Thermochemistry of the orthogonal butadienes (Z,Z)-3,4-dimethylhexa-2,4-diene and 2,3-di-tert-butylbuta-1,3-diene

Roth, Wolfgang R.; Lennartz, Hans Werner; Doering, W. von E.; Dolbier, William R.; Schmidhauser, John C.

doi:10.1021/ja00214a036

Cited by 32 publications

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“…Steric factors need to be considered in the interaction of phenyl with the carbon−carbon double bond beyond that in styrene itself and trans -β-substituted styrenes, in which they are assumed to be negligible by definition. These factors are less important in butadienes, for example, where special constitutional perturbations are required to enforce a significant departure from coplanarity. − But in styrenes, a cis orientation of β-substituents, the presence of substituents in the α-position or in the ortho positions of the phenyl ring, can be expected sterically to cause deviations from the coplanar conformation optimum for π-electron delocalization.…”

Section: Background To Conjugative Interactionmentioning

confidence: 99%

Conjugative Interaction in Styrenes

et al. 1997

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Conjugative interactions of the carbon−carbon double bond are fundamental in organic chemistry. In this work, equilibria are established among conjugated and unconjugated isomers of two β-substituted styrenes, 1-phenylbut-1-ene and 1-phenyl-3-methylbut-1-ene, and one α,β-disubstituted styrene, 2-phenyl-5-methylhex-2-ene, over a range of temperatures (the van't Hoff method) in hexamethylphosphoric triamide and potassium tert-butoxide. From the trans styrenes of the first two sets, an enthalpy of conjugative interaction of phenyl vis-à-vis alkyl (ΔΔH ConjInter/Alk) = −2.5 ± 0.2 kcal/mol [−5.1 kcal/mol defined as phenyl vis-à-vis hydrogen (ΔΔH ConjInter/H)] is observed, while the cis styrenes reveal an attenuated ΔΔH ConjInter/Alk of −1.1 kcal/mol (ΔΔH ConjInter/H = −2.7 kcal/mol). The α-methyl group in the third set also leads to a reduced conjugative interaction. Entropy plays an important role in determining positions of equilibrium. Free energies of conjugation are reported for several sterically hindered o-methyl-substituted styrenes.

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Section: Background To Conjugative Interactionmentioning

confidence: 99%

Conjugative Interaction in Styrenes

et al. 1997

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“…Experimental data are given in Table 3. The heats of hydrogenation have not been corrected experimentally for differences in enthalpies of solution of educts and products, because for saturated hydrocarbons such differences are 0.1 kcall mol in isooctane [17]. Differences in enthalpies of vaporization between educts and Calculated from k for 8-OTs by multiplying by 28.5. products were calculated on the basis of Kavats indices, which, in a series of structurally related substances, are linearly related to boiling points and, therefore, to heats of vaporization [17].…”

Section: ')mentioning

confidence: 99%

Norbornanes. Part 21. Bridging strain in norbornyl and oxanorbornyl cations

Flury

Grob

Wang

et al. 1988

Helvetica Chimica Acta

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(1 1. V. 88)Further evidence is presented that the 2-norbomyl cation is stabilized primarily by C(2)-C{6) bridging, and that C(2)-C(7) bridging leads to prohibitive strain. Thus, a comparison of the heats of hydrogenation of nortricyclene 17 and bicycl0[3.2.0.0~.~]heptane 18 indicates that the strain energy of the latter is ca. 21.5 kcal/mol higher than that of 17. Furthermore, 6-exo-2-oxabicyclo[2.2. ljheptyl sulfonates 8 ionize with strong O(2) participation to the bridged oxonium ion 12. In contrast, 2-endo-7-oxabicyclo[2.2.1]heptyl sulfonates 11 ionize without O(7) participation to form the unbridged carbenium ion 15.As pointed out in [la], displacement (&2) reactions of bi-and tricyclic halides and sulfonates with nucleophilic solvents are sterically hindered, if the nucleofuge is adjacent to a bridgehead atom. In these cases, solvolysis reactions occur via carbenium ions (&1) and tend to be slow unless assisted by bridging of the cationic center by neighboring atoms.In carbocyclic compounds, bridging involves weak bonding between the electrophilic cationic center and neighboring C-atoms, thereby generating some of the strain associated with the subdivision of cyclic structures into smaller rings [2]. Differential bridging of neighboring C-atoms, therefore, accounts for the frequently different rates and products of epimeric bi-and tricyclic sulfonates [lb], such as the exo-and endo-2-norbornyl p -bromobenzenesulfonates (brosylates) and p -toluenesulfonates (tosylates) 1 (X = BsO) and 2 (X = TsO), respectively, which differ by factors of more than 3002).In their original communications [3], Winstein and Trifan attributed the higher rate of 1-OBs to anchimeric assistance of exo-ionization by the antiperiplanar C( 1)-C(6) bonding electrons, i.e. by so-called CT participation3), which is absent in the endo-epimer 2-OBs. According to a modified version of this rationale [6], the transition state for exo-ionization is stabilized by C,C hyperconjugation with the strained and antiperiplanar C( 1)-C(6) CT bond. Thus, both interpretations stress the role of the C( 1)-C(6) bonding electrons in controlling the relative rates of I-OBs and 2-OBs. On the other hand, the role of the equally strained C( 1)-C(7) bond, which is somewhat deflected from the plane ') 2, 3,The IUPAC name for norbornane: 8,9,1U-trinorbornane. The rate ratio at 25"is 350 in AcOH [3], 580 in 80% EtOH [lb], and cn. 2000 in H2O [4].For a definition of u participation, see [5].

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“…The values are not corrected for evaporation effects, but for effects of the solvent according to the literature. [16] The hydrogen uptake was used for the analyses.…”

Section: Introductionmentioning

confidence: 99%

Thermochemistry of 7,7-Difluoro-2,7-toluenediyl

Roth¹,

Figge²

2000

Eur. J. Org. Chem.

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From the oxygen and temperature dependence of the trapping rate of 7,7‐difluorobenzocyclopropene (1) in the range 180−240 °C, the energy profile of the equilibrium 1 →←2 has been obtained. From the heat of hydrogenation of 1, its heat of formation is derived (ΔH of = +3.8 kcal·mol−1), as a result of which the heat of formation of the singlet state of the diradical 2 is estimated as 25.7 kcal·mol−1. Whereas the trapping experiments demonstrate unambiguously a triplet ground state for 2, only a lower limit for the singlet‐triplet splitting (> 6 kcal·mol−1) can be given.

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Thermochemistry of the orthogonal butadienes (Z,Z)-3,4-dimethylhexa-2,4-diene and 2,3-di-tert-butylbuta-1,3-diene

Cited by 32 publications

References 0 publications

Conjugative Interaction in Styrenes

Conjugative Interaction in Styrenes

Norbornanes. Part 21. Bridging strain in norbornyl and oxanorbornyl cations

Thermochemistry of 7,7-Difluoro-2,7-toluenediyl

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