Stereochemistry of allylic rearrangements. 16. Ion-pair return associated with solvolysis of exo- and endo-bicyclo[3.2.1]oct-3-en-2-yl p-nitrobenzoate in aqueous acetone

Goering, Harlan L.; Anderson, Raymond P.

doi:10.1021/ja00488a034

Cited by 8 publications

(7 citation statements)

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“…As described above, the kinetic analysis indicates that the rate ratio k - 2 / k 3 for internal return relative to solvent capture for the ion pair 18 is 7.7, even in the highly nucleophilic solvent CD 3 CO 2 D. This is rather larger than values that have been obtained for other allylic systems, for example, a value of 2.1 in 90/10 acetone/H 2 O found using 18 O equilibration 8a. The value of 7.7 is remarkable since this is a relatively unhindered substrate that should be rather accessible for backside solvent attack.…”

Section: Discussionmentioning

confidence: 74%

“…For comparison, in one previous study 8d of an allylic rearrangement of a p -nitrobenzoate ester 18 O equilibration to the extent of 90−100% was observed, while for 2-pent-3-enyl p -nitrobenzoate there was a preference for bonding of the carbonyl oxygen during the symmetrical allylic rearrangement 8e by a factor of 3.8 to 4.9. Preferential return of an original tertiary carbon bonded oxygen to a secondary carbon following Wagner−Meerwein rearrangement to the extent of 6.1:1 in an 18 O-labeled hexafluorobutyrate ester has also been observed 8f…”

Section: Discussionmentioning

confidence: 88%

“…These results are consistent with the solvolysis of 15 proceeding to an ion pair 18 that can partition between return to the rearranged tosylate 16 and solvent capture to form 17 , but without return to the less stable starting tosylate 15 (eq 5). There have been numerous previous demonstrations of return in allylic systems,8ab but the conversion of 15 to 16 is unusual in that there is an isomerization of a tertiary to a secondary substrate.…”

Section: Discussionmentioning

confidence: 99%

“…The alternative mechanism of formation of the rearranged tosylate 16 without ionization but by a sigmatropic rearrangement of 15 appears highly unlikely, as the strong dependence of the reaction rate on solvent polarity, and the significant normal salt effect, indicate a very polar transition state, and such pathways have not been demonstrated in other allylic rearrangements …”

Section: Discussionmentioning

confidence: 99%

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3-(Trifluoromethyl)indenyl Cation: Ion Pair Return in the Formation of an Antiaromatic and Electron-Deficient Doubly Destabilized Carbocation

et al. 1997

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The solvolysis of 3-(trifluoromethyl)-3-indenyl tosylate (15) occurs with extensive isomerization to 1-(trifluoromethyl)-3-indenyl tosylate (16), which reacts in a slower process to give the substitution product 17. Kinetic analysis of a model involving an intermediate allyl cation/tosylate ion pair 18 gave a partitioning ratio in CD(3)CO(2)D at 99.6 degrees C for 18 of 7.7 for return with allylic rearrangement compared with solvent capture. Studies of 15 with specific (18)O labeling show no scrambling in recovered 15 and partial scrambling in rearrangement to 16. The m value measuring the dependence of the reactivity of 15 on the solvent-ionizing parameter Y(OTs) is 0.78, which is significantly less than that of 1.23 for the analogous 9-(trifluoromethyl)-9-fluorenyl tosylate 7. Normal salt effects in CF(3)CO(2)H predominate for 15, and the special salt effect involves no more than 14% capture of solvent-separated ion pairs by 0.551 M KO(2)CCF(3). The substrate 15 has a net diminution in reactivity of more than 10(9) relative to the secondary indanyl tosylate 22, with factors of 10(6) and 10(3) attributable to antiaromaticity and to the electron-withdrawing CF(3) group, respectively. The solvolysis of 15 is proposed to occur by formation of an ion pair with significant nucleophilic solvation at the relatively unhindered allylic carbon, but internal return occurs in preference to solvent or salt capture. Solvolysis of the rearranged tosylate 16 occurs with a strong rate retardation by the gamma-CF(3) group, a large extent of internal return, and with a normal salt effect.

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Section: Discussionmentioning

confidence: 74%

Section: Discussionmentioning

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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3-(Trifluoromethyl)indenyl Cation: Ion Pair Return in the Formation of an Antiaromatic and Electron-Deficient Doubly Destabilized Carbocation

et al. 1997

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“…Hughes et al (3) followed radio-iodide exchange with 2-iodooctane, and radio-bromide exchanges with 1-bromo-1-phenylethane and 2-bromopropanoic acid in the mid1930s. Others have also used radio tracers to follow exchanges (4)(5)(6)(7)(8)(9). We employed the electrodeposition of silver halide at a silver anode, a method developed and extensively used by Beronius (3, to follow radio-halide exchanges (6,7).…”

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confidence: 99%

β-Deuterium kinetic isotope effects for identity processes: bromide ion substitution at 1-bromo-1-arylethanes and 2-bromooctane

Stein¹

1994

Can. J. Chem.

