on both cations and radicals, while they prefer pyramidal structure in the case of anions except CF 3 . The substituents O", OH and F act as electron releasing, while CHO, N0 2 and CF 3 act as electron withdrawing when substituted on cyclopropenyl system. CH 3 and CN show amphielectronic behaviour. They act as electron releasing on the cations and withdrawing on both radicals and anions depending on electron demand. In the case of cations and radicals, all substituents were found to increase the vicinal bonds and decrease the distal bonds and bond angles to which the substituent is attached. For anions the substitutents show no such regularity because the substituents are out of the three-membered ring plane. All substituents increase the stability of the cyclopropenyl system except CF 3 in the case of the cation.The cyclopropenyl cation is the smallest aromatic molecule which has two ^-electrons and satisfies the Hückel 4 n + 2 rule. The electronic structure is of great interset since the molecule is highly strained but despite of this the ion is stable in the form of salts, e. g. C 3 H 3 • SbCl^, and also in polar solvents [1]. D 3h configuration of the ion is indicated by its IR and NMR spectra [1], Allen has reported a structural analysis for two cyclopropenyl cation derivatives based upon Xray crystallographic data [2]. Clark carried out ab initio LCAO SCF MO Calculations on both C 3 H 3 + and C3H3 and discussed the aromaticitiy and antiaromaticity [3]. Ha et al. reported an ab initio LCAO SCF MO investigation on C 3 H 3 + , C 3 Hj and C 3 H 3~ and discussed the geometry and stability of these species [4j. Random et al. aiso carried out ab initio calculations on C3H3 using STO-3G and 6-31G and obtained the equilibrium structure of the ion [5]. Takada and Ohno also published an ab initio CI calculation on the electronic structure of C3H3 [6]. The most recent ab initio calculations on the molecular structure and vibrational spectrum of C3H3 were performed by Xie et al. [7], and Lee et al. [8], Cyclopropenyl free radical, the simplest member of the series of fully conjugated cyclic radicals, has been the subject of experimental [9-13] and theoretical studies [4,[14][15][16][17][18][19][20],The theoretical work by Chipman and Miller [20] predicts an ethylenic structure of C s symmetry as the lowest energy form. The hydrogen atom at the apex of the isoceles triangle is bent substantially out of the ring plane. The allylic structure, which satisfies the Jahn-Teller theorem, is predicted to be 5 kcal/mole higher in energy. Experimental work by Closs and Redwine [13] support the C s structure and rules out the allylic structure. There is no experimental information on the properties of the neutral radical, so it is necessary to resort to theoretical studies.The cyc...

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“…Thus they act as electron releasing on the cations and withdrawing on both radicals and anions depending on electron demand [5,[57][58][59][60][61][62][63].…”

Section: Electron Densitiesmentioning

confidence: 99%

A Theoretical Study of Monosubstituted Cyclopropenyl System

Yahya

Khalil

1992

Zeitschrift Für Naturforschung A

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“…Prominent examples of such C-H acidic molecules include cyclopentadiene (C 5 H 6 ) and β-diketones (acetylacetone in its keto form). The C-H acidity of compounds of the general formula CH 3 X was shown to decrease in the order X = NO 2 Ͼ CHO Ͼ CN Ͼ CCH Ͼ CHCH 2 . [1] The cyanomethylene anion, (CH 2 CN) -, was already subject of a number of experimental and theoretical studies, evaluating in detail the inductive and resonance effects of the cyano moiety.…”

Section: Introductionmentioning

confidence: 99%

The First Cyanomethyl Complex of Gold, Synthesized by Reaction of a Au^I Complex with Acetonitrile in the Presence of a New Guanidine N‐Superbase

et al. 2010

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Herein we report on the synthesis of the new strong N‐base and electron donor tdmegb [1,2,4,5‐tetrakis(N,N′‐dimethylethyleneguanidino)benzene]. Compared to the previously synthesized ttmgb [1,2,4,5‐tetrakis(tetramethylguanidino)benzene], this compound turned out to be a slightly better electron donor and a slightly weaker base. In experiments in which [AuCl(PPH3)] was dissolved in CH3CN together with tdmegb, we observed the formation of the first cyanomethyl complex of Au, namely [Au(CH2CN)(PPh3)] in good yield. This reaction does not take place for ttmgb. Moreover, in CH2Cl2 solutions containing the three components [AuCl(PPh3)], tdmegb and a nitrile (in large excess), only AuI reduction leading to a [Au11Cl3(PPh3)7] cluster is observed. Possible reaction mechanisms for this unusual reaction are discussed.

