Use of kinetic isotope effects in mechanism studies. 4. Chlorine isotope effects associated with alkoxide-promoted dehydrochlorination reactions

Koch, H.; McLennan, Duncan J.; Koch, Judith G.; Tumas, William; Dobson, B.; Koch, Nanci H.

doi:10.1021/ja00345a043

Cited by 22 publications

(22 citation statements)

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“…[2]. As calculated by repetitive sample/reference comparisons on a single gas sample, 6 values were as constant as those previously reported from our laboratory, and varied by no more than 0.5% (19,20). However, day-to-day variations in S for the same sample of methyl chloride were of the order of +2-3%, when compared with the same reference gas.…”

Section: Resultssupporting

confidence: 71%

“…The first line of Table 4 shows the dependence of k35/k37 on nl as the TS structure is changed from reactant-like to product-like in a case where (i) the choice of parameters for formulation of f12 keeps v?, the reaction coordinate frequencies, at low absolute values and (ii) only weak hydrogen bonding of the chlorine is similated. The k35/k37 values are seen to increase as the TS C ,.... Cl bond is made weaker, as expected (20,22,26,27).…”

Section: Model Calculations Of Chlorine Isotope Effectssupporting

confidence: 69%

“…Both p+ (3) and Grunwald-Winstein m values (23) are numerically large for the 1-phenylethyl halide solvolysis system, suggesting that bond rupture and charge transfer are well advanced at the TS. Theory decrees that if simple carbon-chlorine stretching comprises the reaction coordinate the TS should become more reactant-like as electrondonating groups stabilize the carbocationic portion of the ion pair (24,25) and if such a variation is significant the chlorine isotope effect should become smaller (20,26,27). It does not .'…”

Section: Transition State Variationmentioning

confidence: 99%

“…Chlorine isotope effects in the solvolysis of tert-butyl chloride (12) and substituted benzyl chlorides (13), and sulfur isotope effects in the solvolysis of the tert-butyldimethylsulfonium (14) and benzyldimethylsulfonium (15) cations appear to be the only available examples. In view of our interests in the reactions of 1-phenylethyl derivatives (1 6-18), in chlorine isotope effects (19,20), and in isotope effects in general solvolytic processes (21,22), we decided to measure chlorine isotope effects in the solvolysis of ring-substituted 1-phenylethyl chlorides.…”

Section: Introductionmentioning

confidence: 99%

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Chlorine isotope effects in the solvolysis of substituted 1-phenylethyl chlorides

McLennan¹,

Stein²,

Dobson³

1986

Can. J. Chem.

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Kinetic chlorine isotope effects attending the solvolysis of several ring-substituted 1-phenylethyl chlorides in alcohol-water solvent mixtures are reported. The k35/k37 values are insensitive to the identity of ring substituents and to solvent composition. Results are interpreted in terms of an SN1 heterolytic process incorporating a significant amount of internal return. Theoretical calculations suggest that the incipient chloride ion in the transition state may be strongly hydrogen-bonded. On a mesurt les effets isotopiques cinttiques du chlore qui accompagnent les solvolyses de plusieurs chlorures de phtnyl-1 Cthyle substituts sur le cycle. Les valeurs de k35/k37 sont insensibles h la nature des substituants sur le cycle ainsi qu'h la composition du solvant. On interprbte les rtsultats en fonction d'un processus htttrolytique SN1 incorporant une part importante de retour interne. Des calcultes thkoriques suggbrent que I'ion chlorure qui attaque dans l'ttat de transition pourrait Ctre fortement lit par des liaisons hydrogbnes.[Traduit par la revue]

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Section: Resultssupporting

confidence: 71%

Section: Model Calculations Of Chlorine Isotope Effectssupporting

confidence: 69%

Section: Transition State Variationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Chlorine isotope effects in the solvolysis of substituted 1-phenylethyl chlorides

McLennan¹,

Stein²,

Dobson³

1986

Can. J. Chem.

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“…It is-ienerilly considered that the reaction of the 2-phenylethyl halides with ethoxide in ethanol proceeds by way of the E2 mechanism (I3, [26][27][28][29] …”

Section: T-buohmentioning

confidence: 99%

Secondary α-deuterium kinetic isotope effects for the E2 reaction of the 2-phenylethyl halides with tert-butoxide ion in tert-butyl alcohol

Smith¹,

Rangappa²,

Westaway³

1985

Can. J. Chem.

