Studies on the decomposition of tetra-alkylammonium salts in solution. Part II. Dependence of the activation parameters on the structure of the substrate

Can. J. Chem. 53, 3216 (1975).A kinetic study of the nucleophilic substitution reactions of a series of para-substituted phenylbenzyldimethylammonium nitrates with sodium thiophenoxide at 0 "C in N,N-dimethylformamide containing a large excess of sodium nitrate, has shown the reaction to be a secondorder process which is first-order in both the substrate and the nucleophile. A Hammett p value of +2.04 for different para-substitutents on the N-phenyl group of the quaternary ammonium salt and a large nitrogen kinetic isotope effect of 1.0200 + 0.0007 have excluded any mechanism involving a carbonium ion intermediate but are in accord with an SN2 mechanism with a substantial amount of carbon-nitrogen bond rupture in the transition state.KENNETH CHARLES WESTAWAY et RAYMOND ALCIDE POIRIER. Can. J. Chem. 53,3216 (1975). Une etude cinetique des reactions de substitution nucleophile d'une s6ie de nitrates dep-Xphenylbenzyldimethylammonium par le thiophenolate de sodium, i 0 "C dans la N,N-dimethylformamide contenant un grand ex& de nitrate de sodium, a permis de ddmontrer que la reaction est du deuxieme ordre soit du premier ordre dans chacun des reactifs. Sur la base (a) d'une valeur p de Hammett de +2.04 pour differents substituants en para du groupement phdnyle du sel d'ammonium quaternaire et (b) d'un grand (1.0200 + 0.0007) effet isotopique cinetique de l'azote, on peut exclure tout mkanisme impliquant un intermediaire carbocationique; toutefois les resultats sont en accord avec un mecanisme SN2 impliquant une portion importante de rupture du lien carbone-azote dans I'etat de transition.[Traduit par le journal] IntroductionMore recently, Leffek andco-workers (5-7) have Several authors (1-7) have studied the nucleo-studied these reactions in the dipolar aprotic philic substitution reactions of quaternary am-solvents chloroform and acetone and have conmonium ions cluded on the basis of an extensive kinetic study

Section: Hammett P Valuementioning

confidence: 79%

“…The p-methoxy-N,N-dimethylaniline was prepared from p-anisidine using the method described by Leffek (18). The p-chloro-N,N-dimethylaniline was prepared from p-chloroaniline using the method described by Chambers (27).…”

Section: Methodsmentioning

confidence: 99%

Isotope Effects in Nucleophilic Substitution Reactions. I. The Mechanism of the Reaction of Phenylbenzyldimethylammonium Ion with Thiophenoxide Ion

Westaway¹,

Poirier²

1975

“…These isotope effects are considerably larger than those observed for SN2 reactions and Leffek and KO very reasonably concluded that these reactions must involve the formation of a carbonium ion intermediate in the slow step of the reaction. Based on this and other evidence (8,9) these authors proposed that the reacZThe magnitudes of secondary a-deuterium kinetic isotope effects for SN2 reactions will also be affected by a change in the nucleophile.…”

Section: Table 1 Maximum Secondary A-deuterium Kineticmentioning

confidence: 93%

Isotope effects in nucleophilic substitution reactions. II. Secondary α-deuterium kinetic isotope effects: a criterion of mechanism?

Westaway¹,

Ali²

1979

A very large secondary a-deuterium kinetic isotope effect of 1.179 i 0.007 (1.086 i 0.003 per a-deuterium) has been observed for the SN2 reactlon of thlophenoxide ion with benzyldimethylphenylammonium ion in D M F at 0°C. This large isotope effect which is far outside the range reported for SN2 reactions, is attributed to the fact that the extraordinarily large steric crowding around the Ca-H bonds in the substrate is reduced in the SN2 transition state. The structure of the transition state is shown to be consistent with this hypothesis.KENNETH CHARLES WESTAWAY et SYED FASAHAT ALI. Can. J. Chem. 57, 1089(1979). Dans la reaction SN2 de l'ion thiophenolate avec l'ion benzyldimethylphenylamn~oi~ium dans le D M F a O°C, on a observe un effet isotopique cinttique secondaire du deuterium en alpha qui est tres grand 1.179 + 0.007 (1.086 i 0.003 par deuterium a). Cet effet isotopique important, qui est a l'exterieur des valeurs rapportees pour des reactions SN2, peut btre attribue au fait que l'encombrement sttrique qui est particulierement important au niveau des liaisons Ca-H dans le substrat est reduit dans l'etat de transition SN2. On demontre que la structure de I'etat de transition est en accord avec cette hypothese.[Traduit par le journal]

“…Leffek and co-workers have extensively studied the decomposition of aralkyldimethylphenylammonium halides to aralkyl halides and dimethylaniline (the reverse of the Menschutkin reaction) in chloroform (1)(2)(3)(4)(5), eq. [I].…”

Section: Introductionmentioning

confidence: 99%

Isotope effects in nucleophilic substitution reactions. V. The mechanism of the decomposition of 1-phenylethyldimethylphenylammonium halides in chloroform

Joly¹,

Westaway²

1986

Secondary a and P hydrogen-deuterium kinetic isotope effects have been used together to show that the SN reaction between 1-phenylethyldimethylphenylammonium ion and bromide or iodide ion in chloroform occurs by way of an SN2 mechanism within a triple ion in spite of the fact that it reacts faster than the primary substrate, benzyldimethylphenylamrnonium bromide. The very loose transition state and steric effects in the ground state appear to be responsible for the unusually fast SN2 reactions between 1-phenylethyldimethylphenylammonium ion and halide ions in chloroform.HELEN ALMA JOLY et KENNETH CHARLES WESTAWAY. Can. J. Chem. 64, 1206Chem. 64, (1986.On a fait appel h une combinaison des effets isotopiques cinCtiques secondaires des hydrogknes et (ou) deutCriums en a ainsi qu'en p pour montrer que le mCcanisme de la rkaction SN qui se produit dans le chloroforme entre l'ion dimCthyl phCnyl-1 kthyl phCnylammonium et les ions bromure ou iodure est SN2, dans un ion triple, et ce en dCpit du fait que cette r6action soit plus rapide que celle du substrat primaire, le bromure de benzyl dimkthyl phCnylammonium. 11 semble que 1'Ctat de transition trks lsche et que les effets sttriques dans 1'6tat fondamental soient responsables pour la kaction SN2 exceptionnellement rapide des halogknures de dimCthyl phtnyl-1 Cthyl phCnylammonium dans le chloroforme.[Traduit par la revue]