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Volumn 61, Issue 6, 1996, Pages 2027-2030

Absolute rate constants for radical additions to alkenes in solution. The synergistic effect of perfluorination on the reactivities of n-alkyl radicals

Author keywords

[No Author keywords available]

Indexed keywords

ALKYL RADICALS; FREON 113; LASER FLASH PHOTOLYSIS; PERFLUORINATION; RADICAL ADDITION; SYNERGISTIC EFFECT;

EID: 0000863207     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo951782v     Document Type: Article
Times cited : (34)

References (45)
  • 3
    • 0026000469 scopus 로고    scopus 로고
    • For α,α-difluoro-n-alkyl radical cyclizations see, e.g., Cavicchio, G.; Marchetti, V.; Arnone, A.; Bravo, P.; Viani, F. Tetrahedron 1991, 47, 9439-9448
    • (a) For α,α-difluoro-n-alkyl radical cyclizations see, e.g., Cavicchio, G.; Marchetti, V.; Arnone, A.; Bravo, P.; Viani, F. Tetrahedron 1991, 47, 9439-9448
  • 5
    • 0026649490 scopus 로고    scopus 로고
    • For β,β-difluoro-n-alkyl radical cyclizations see, e.g., Morikawa, T.; Kodama, Y.; Uchida, J.; Takano, M.; Washio, Y.; Taguchi, T. Tetrahedron 1992, 48, 8915-8926.
    • (b) For β,β-difluoro-n-alkyl radical cyclizations see, e.g., Morikawa, T.; Kodama, Y.; Uchida, J.; Takano, M.; Washio, Y.; Taguchi, T. Tetrahedron 1992, 48, 8915-8926.
  • 6
    • 76049093553 scopus 로고    scopus 로고
    • The modified (see footnote b to Table 1) rate constant for addition of a non-fluorinated n-alkyl radical to α-methylstyrene is probably about a factor of 5 lower than the true value. Certainly, it seems very improbable that addition to this substrate could be slower than addition to styrene.
    • The "modified" (see footnote b to Table 1) rate constant for addition of a non-fluorinated n-alkyl radical to α-methylstyrene is probably about a factor of 5 lower than the true value. Certainly, it seems very improbable that addition to this substrate could be slower than addition to styrene.
  • 7
    • 76049089403 scopus 로고    scopus 로고
    • This extension of the α-fluoroalkyl radical series can be justified by the fact that CH2F• and CHF2F• have reactivities roughly comparable to those of RCH2CH 2CHFF• and RCH2CH2CF2F•, respectively.8
    • 8
  • 8
    • 76049119180 scopus 로고    scopus 로고
    • For example, in acetonitrile kadd (CH 2FF•, C6F5CH=CH2, 0.35 ± 0.04) × 106 M-1 s-1, kadd (CHF2F•, C6H 5CH=CH2, 4.1 ± 0.4) × 106 M-1 s-1 and kadd (CHF2F•, C6F5CH=CH2, 5.5 ± 0.7) × 106 M-1 s-1 cf, Table 1
    • -1 (cf., Table 1).
  • 9
    • 76049126145 scopus 로고    scopus 로고
    • Fischer, H. In Magnetic Properties of Free Radicals; Landolt-Börnstein, New Series; Fischer, H., Hellwege, K.-H., Eds.; Springer-Verlag: Berlin, 1977; 9, Part b, Chapter 3.
    • Fischer, H. In Magnetic Properties of Free Radicals; Landolt-Börnstein, New Series; Fischer, H., Hellwege, K.-H., Eds.; Springer-Verlag: Berlin, 1977; Vol. 9, Part b, Chapter 3.
  • 10
    • 76049091870 scopus 로고    scopus 로고
    • E.g.,9 CH3CH2•, a (2Hα, 22.2 G, a (13Cα), 39.1 G, g, 2.0026; CH 3CH2CH2bull;, a (2Hα, 22.1 G, g, 2.0026; CF3CH2•, a (2Hα, 23.8 G, g) 2.0023; CF3CF2CH2•, a 2Hα, 22 G
    • 2•, a (2Hα) = -22 G.
  • 11
    • 76049124396 scopus 로고    scopus 로고
    • E.g.,9 RCH2CH2•;10 CH2F•, a (2Hα, 21.1 G, a (Fα), 64.3 G, a (13Cα, 54.8 G, g, 2.0045; CF 3OCH2CHF•, a (Hα, 21.4 G, a (Fα, 63.5 G; CHF2•, a (Hα, 22.2 G, a (2Fα, 84.2 G, a (13Cα, 148.8 G, g) 2.0041; CF3OCH2CF2•, a (2Fα, 90.6 G; CF3•, a (3Fα, 142.4 G, a 13Cα, 271.6 G, g, 2.0031
    • 13Cα) = +271.6 G, g = 2.0031.
  • 12
    • 76049107057 scopus 로고    scopus 로고
    • The greater reactivity of bent σ-radicals relative to planar π-radials has been noted earlier in studies on aryl radicals, 13 and the influence of pyramidality on radical reactivities has been previously suggested in a study of α-hydroxyalkyl radicals.14
