Anionic sigma complexes

Strauss, Michael J.

doi:10.1021/cr60268a003

Cited by 289 publications

(108 citation statements)

References 36 publications

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“…The chemistry of Meisenheimer complexes has a history stretching back more than 100 years and a tremendous amount of relevant work has been reported. Crystallography and NMR spectroscopy have played pivotal roles in the structural characterization of the -complexes [5] while visible spectroscopy has been the primary tool in kinetic and thermodynamic studies of complex-forming reactions in solution [6]. Except for theoretical investigations [7][8][9][10], very few studies have been reported on gas-phase Meisenheimer complexes, although gasphase nucleophilic reactions of aromatic systems [11][12][13][14] have been investigated.…”

Section: Eisenheimer Complexes First Proposed Bymentioning

confidence: 99%

Meisenheimer complexes bonded at carbon and at oxygen

Chen

Cooks

2004

J. Am. Soc. Mass Spectrom.

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The carbon-bonded gas-phase Meisenheimer complex of 2,4,6-trinitrotoluene (TNT) and the nitromethyl carbanion CH 2 NO 2 Ϫ (m/z 60) is generated for the first time by chemical ionization using nitromethane as the reagent gas. Collision-induced dissociation (CID) of the Meisenheimer complex furnishes deprotonated TNT, a result of the higher gas-phase acidity of TNT than nitromethane. The formation of Meisenheimer complexes with CH 2 NO 2 Ϫ in the gas phase is selective to highly electron-deficient compounds such as dinitrobenzene and trinitrobenzene and does not occur with organic molecules with lower electron-affinity such as methanol, methylamine, propionaldehyde, acetone, ethyl acetate, chloroform, toluene, m-methoxytoluene, and even nitrobenzene and p-fluoronitrobenzene. As such, the reaction allows selective detection of TNT in mixtures. Meisenheimer complexes between CH 2 NO 2 Ϫ and the three dinitrobenzene isomers display distinctive fragmentations. The oxygen-bonded -complex of TNT with the deprotonated hemiacetal anion CH 3 OCH 2 O Ϫ (m/z 61), represents a different type of Meisenheimer complex. It displays characteristic fragmentation involving loss of HNO 2 upon CID. The combination of a selective ion/molecule reaction (Meisenheimer complex formation) followed by a characteristic CID process provides a second novel and highly selective approach to the detection of TNT and closely related compounds in mixtures. The assay is readily implemented using neutral loss scans in a triple quadrupole mass spectrometer. Gas-phase reactions of denitrosylated TNT with benzaldehyde produce the corresponding dihydrofuran in an aldol condensation, a result that parallels the corresponding condensed-phase reaction. (J Am Soc Mass Spectrom 2004, 15, 998 -1004

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Section: Eisenheimer Complexes First Proposed Bymentioning

confidence: 99%

Meisenheimer complexes bonded at carbon and at oxygen

Chen

Cooks

2004

J. Am. Soc. Mass Spectrom.

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“…The increased stability of I : 1 as compared to 2: 1 sulfite ion -1-X-2,4,6-trinitrobenzene o-complexes in aqueous solutions of high dimethylsulfoxide content has been attributed to better solvation by dimethylsulfoxide than by water of the charge-delocalized 1: 1 o-complex (4,13).…”

Section: Resultsmentioning

confidence: 99%

“…Thus cyanide ion, which would be expected to have less stringent solvation requirements and give rise to much smaller steric strain effects than sulfite, reacts with 2,4,6-trinitrobenzaldehyde to yield only the C-1 complex even at low temperatures (5). It might be argued that, in the special case for which X = COH and the anion is sulfite ion, the electron withdrawing effect of the aldehyde group together with better solvation and coplanarity with the ring of the para nitro group and the possible release of steric compression (4,13) in the C-1 complex (1) relative to the parent compound might partially offset the more favorable steric and solvation requirements of the C-3 complex (2). As a result both isomeric complexes are observed.…”

Section: Resultsmentioning

confidence: 99%

“…studies suggest that the 1 : 1 complex could be either 1 or 2. Unfortunately, the visible absorption data cannot be used t o differentiate between these two possibilities (4,13,14).…”

Section: Resultsmentioning

confidence: 99%

“…This rate constant is very close to that reported by Bernasconi and Bergstrom (19) for the formation of the 1 : 1 sulfite ion -1,3,5-trinitrobenzene complex and is in the range of the specific rate constants observed for 1 : 1 o-complex formation between sulfite ion and picramide, N-methylpicramide, and N,N-dimethylpicramide. 4 For each of these four reactions sulfite ion attacks a t a hydrogen-bearing ring carbon. Studies using the T-jump technique are in progress in an attempt to obtain more extensive and more reliable kinetic data for both the fast and very fast reactions.…”

Section: Resultsmentioning

confidence: 99%

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The Interaction of Sulfite Ion with 2,4,6-Trinitrobenzaldehyde: Kinetic, Equilibrium, and Proton Magnetic Resonance Studies

Marendic¹,

Norris²

1973

Can. J. Chem.

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Sulfite ion reacts with 2,4,6-trinitrobenzaldehyde in aqueous solution of ionic strength 0.14 M to yield a 1 :1 o-con~plex at low sulfite concentrations and a 2: 1 o-complex at high sulfite concentrations. The visible absorption characteristics of these two o-complexes as well as equilibrium constants and relevant thermodynamic parameters for their formation have been determined. P.n~.r. studies demonstrate that two isomeric forms of the 1 : 1 o-complex occur in aqueous dimethylsulfoxide solution and two isomeric forms of the 2 : l o-complex occur in water. Iri both the 1 :1 and the 2 : l complexes isomers are found which contain sulfite ion attached to the C-1 carbon and one of the isomeric 2 : 1 o-complexes is postulated to exist in cis and trans forms. Observations are presented concerning the kinetics of the very rapid formation of the 1 :1 o-complex in water.L'ion si~lfite reagit avec la trinitro-2,4,6 benzaldehyde en solution aqileilse de force ioniqi~e 0.14 M pour donner iln complexe I : 1 a des concentrations faibles de si~lfite et iln coniplexe 2: 1 i des concentrations Clevees de sulfite. On a determine les caracteristiqi~es d'absorption de ces deux complexes ainsi qile les constantes d'kquilibres et les parametres thermodynaniiques-se rapportant a leur formation. Des etudes en r.m.p. ont montrt que deux fornies isomeriques du complexe 1 : 1 se forment en solution aqueuse de sulfoxyde de dimethyle et que deux fornies isomeriques du complexe 2:l se forment dans I'eai~. On a trouvk dans les deux coniplexes I : 1 et 2: 1 des isomtres qui contiennent l'ion sulfite relie ail carbone C-I. De meme on admet que I'un des con~plexes 2: 1 isomeriques existe sous des formes cis et trans. On prksente aussi des observations se rattachant a la cinetique de formation tres rapide du complexe 1 :

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