Large concentration effects on the magnitude of secondary alpha-deuterium kinetic isotope effects

Westaway, Kenneth Charles; Waszczylo, Zbigniew; Smith, Peter J.; Rangappa, Kanchugarakoppal S.

doi:10.1016/s0040-4039(00)98456-9

Cited by 11 publications

(3 citation statements)

References 12 publications

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“…The concentration dependence found for the secondary a-deuterium kinetic isotope effect in the SN2 (2) reaction between sodium thiophenoxide and n-butyl chloride was tentatively attributed to a change in the form of the reacting ion from a sodium thiophenoxide ion pair to a free thiophenoxide ion (1). Conductivity measurements (3), nrnr spectroscopy (4,5), and uv spectroscopy (6,7) have been used to study the phenomenon of ion pairing.…”

Section: Proof Of An Ion Pair and Afree Ion Reactionmentioning

confidence: 99%

Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of S_N2 reactions

Westaway¹,

Lai²

1988

Can. J. Chem.

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Spectroscopic and conductivity studies of sodium thiophenoxide solutions in four different solvents and the secondary a-deuterium kinetic isotope effects found in the presence of 15-crown-5 ether demonstrate that the secondary a-deuterium kinetic isotope effect and transition state structure for the SN2 reaction between sodium thiophenoxide and n-butyl chloride are significantly different, depending on whether the ionic reactant is a solvent-separated ion-pair complex or a free ion. In all three solvents in which the form of the ionic reactant changes, a smaller isotope effect and tighter transition state are found for the reaction with the ion-pair complex.KENNETH CHARLES WESTAWAY et ZHU-GEN LAI. Can. J. Chem. 66, 1263 (1988).On a rkalisk des Ctudes basCes sur la spectroscopic ou sur la conductivitk de solutions de thiophknolate de sodium dans quatre solvants diffCrents et on a mesurC des effets isotopiques cinCtiques secondaires des deuterium en a en prksence d'kther 15-couronne-5; I'ensemble de ces rksultats dCmontre que l'effet isotopique cinCtique secondaire du deuterium en a ainsi que la structure de l'ktat de transition de la rkaction SN2 du thiophCnolate de sodium avec le chlorure de n-butyle sont assez diffkrentes suivant qu'il s'agit d'une paire ionique complexe skparke par un solvant ou d'un ion libre. Dans les trois solvants oh il se produit des changements dans la forme des rkactifs ioniques, la paire ionique complexe conduit i un plus petit effet isotopique et i un Ctat de transition plus compact.[Traduit par la revue]

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Section: Proof Of An Ion Pair and Afree Ion Reactionmentioning

confidence: 99%

Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of S_N2 reactions

Westaway¹,

Lai²

1988

Can. J. Chem.

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“…For example, mild oxidation of alcohols to carbonyl compounds is a very important operation in organic synthesis. During a detailed study 7,8 of the primary and secondary kinetic isotope effects for E2 reactions, it was anticipated that the oxidation of substituted phenethyl alcohols (2) with the halosulphonamides 1 could shed light on the mechanism of oxidation of 2. Therefore, with the available data, it is important to report the detailed kinetic isotope effects for the oxidation of 2 by 1 in an aqueous homogeneous medium.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic studies of the oxidation of substituted phenethyl alcohols by N‐metallo‐N‐haloarylsulphonamides: kinetic isotope studies

Rangappa¹

2001

J of Physical Organic Chem

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The oxidation of para-substituted phenethyl alcohols (PEA, 2) by N-metallo-N-haloarylsulphonamides (1) in the presence of dilute HCl to the corresponding phenacetaldehydes (4) is first order with respect to oxidant (1) and [H ] and a fractional order each in [PEA] and [Cl À ]. Addition of the reaction product (3), ionic strength variations and variation of dielectric constant of the medium had no effect on the rate. The oxidation of PhCH 2 CD 2 OH (2) exhibited a substantial primary kinetic isotope effect (k H /k D = 5.83). The rates correlate satisfactorily with the Hammett free energy relationship. The activation parameters DH ≠ , DS ≠ , DG ≠ and logA were calculated for the reaction. The proposed mechanism is consistent with the observed results. RESULTS AND DISCUSSIONOxidation of 2 by 1 revealed that 1 mol of 1 was JOURNAL OF PHYSICAL ORGANIC CHEMISTRY

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“…In a recent study (1,2) on the E2 reaction of the 2-phenylethyl halides with tert-butoxide in tert-butyl alcohol it was found that the magnitude of the secondary a-deuterium kinetic isotope effect was dependent on the concentration of the abstracting base when chlorine and fluorine were the leaving groups. The secondary isotope effect, (kH/kD),, was inverse at "low" base concentrations and normal at "high" base concentrations.…”

Section: Introductionmentioning

confidence: 99%

Secondary α hydrogen–deuterium kinetic isotope effects in the syn-elimination reaction of 2-phenylethyldimethylamine oxide

Smith¹,

Westaway²

1987

Can. J. Chem.

