Mechanismen und Stereochemie der heterolytischen Fragmentierung

Grob, C. A.

doi:10.1002/ange.19690811502

Cited by 206 publications

(39 citation statements)

References 27 publications

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“…This reaction is known as Grob-type fragmentation. [10][11][12] This rearrangement is a symmetry-allowed process [12] and consequently it is thermodynamically favoured with respect to suspected bond-stretch isomerism leading to [2.2.2]propellane 1. Indeed, structure 3 is 44.4 kcal mol -1 lower in energy than [2.2.2]propellane 2.…”

Section: Resultsmentioning

confidence: 99%

“…(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) hypothesis that 1 should exhibit bond-stretch isomerism leading to the diradical 2, which might be jeopardized, however, by the Grob rearrangement [10][11][12] which yields 1,4-dimethylenecyclohexane (3). These predictions were essentially confirmed by Newton and Schulman [13] at a rather low level of theory according to present standards by using SCF/STO-3G calculations followed by two-configuration CI with very limited geometry optimization along the D 3h reaction coordinate for the bond-stretch isomerisation.…”

Section: Introductionmentioning

confidence: 99%

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[2.2.2]Propellane Isomerization by Grob Rearrangement: An Ab Initio MR‐AQCC Study

et al. 2007

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The multireference average quadratic couple cluster (MR-AQCC) method has been employed to explore isomerism in the [2.2.2]propellane 1 as well as the accompanying Grobtype fragmentation. It is shown that the open form 2 is more stable than the conventional closed propellane 1 by 3.6 kcal mol -1 . These two isomers are separated by a barrier as high as 22.7 kcal mol -1 , taking 1 as a reactant, a value that is in excellent agreement with experiment. However, system 2 is not a stable species because it is located in a very shallow energy minimum. Consequently, it undergoes almost barrierless cage-opening to the thermodynamically most stable

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

[2.2.2]Propellane Isomerization by Grob Rearrangement: An Ab Initio MR‐AQCC Study

et al. 2007

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“…The large accelerations were therefore ascribed to the frangomeric effect [8] of these substituents. As shown in the preceeding paper [5] y-substituents R exert similar polar effects in the solvolysis of acyclic tertiary chlorides 7.…”

Section: I)mentioning

confidence: 99%

Polar Effects in the Solvolysis of 4‐Substituted Bicyclo [2.2.2]octyl p‐Nitrobenzenesulfonates. Polar effects. VII

Grob

Rich

1979

Helvetica Chimica Acta

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SummaryHydrolysisofbicyclo[2.2.2]octylp-nitrobenzenesulfonate (14a,X =p-N02C6H4S03), and nineteen 4-R-substituted derivatives 14b-14 t in 70% aqueous dioxane yield the corresponding bicyclo [2.2.2]octanols 14 (X = OH), exclusively. The 7-center fragmentation to 1,4-dimethylidene-cyclohexane (15) is not observed. The logarithms of most of the rate constants, measured in 80% ethanol, correlate well with the corresponding inductive substituent constants a? of R. Hence, in these cases ionization rate is controlled by the inductive effect of R only. Poor correlations result when the substituents are potentially electrofugal groups, such as COO-, CH,OH, CH,NH,, CONH, and H, the deviations from the inductive regression line corresponding to rate enhancements of 1.6 to 8. These exalted substituent effects are tentatively ascribed to extended hyperconjugation involving two a-bonds. This study corroborates previous evidence that the inductive effect alone does not fully account for the polar effect of some substituents in reactions involving carbocations.In a recent paper in this series [l] a new experimental method for the determination of inductive substituent constants a? was introduced. This method, which is based on the measurement of the pK, of quinuclidinium perchlorate (1, R = H), and of numerous 4-substituted derivatives l), avoids the disadvantages inherent in previous ones [ 11.When applied to studies of substituent effects in nucleophilic substitution reactions a? values correlated well with the logarithms of observed rate constants for bimolecular substitution (SN2) [3] but not for some solvolysis reactions proceeding by way of carbeniumions [4] [5], as in the solvolysis of 1-R-substituted 3-bromoadamantanes (2a) in 80% ethanol. In fact, in the latter case three kinds of substituent effects were discerned: a) When R was hydrogen and alkyl or an electron-withdrawing (-I) substituent, such as BrCH,, COOH, Br or CN, the logarithms of the first order rate constants (logk) correlated very well with the respective 07 values. In these cases, then, ionization to adamantyl cations 3, the precursors of adamantanols 2b and ethyl ethers 2c, is controlled by the inductive effect of R alone; I)In a further paper these a? values are reexamined and revised where necessary [2].

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“…The bromoadamantanes l a were chosen for study because of the rigidly antiplanar orientation of the C (l), C (2)-and C (3), Br-bonds, which favors concerted fragmentation [5] and, by inference, also C, C-hyperconjugation. However, the question remained whether polar effects would be observable in similar, freely rotating acyclic models, such as 7.…”

Section: Discussionmentioning

confidence: 99%

Polar Substituent Effects in the Solvolysis of Acyclic Tertiary Chlorides Polar Effects VI

Grob

Waldner

1979

Helvetica Chimica Acta

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SummaryThe influence of twenty substituents R on the solvolysis rates and products of tertiary chlorides R-CH,CH2C(CH3),C1 (7) has been studied. H, CH3, (CH3),NCH2, ClCH,, C1, CN and NO2 exert an inductive effect only, as the good correlation of the rates with the corresponding inductive subslituent constants a? shows. Bulkier alkyl groups, i.e. isopropyl and t-butyl, lower the rate due to a Baker-Nathan effect, while the n-electron donors CH3S, CH30, HO and (CH3),N and the a-electron donors (CH3)3Sn and HOCH, cause rate increases based on CJ? constants. These accelerations are attributed to C , C-hyperconjugative and inductomeric effects which arise in the transition state for ionization. A comparison of the reactivity of the acyclic chlorides 7 and the corresponding 1-R-substituted 3-bromoadamantanes 1 a shows that polar substituent effects are more strongly transmitted in the rigid bicyclic compounds l a than in the flexible acyclic compounds 7.Introduction. As recently reported [ 13 several kinds of polar substituent effects are observable in the solvolysis of 1-R-substituted 3-bromoadam antanes l a in 80% (v01.-%) ethanol. When R was a hydrogen atom, an alkyl or an electron withdrawing substituent such as BrCH,, HOOC, Br or CN, the logarithms of the

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Mechanismen und Stereochemie der heterolytischen Fragmentierung

Cited by 206 publications

References 27 publications

[2.2.2]Propellane Isomerization by Grob Rearrangement: An Ab Initio MR‐AQCC Study

[2.2.2]Propellane Isomerization by Grob Rearrangement: An Ab Initio MR‐AQCC Study

Polar Effects in the Solvolysis of 4‐Substituted Bicyclo [2.2.2]octyl p‐Nitrobenzenesulfonates. Polar effects. VII

Polar Substituent Effects in the Solvolysis of Acyclic Tertiary Chlorides Polar Effects VI

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