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Volumn 73, Issue 22, 2008, Pages 8921-8928

Choice of bond dissociation enthalpies on which to base the stabilization energies of simple radicals: DH(R-H) is preferred because DH(R-Me) and DH(R-R) are perturbed by changes in chain branching

Author keywords

[No Author keywords available]

Indexed keywords

CHEMICAL BONDS; DISSOCIATION; ENTHALPY; HYDROCARBONS; PARAFFINS; STABILIZATION; THERMOCHEMISTRY;

EID: 56449122060     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo801529y     Document Type: Article
Times cited : (17)

References (68)
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    • H values herein, and the derived DH(R-X) values, are for the gaseous standard state at 298 K
    • are listed in the Supporting Information
    • fH values herein, and the derived DH(R-X) values, are for the gaseous standard state at 298 K. The "compromise" values chosen for alkanes and alkyl radicals (refs 2-14) are listed in the Supporting Information.
    • The compromise , pp. 2-14
    • ΔARTINFSTARTfARTINFEND, A.1
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    • Gronert, S. J. Org. Chem. 2006, 71, 1209 (correction p 9560).
    • (a) Gronert, S. J. Org. Chem. 2006, 71, 1209 (correction p 9560).
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    • Martinho Simoes, J. A, Greenberg, A, Liebman, J. F, Eds, Blackie Academic and Professional: London
    • Tsang, W. In Energetics of Organic Free Radicals; Martinho Simoes, J. A.; Greenberg, A.; Liebman, J. F., Eds.; Blackie Academic and Professional: London, 1996.
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    • for additional discussion of the use of empirical models and the ambiguities in definitions and reference states for hyperconjugation and geminal interactions; this model however does not treat radicals. See
    • (c) See Zavitsas, A. A.; Matsunaga, N.; Rogers, D. W. J. Phys. Chem A 2008, 112, 5734. for additional discussion of the use of empirical models and the ambiguities in definitions and reference states for hyperconjugation and geminal interactions; this model however does not treat radicals.
    • (2008) J. Phys. Chem A , vol.112 , pp. 5734
    • Zavitsas, A.A.1    Matsunaga, N.2    Rogers, D.W.3
  • 31
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    • For a similar tabular summary, see ref 12
    • For a similar tabular summary, see ref 12.
  • 37
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    • Note that this assumption is not consistent with the importance of 1,3-interactions implicit in the other models (refs 6 and 7) considered herein
    • Note that this assumption is not consistent with the importance of 1,3-interactions implicit in the other models (refs 6 and 7) considered herein.
  • 38
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    • These values have been adjusted slightly based on the DH values used herein, as shown in the Supporting Information
    • These values have been adjusted slightly based on the DH values used herein, as shown in the Supporting Information.
  • 39
    • 56449088356 scopus 로고    scopus 로고
    • Although such values are of course often derived from eq 1, the use of experimental values of ΔfH(R-X) and Δ fH(X•) in the calculation should avoid the complications from varying X demonstrated in Table 1 see ref 9
    • fH(X•) in the calculation should avoid the complications from varying X demonstrated in Table 1 (see ref 9).
  • 40
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    • We consider herein only enthalpic differences, not free-energy differences
    • We consider herein only enthalpic differences, not free-energy differences.
  • 41
  • 43
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    • Reference 4
    • (c) Reference 4.
  • 45
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    • Although the ΔfH values used herein (Table S-1, Supporting Information) are slightly different that those used by Wodrich and Schleyer, we have not attempted to adjust their Hi parameters
    • i parameters.
  • 46
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    • Protobranching is defined in ref 6b as the net stabilizing 1,3-alkyl-alkyl interactions (the net attractive composite of carbon and hydrogen interactions) existing in normal, branched, and most cycloalkanes but not in methane and ethane. [It] is a net favorable composite of attractions (larger) and repulsions (smaller).
    • Protobranching is defined in ref 6b as "the net stabilizing 1,3-alkyl-alkyl interactions (the net attractive composite of carbon and hydrogen interactions) existing in normal, branched, and most cycloalkanes but not in methane and ethane. [It] is a net favorable composite of attractions (larger) and repulsions (smaller)."
  • 48
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    • A correction of -0.8 kcal/mol was applied to account for its obligatory 1,4 gauche interaction that is not addressed in the model
    • A correction of -0.8 kcal/mol was applied to account for its obligatory 1,4 gauche interaction that is not addressed in the model.
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    • Although both simplified models treat the methyl (or alkyl) group involved in a 1,3-interaction as a hard-sphere, the interactions are of course composites among more than one non-bonded atom pair. To illustrate, consider some interatomic distances about the central carbon in the MM3-minimized (ref 36) staggered structure for propane. While the closest 1,3 H-H interaction is simply between two hydrogen atoms at 1.79 Å well within their combined van der Waal's radii of 2.4 Å, the 1,3 Me-H interaction features two 1,3 H-C interactions at 2.18 Å, and the 1,3 Me-Me interaction features a 1,3 C-C interaction at 2.55 Å, two 1,4 C-H interactions at 2.83 Å, and two 1,5 H-H interactions at 2.65 Å
    • Although both simplified models treat the methyl (or alkyl) group involved in a 1,3-interaction as a "hard-sphere," the interactions are of course composites among more than one non-bonded atom pair. To illustrate, consider some interatomic distances about the central carbon in the MM3-minimized (ref 36) staggered structure for propane. While the closest 1,3 H-H interaction is simply between two hydrogen atoms at 1.79 Å (well within their combined van der Waal's radii of 2.4 Å), the 1,3 Me-H interaction features two 1,3 H-C interactions at 2.18 Å, and the 1,3 Me-Me interaction features a 1,3 C-C interaction at 2.55 Å, two 1,4 C-H interactions at 2.83 Å, and two 1,5 H-H interactions at 2.65 Å.
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    • 4CH which we do not consider herein.
    • 4CH which we do not consider herein.
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    • C.
    • C.
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    • "LINEST" function in Microsoft Excel with b = 0. The presence of a collinearity is signaled by a 0.00 ± 0.00 output for one of the parameters.
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    • For the latter two pairs there is an ambiguity whether the terminal or internal olefin is the precursor state. We illustrate the former, but the trends are the same for the latter, although of course the values of ΔH differ by the differences of ΔfH of the olefins; cf. ref 13
    • fH of the olefins; cf. ref 13.
  • 67
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    • Although we do not explicitly show the details for the corresponding differences for propargylic radicals because the thermochemical data base is less sure, the analogous differences for propargyl, 1-methylpropargyl, and 1,1-dimethylpropargyl are similar: 2.5, 4.7, and 4.9 kcal/mol
    • Although we do not explicitly show the details for the corresponding differences for propargylic radicals because the thermochemical data base is less sure, the analogous differences for propargyl, 1-methylpropargyl, and 1,1-dimethylpropargyl are similar: 2.5, 4.7, and 4.9 kcal/mol.
  • 68
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    • fH value for ethynyl is controversial; we accept the recent revised value from ref 14, see Table S-1, Supporting Information.
    • fH value for ethynyl is controversial; we accept the recent revised value from ref 14, see Table S-1, Supporting Information.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.