    • 14
  • 17
  • 18
    • 76049089664 scopus 로고    scopus 로고
    • 2•, a (2Fα) = 86.2 G, g = 2.0039.
    • 2•, a (2Fα) = 86.2 G, g = 2.0039.
  • 24
    • 76049083729 scopus 로고    scopus 로고
    • As would be expected for a reaction with a polar transition state the addition of perfluoroalkyl radicals to alkenes are faster in CH3CN than in Freon 113 with this solvent effect being greater for the more electron-rich alkenes. For example, the rate acceleration in CH3CN relative to the Freon solvent for addition to styrene by CF3• and CF3CF2CF2• is about a factor of 3, but for the addition of these two radicals to pentafluorostyrene the rate acceleration is only ca. 50, For comparison, Salikhov and Fischer22 have found that the rate of addition of the nucleophilic tert-butyl radical to (electron-deficient) acrylonitrile (IP, 10.9 eV) is also somewhat accelerated in more polar solvents, e.g, kadd (CH3CN)/kadd (c-C6H12), 2.8. In connection with the foregoing, we note that solvent effects on the rates of radical additions to alkenes
    • 24
  • 26
    • 76049100168 scopus 로고    scopus 로고
    • Unpublished results from this laboratory.
    • Unpublished results from this laboratory.
  • 28
    • 0028339426 scopus 로고    scopus 로고
    • 2 and related groups) preferentially exhibit nucleophilic character, see: Buttle, L. A.; Motherwell, W. B. Tetrahedron Lett. 1994, 35, 3995-3998. For other studies on the intramolecular cyclization of α,α- difluoroalkenyl radicals, see: ref 5a.
    • 2 and related groups) preferentially exhibit nucleophilic character, see: Buttle, L. A.; Motherwell, W. B. Tetrahedron Lett. 1994, 35, 3995-3998. For other studies on the intramolecular cyclization of α,α- difluoroalkenyl radicals, see: ref 5a.
  • 29
    • 76049112959 scopus 로고    scopus 로고
    • 30 It is clear that one or two α-fluorine atoms do not make an alkyl radical more electrophilic than the corresponding nonfluorinated species and may even make them slightly more nucleophilic.
    • 30 It is clear that one or two α-fluorine atoms do not make an alkyl radical more electrophilic than the corresponding nonfluorinated species and may even make them slightly more nucleophilic.
  • 31
    • 76049128599 scopus 로고    scopus 로고
    • NIST Standard Reference Database 25. NIST Structures and Properties Database and Estimation Program 1991; U. S. Department of Commerce: Gaithersburg, MD.
    • NIST Standard Reference Database 25. NIST Structures and Properties Database and Estimation Program 1991; U. S. Department of Commerce: Gaithersburg, MD.
  • 32
    • 76049124915 scopus 로고    scopus 로고
    • Buckley, T.; Johnson, R., III; Huie, R.; Zhang, A.; Kuo, S.; Klemm, B. (NIST) Unpublished results.
    • Buckley, T.; Johnson, R., III; Huie, R.; Zhang, A.; Kuo, S.; Klemm, B. (NIST) Unpublished results.
  • 34
    • 76049090856 scopus 로고    scopus 로고
    • 3 = 3.0 (see March, J. Advanced Organic Chemistry, 3rd ed., Wiley: New York, 1985; p 14).
    • 3 = 3.0 (see March, J. Advanced Organic Chemistry, 3rd ed., Wiley: New York, 1985; p 14).
  • 35
    • 76049123391 scopus 로고    scopus 로고
    • 3 is slightly more electron-withdrawing than F.
    • 3 is slightly more electron-withdrawing than F.
  • 36
    • 0028059645 scopus 로고    scopus 로고
    • Polar effects have also been demonstrated to be important in H-atom abstractions by perfluoroalkyl radicals, see: Dolbier, W. R, Jr, Rong, X. X. Tetrahedron Lett. 1994, 35, 6225-6228
    • Polar effects have also been demonstrated to be important in H-atom abstractions by perfluoroalkyl radicals, see: Dolbier, W. R., Jr.; Rong, X. X. Tetrahedron Lett. 1994, 35, 6225-6228.


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