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“…[2] does occur, thereby presumably lessening the extent of destabilization (10,23,24,26). Tables 1 and 2 extend these conclusions to di-and tria-cyano cations.…”

mentioning

confidence: 57%

“…Howhave been prepared or observed (e.g., 5 (12, 2 l), 6 (141,7 ever, numerous studies, both experimental (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and (1 8), and 8 (1 9)). theoretical (23)(24)(25)(26)(27)(28), have shown that this destabilizing efIn some instances, such as a-cyano and a-keto carbocations, this unexpected level of stability can be attributed to '~u t h o r to whom correspondence may be addressed.…”

Section: Introductionmentioning

confidence: 99%

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Computational determination of the relative stabilities of some nitro carbocations

Redfern¹,

Murray²,

Politzer³

1992

Can. J. Chem.

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The relative stabilities of a group of nitro carbocations (derivatives of the methyl, cyclopropyl. and cyclopropenyl cations) are determined by means of trb irziiio SCF/3-2 I G calculations, and compared to the corresponding results for other substituent groups, both electron donating and withdrawing. The a-nitro carbocations are generally destabilized relative to the parent cation, but often to a lesser extent than anticipated from the strongly electron-withdrawing nature of NOZ. ' The optimized structures indicate that this is due to the stabilizing fomiation of an intramolecular ring involving the nitro group; however, this requires the proximity of a sufficiently positive carbon.Key Utilisant des mkthodes ab iniiio SCF/3-2 1 G , on a calculC les stabilitks relatives d'un certain nonibre de carbocations de derives nitres (derives des cations mkthyle, cyclopropyle et cyclopropCnyle) et on les a comparCes aux resultats correspondants obtenus avec d'autres substituants, tant Clectro-attracteurs que electro-donneurs. Les carbocations en a d'un nitro sont gCnCralement dCstabilisCs par rapport au cation parent; toutefois, ils le sont souvent nioins que ce qui avait tte anticipe sur la base de la nature tres electro-attractive du NO2. Les structures optimisees indiquent que ce resultat est dfi a la formation stabilisante d'un cycle intranioleculaire impliquant le groupe nitro; toutefois, ce cycle nkcessite la proximite d'un carbone suffisamment positif.

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Mesomeric stabilization of carbonium ions by .alpha.-cyano groups. A theoretical evaluation of inductive vs. resonance effects of the cyano moiety

Cited by 50 publications

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A Theoretical Study of Monosubstituted Cyclopropenyl System

A Theoretical Study of Monosubstituted Cyclopropenyl System

The First Cyanomethyl Complex of Gold, Synthesized by Reaction of a Au^I Complex with Acetonitrile in the Presence of a New Guanidine N‐Superbase

Computational determination of the relative stabilities of some nitro carbocations

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Mesomeric stabilization of carbonium ions by .alpha.-cyano groups. A theoretical evaluation of inductive vs. resonance effects of the cyano moiety

Cited by 50 publications

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A Theoretical Study of Monosubstituted Cyclopropenyl System

A Theoretical Study of Monosubstituted Cyclopropenyl System

The First Cyanomethyl Complex of Gold, Synthesized by Reaction of a AuI Complex with Acetonitrile in the Presence of a New Guanidine N‐Superbase

Computational determination of the relative stabilities of some nitro carbocations

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The First Cyanomethyl Complex of Gold, Synthesized by Reaction of a Au^I Complex with Acetonitrile in the Presence of a New Guanidine N‐Superbase