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The secondary a-deuterium kinetic isotope effect has been measured for the thermal reaction of 2-phenylethyldimethylamine oxide in 90 mol% DMS0-+H20 at 60.OoC. A large secondary a-deuterium isotope effect of 1.158 per a-D was found, which indicates significant C-N bond rupture and very little double bond formation at the transition state for this concerted syn-elimination process. The observed large normal value for (kH/ kD), is discussed in terms of the use of secondary a-D isotope effects for the determination of stereochemistry for a concerted elimination process. Various isotope effects found for the syn elimination of the above amine oxide and those for the anti elimination of 2-arylethyltrimethylarnmonium salts with ethoxide are considered with respect to the relative transition state structures for syn-and anti-elimination reactions.PETER JAMES SMITH et KENNETH CHARLES WESTAWAY. Can. J. Chem. 65, 2149Chem. 65, (1987.Optrant a 60,OoC, dans un melange a 90 mol% de DMSO-H20, on a mesure l'effet isotopique cinttique secondaire du deuterium en a sur la rCaction thermique de l'oxyde de la phCnyl-2 Cthyl dimtthyl amine. On a observk un effet isotopique secondaire ClevC (1,158) pour le deuterium en a et ce resulta4 indique que, dans 1'Ctat de transition de cette Climination syn concertie, il se produit beaucoup de rupture de la liaison C-N et trks peu de formation de double liaison. On discute de cette valeur normale, mais ClevCe, qui a Ct C observte pour le (kH/ko), en fonction de I'utilisation des effets isotopiques secondaires des deutCrium en a pour la dttermination de la sttrtochimie d'un processus concert6 d'klimination. Divers effets isotopiques qui ont Ct C observCs pour 1'Climination syn de l'oxyde d'amine mentionnee plus haut et d'autres effets rapport& pour I'tlimination and des sels d'aryl-2 Cthyl trimethyl ammonium par 1'Cthylate ont Ct C considkrks en relation avec les structures relatives des Ctats de transition des reactions d'tliminations syn et anti.[Traduit par la revue] Introduction In a recent study (1,2) on the E2 reaction of the 2-phenylethyl halides with tert-butoxide in tert-butyl alcohol it was found that the magnitude of the secondary a-deuterium kinetic isotope effect was dependent on the concentration of the abstracting base when chlorine and fluorine were the leaving groups. The secondary isotope effect, (kH/kD),, was inverse at "low" base concentrations and normal at "high" base concentrations. These and other results were discussed in terms of both syn-and anti-elimination pathways promoted by various associated and dissociated base species. It was suggested that the (kH/kD)a effect may be useful as a criterion for determining the stereochemistry of E2 elimination reactions.At low tert-butoxide concentrations, it was suggested that the reaction of both the chloro and fluoro substrates proceed via a syn-elimination pathway where the loss of the leaving group and the P-hydrogen is assisted by the t-BuOK ion pair. For such a transition state, 1, which is expected to have considerabl...

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Large concentration effects on the magnitude of secondary alpha-deuterium kinetic isotope effects

Cited by 11 publications

References 12 publications

Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of S_N2 reactions

Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of S_N2 reactions

Mechanistic studies of the oxidation of substituted phenethyl alcohols by N‐metallo‐N‐haloarylsulphonamides: kinetic isotope studies

Secondary α hydrogen–deuterium kinetic isotope effects in the syn-elimination reaction of 2-phenylethyldimethylamine oxide

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Large concentration effects on the magnitude of secondary alpha-deuterium kinetic isotope effects

Cited by 11 publications

References 12 publications

Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of SN2 reactions

Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of SN2 reactions

Mechanistic studies of the oxidation of substituted phenethyl alcohols by N‐metallo‐N‐haloarylsulphonamides: kinetic isotope studies

Secondary α hydrogen–deuterium kinetic isotope effects in the syn-elimination reaction of 2-phenylethyldimethylamine oxide

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Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of S_N2 reactions

Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of S_N2 reactions