Interactions intramoléculaires: XXIII—Constantes de couplage et interactions gauches avec un groupement t-butyle (cyclohexanones disubstituées 3, 4) |
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Authors: | Ronald Lafrance Jean-Pierre Aycard Jeanne Berger Hubert Bodot |
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Abstract: | The 1H NMR spectra of a series of cis and trans-3R,4 X-cyclohexanones (-2,2,6,6-d4) are analysed. By comparison of their 3J coupling constants with those of cyclohexane homologues we obtain information about the chair–chair equilibrium constants for R = CH3, X = CN, the chair structure of cis isomers with an equatorial t-butyl group, and a conformational heterogeneity with trans (CH3)3C and CN groups. This latter situation is analysed by means of a simplified but controlled Karplus relationship, on the basis of a mixture of two conformers; this involves a diequatorial chair and a boat form with a dihedral angle Φ34 of about ?6°. |
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