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. While deuterium kinetic isotope effects for solvolyses have been extensively studied, other nucleophilic substitutions have received less attention, and identity processes, that is, substitutions where the nucleophile and leaving group are the same, have rarely been examined. Identity reactions must pass through a truly symmetrical stage, a transition state or an intermediate, so that data will be of interest to both theoretical and experimental chemists. Values of kHlkD have been determined by polarimetry for bromide exchange-racemization at ArCHBrCH3/CD3 (Ar = C6H5, 4-Br-and 4-Me-C6H4, and 3,4,-dimethyl-C6H3) in acetone, acetonitrile, and nitromethane. Observed values are analogous to values seen in solvolyses. They range from 1.01 to 1.35 and, in some cases, increase markedly as the concentration of Bu4NBr decreases. Solvolyses are either first order or pseudo first order whereas plotting observed racemization rate versus [Bu4NBr] allows separation of first-and second-order components; those species giving more stable carbocations in the more dipolar solvents, the systems showing kHlkD variation with Br-concentration, alone show an appreciable first-order component. The second-order kHlkD ratio averages 1.062 2 4 . 0 1 8 at temperatures ranging from 25 to 50°C for all substrates in the three solvents, very analogous to the values seen for racemization of 1,1,1 -d3-2-bromooctane or solvolysis of ethyl substrates but considerably lower than the typical solvolysis values of 1.15-1.25 for secondary, and 1.35-1.5 for tertiary substrates. The first-order kHlkD values obtained are higher, 1.1-1.5. These and other results are discussed. de Bu4NBr. Les solvolyses sont soit du premier ordre ou du pseudo premier ordre alors que, dans notre cas, la courbe de la rackmisation en fonction de la concentration de Bu4NBr permet de sCparer les composantes du premier et du deuxieme ordre; seules les especes conduisant B carbocations les plus stables dans les solvants les plus dipolaires, les systemes presentant une variation du kH/kD en fonction de la concentration du Br-, prksentent une portion importante des rCaction du premier ordre. Pour tous les substrats, dans les trois solvants, ides temptratures allant de 25 a 50°C, le valeur du rapport kH/kD des rkactions du deuxikme ordre rend une moyenne de 1,062 5 0,018 et elles sont tres semblables ? I celles observkes lors de la ractmisation du I ,1,1-d3-2-bromoCthane ou de la solvolyse des substrats avec des groupes Cthyles; elles sont toutefois beaucoup plus basses que les valeurs typiques de 1,15 1,25 ou 1,35 B 1,5 obsewtes lors de solvolyses de substrats secondaires ou tertiaires. Les valeurs des kH/kD du premier ordre sont plus ClevCes (1,l-1,5). On discute de ces valeurs et d'autres rtsultats.[Traduit par la redaction]

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ChemInform Abstract: STEREOCHEMISTRY OF ALLYLIC REARRANGEMENTS. 16. ION‐PAIR RETURN ASSOCIATED WITH SOLVOLYSIS OF EXO‐ AND ENDO‐BICYCLO(3.2.1)OCT‐3‐EN‐2‐YL P‐NITROBENZOATE IN AQUEOUS ACETONE

Goering¹,

Anderson²

1979

Chemischer Informationsdienst

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Stereochemistry of allylic rearrangements. 16. Ion-pair return associated with solvolysis of exo- and endo-bicyclo[3.2.1]oct-3-en-2-yl p-nitrobenzoate in aqueous acetone

Cited by 8 publications

References 2 publications

3-(Trifluoromethyl)indenyl Cation: Ion Pair Return in the Formation of an Antiaromatic and Electron-Deficient Doubly Destabilized Carbocation

3-(Trifluoromethyl)indenyl Cation: Ion Pair Return in the Formation of an Antiaromatic and Electron-Deficient Doubly Destabilized Carbocation

β-Deuterium kinetic isotope effects for identity processes: bromide ion substitution at 1-bromo-1-arylethanes and 2-bromooctane

ChemInform Abstract: STEREOCHEMISTRY OF ALLYLIC REARRANGEMENTS. 16. ION‐PAIR RETURN ASSOCIATED WITH SOLVOLYSIS OF EXO‐ AND ENDO‐BICYCLO(3.2.1)OCT‐3‐EN‐2‐YL P‐NITROBENZOATE IN AQUEOUS ACETONE

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