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13 Fluorination of aliphatic substrates

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Organic and Inorganic Fluorine Chemistry
This chapter is in the book Organic and Inorganic Fluorine Chemistry
13 Fluorinationofaliphaticsubstrates13.1 Generaltrendsinthesynthesisofaliphaticorganofluorinecompounds13.1.1 ThegeneralfluorineeffectPrior to discussing detailed synthetic approaches toward aliphatic organofluorinecompounds, two general trends need to be pointed out. Many of the fluorinationmethods in the following subchapters include side-reactions, especially migrationsand rearrangements, as for example, inter- and intramolecular halogen transfer. Ingeneral, halogen migration is preferentially observed under drastic reaction condi-tions and in presence of strong Lewis acids like SbCl5, AlCl3or AlBr3(Scheme 13.1)[2828]. If possible, fluorine substituents clearly tend to accumulate at one carbonatom,renderingtrifluoromethyl-andgeminaldifluoromethyl-derivativesthethermo-dynamicallyfavoredproducts.Scheme13.1:Inter-andintramolecularhalogenmigrationcatalyzedbyLewisacids.The occurrence of this behavior, often referred to as “general fluorine effect,” canbe rationalized by energetic stabilization due to resonance structures (Figure 13.1).At electron-poor sp3-carbon centers, the lone-pairs of the fluorine substituents canshift some electron-density toward the positively polarized carbon atom byπ-back-donation.Thisresultsinnegativehyperconjugationandtheformationofionicreso-nancestructures.https://doi.org/10.1515/9783110659337-016
© 2021 Walter de Gruyter GmbH, Berlin/Munich/Boston

13 Fluorinationofaliphaticsubstrates13.1 Generaltrendsinthesynthesisofaliphaticorganofluorinecompounds13.1.1 ThegeneralfluorineeffectPrior to discussing detailed synthetic approaches toward aliphatic organofluorinecompounds, two general trends need to be pointed out. Many of the fluorinationmethods in the following subchapters include side-reactions, especially migrationsand rearrangements, as for example, inter- and intramolecular halogen transfer. Ingeneral, halogen migration is preferentially observed under drastic reaction condi-tions and in presence of strong Lewis acids like SbCl5, AlCl3or AlBr3(Scheme 13.1)[2828]. If possible, fluorine substituents clearly tend to accumulate at one carbonatom,renderingtrifluoromethyl-andgeminaldifluoromethyl-derivativesthethermo-dynamicallyfavoredproducts.Scheme13.1:Inter-andintramolecularhalogenmigrationcatalyzedbyLewisacids.The occurrence of this behavior, often referred to as “general fluorine effect,” canbe rationalized by energetic stabilization due to resonance structures (Figure 13.1).At electron-poor sp3-carbon centers, the lone-pairs of the fluorine substituents canshift some electron-density toward the positively polarized carbon atom byπ-back-donation.Thisresultsinnegativehyperconjugationandtheformationofionicreso-nancestructures.https://doi.org/10.1515/9783110659337-016
© 2021 Walter de Gruyter GmbH, Berlin/Munich/Boston

Chapters in this book

  1. Frontmatter I
  2. Preface V
  3. Foreword VII
  4. Contents IX
  5. Part A: Introduction to fluorine chemistry
  6. Introduction to fluorine chemistry 1
  7. 1 Sources of fluorine in nature 5
  8. 2 Elemental fluorine 9
  9. 3 Hydrogen fluoride 15
  10. 4 Preparation of fluorinated compounds [35] 23
  11. 5 Common solid-state structures of inorganic fluorides [35] 31
  12. 6 Properties of fluorinated compounds 35
  13. 7 Health and environmental aspects of fluorinated compounds 37
  14. 8 19F-NMR – an important analytical tool for fluorine chemists [53, 54] 43
  15. Part B: Inorganic fluorine chemistry
  16. Inorganic fluorine chemistry 53
  17. 9 Main group element fluorides 55
  18. 10 Transition metal fluorides and rare earth metal fluorides 161
  19. Part C: Organic fluorine chemistry
  20. Organic fluorine chemistry 281
  21. 11 Fluoroorganic compounds – unusual properties and versatile applications 283
  22. 12 General reaction types and reagents for the introduction of fluorine 301
  23. 13 Fluorination of aliphatic substrates 319
  24. 14 Fluorination of (hetero-) aromatic compounds 415
  25. 15 Preparation of fluorinated olefins and acetylenes 453
  26. 16 Solutions to study questions 479
  27. Bibliography 537
  28. Index 617
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https://doi.org/10.1515/9783110659337-016

Chapters in this book

  1. Frontmatter I
  2. Preface V
  3. Foreword VII
  4. Contents IX
  5. Part A: Introduction to fluorine chemistry
  6. Introduction to fluorine chemistry 1
  7. 1 Sources of fluorine in nature 5
  8. 2 Elemental fluorine 9
  9. 3 Hydrogen fluoride 15
  10. 4 Preparation of fluorinated compounds [35] 23
  11. 5 Common solid-state structures of inorganic fluorides [35] 31
  12. 6 Properties of fluorinated compounds 35
  13. 7 Health and environmental aspects of fluorinated compounds 37
  14. 8 19F-NMR – an important analytical tool for fluorine chemists [53, 54] 43
  15. Part B: Inorganic fluorine chemistry
  16. Inorganic fluorine chemistry 53
  17. 9 Main group element fluorides 55
  18. 10 Transition metal fluorides and rare earth metal fluorides 161
  19. Part C: Organic fluorine chemistry
  20. Organic fluorine chemistry 281
  21. 11 Fluoroorganic compounds – unusual properties and versatile applications 283
  22. 12 General reaction types and reagents for the introduction of fluorine 301
  23. 13 Fluorination of aliphatic substrates 319
  24. 14 Fluorination of (hetero-) aromatic compounds 415
  25. 15 Preparation of fluorinated olefins and acetylenes 453
  26. 16 Solutions to study questions 479
  27. Bibliography 537
  28. Index 617
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