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Conformational free energy difference (–ΔG° value) of the methyl group in methylcyclohexane: an accurate determination by the direct, low-temperature nuclear magnetic resonance method
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1976
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Methyl GroupAccurate Determination–δG° ValueNatural SciencesSpectroscopyMagnetic ResonanceMinor ConformationMethyl AxialSpectra-structure CorrelationOrganic ChemistryConformational StudyMajor ConformationChemistryNuclear Magnetic Resonance SpectroscopyMedicineBiophysics
The low-temperature pulse Fourier transform 13C n.m.r. spectrum of methylcyclohexane, enriched with 13C in the methyl substituent, shows that the ratio of major conformation (methyl equatorial) to minor conformation (methyl axial) is 164 : 1 (0·6% methyl axial), corresponding to a conformational free energy difference at 172 K of 1·74 ± 0·06 kcal mol–1(7·30 ± 0·25 kJ mol–1).