Experimental determination of the conformational free energies (A values) of fluorinated substituents in cyclohexane by dynamic F-19 NMR spectroscopy. Part 2. Extension to fluoromethyl, difluoromethyl, pentafluoroethyl, trifluoromethylthio and trifluoromethoxy groups

The synthesis of monosubstituted and 1,4-substituted cyclohexanes bearing one of the title groups is described. The conformational analysis of these compounds was studied by F-19 NMR spectroscopy at various temperatures. Chemical shifts for each conformer above the coalescence temperature were obtai...

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Bibliographic Details
Published inNew journal of chemistry Vol. 30; no. 3; pp. 447 - 457
Main Authors Carcenac, Y, Tordeux, M, Wakselman, C, Diter, P
Format Journal Article
LanguageEnglish
Published CAMBRIDGE Royal Soc Chemistry 01.01.2006
Subjects
Chemistry
Chemistry, Multidisciplinary
Physical Sciences
Science & Technology
CONVENIENT SYNTHESIS
ALCOHOLS
C-13
HYDROGENATION
TEMPERATURE
ESTERS
EQUILIBRIUM
HYPERCONJUGATIVE INTERACTIONS
NUCLEAR MAGNETIC-RESONANCE
OXIDATIVE DESULFURIZATION-FLUORINATION
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Summary:The synthesis of monosubstituted and 1,4-substituted cyclohexanes bearing one of the title groups is described. The conformational analysis of these compounds was studied by F-19 NMR spectroscopy at various temperatures. Chemical shifts for each conformer above the coalescence temperature were obtained by binomial regression from low temperature values, allowing the high precision determination of the equilibrium constants, and the corresponding thermodynamic parameters (Delta G degrees, Delta H degrees, Delta S degrees) of the fluorinated substituents. For A values (-Delta G degrees(298K)), the following averaged data were obtained: 1.59 (CFH2), 1.85 (CF2H), 2.67 (C2F5), 0.79 (OCF3) and 1.18 (SCF3) [ in kcal mol(-1)].
ISSN:1144-0546
1369-9261
DOI:10.1039/b516641a