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PETER JAMES SMITH, KANCHUGARAKOPPAL S. RANGAPPA, and KENNETH CHARLES WESTAWAY. Can. J. Chem. 63, 100 (1985).Secondary a-deuterium kinetic isotope effects have been determined for the elimination reactions of 2-phenylethyl halides with tert-butoxide in tert-butyl alcohol at 40°C in the presence and absence of the crown ether 18C6. The second-order rate constant k, and the normal (kt'/kD), effect remained constant when the tert-butoxide concentration was varied for reaction of the iodo and bromo compounds. However, both the magnitude of k, and the secondary a-deuterium isotope effect were significantly dependent on [t-BuO-] when chlorine and fluorine are the leaving groups. It is noteworthy that (kH/k"),, is inverse for the reaction of both the chloro and fluoro compounds at "low" base concentrations and normal at "high" base concentrations. These results are discussed in terms of both syn-and anti-elimination pathways promoted by various associated and dissociated base species. It is suggested that the (kH/k"),, effect may be useful as a criterion for determining the stereochemistry of E2 elimination reactions.PETER JAMES SMITH, KANCHUGARAKOPPAL S. RANGAPPA et KENNETH CHARLES WESTAWAY. Can. J . Chem. 63, 100 (1985). Operant 3 40°C et en prtsence ou en I'absence de I'tther couronne 18C6, on a dttermink les effets isotopiques cinttiques secondaires des deuterium en a sur les reactions d'klimination des halogtnures de phenyl-2 Cthyles par la tert-butylate dans I'alcool tert-butylique. Dans les cas des compos6s iodCs ou bromCs, la constante de vitesse du deuxikme ordre (kZ) ainsi que I'effet normal (kH/k"),, demeurent constants lorsqu'on fait varier la concentration du tert-butylate. Toutefois, lorsque les groupes nucltofuges sont soit Ie fluor ou le chlore, ['amplitude de k2 ainsi que I'effet isotopique secondaire des deuterium en a varient d'une f a~o n importante avec la concentration de I'ion tert-butylate. I1 est notable que, pour les rkactions des composts fluorCs ou chlorCs 3 de "basses" concentrations de base, la valeur (kl'/k"),, est inverse; toutefois, h des concentrations "ClevCes" de base, cette valeur est normale. On discute de ces resultats en fonction de voies d'eliminations syn et anti qui sont PavorisCes par diverses cspkces basiques associCcs et dissocites. On suggkre que I'effet (kk'/k"),, pourrait etre un critkrc utile pour dCterminer la sttrtochimie des rCactions dlCliminations E2.[Traduit par le journal]The elimination reaction of the 2-arylethyl derivatives with different leaving groups Y, ArCH,CH,Y, has been extensively studied (1 -6) under a variety of solvent/base conditions. It has been established that the majority of the reactions proceed by way of the E2 mechanism following the anti pathway (5,7). Experimental studies (8)(9)(10)(11)(12)(13)(14) have demonstrated that the structures of the respective E2 transition states vary significantly in accord with theoretical re dictions (15)(16)(17)(18)(19)(20).The reaction of the 2-arylethyl quaternary ammonium ions with base has been-shown to h...

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ChemInform Abstract: USE OF KINETIC ISOTOPE EFFECTS IN MECHANISM STUDIES. 4. CHLORINE ISOTOPE EFFECTS ASSOCIATED WITH ALKOXIDE‐PROMOTED DEHYDROCHLORINATION REACTIONS

Koch

McLennan

Koch

et al. 1983

Chemischer Informationsdienst

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Use of kinetic isotope effects in mechanism studies. 4. Chlorine isotope effects associated with alkoxide-promoted dehydrochlorination reactions

Cited by 22 publications

References 2 publications

Chlorine isotope effects in the solvolysis of substituted 1-phenylethyl chlorides

Chlorine isotope effects in the solvolysis of substituted 1-phenylethyl chlorides

Secondary α-deuterium kinetic isotope effects for the E2 reaction of the 2-phenylethyl halides with tert-butoxide ion in tert-butyl alcohol

ChemInform Abstract: USE OF KINETIC ISOTOPE EFFECTS IN MECHANISM STUDIES. 4. CHLORINE ISOTOPE EFFECTS ASSOCIATED WITH ALKOXIDE‐PROMOTED DEHYDROCHLORINATION REACTIONS

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