. Can. J. Chem. 55, 604 (1977). I3C chemical shifts and 13C-31P couplings are reported for 15 dialkylphosphonocyclohexanes. Data are compared to those for three related hydroxyphosphonates. Both direct and vicinal I3C"lP couplings are useful stereochemical probes. Materials with equatorial phosphorus exhibit one bond couplings larger by ca. 5 Hz than their axial counterparts. Vicinal couplings follow an approximate dihedral angle dependence but are attenuated by O H substitution. In addition to the expected gauche-y shielding effects, pentavalent phosphorus substituents induce minor (ca. 1 ppm) upfield shifts at carbons to which they bear an anti-periplanar relation. Chem. 55, 604 (1977). On rapporte les dtplacements chimiques du I3C et les constantes de couplage 13C-31P de 15 dialkylphosphonocyclohexanes. On compare ces donnees avec celles de trois hydroxyphosphonates voisins. Les couplages directs et vicinaux '3C-3'P sont tous les deux des sondes stereochimiques utiles. Les composts avec un phosphore en position Cquatoriale prksentent des couplages a travers une liaison qui sont plus grands par environ 5 Hz que leurs contreparties axiales. I1 existe une dependance approximative entre les couplages vicinaux et I'angle diedre; ces couplages sont toutefois attenues par I'introduction d'un OH. En plus des effets de blindage y gauche attendus, les phosphores pentavalents induisent au niveau des carbones par rapport auxquels ils ont une relation anti-periplanaire, des deplacements chimiques mineurs (environ 1 ppm) vers les hauts champs.[Traduit par le journal] Introduction It has been a decade since the first report (1) of the utility of 13C nmr as a technique for the stereochemical analysis of cyclohexyl compounds and the method is now well established (2, 3). An area of recent interest has been in the application of I3C nmr to conformational effects among cyclohexyl phosphorus compounds containing tri-and tetravalent phosphorus atoms (4). Herein we report our findings for a series of substituted dimethyl-, diethyl-, and diisopropylphosphonocyclohexanes in which the influence of axial and equatorial pentavalent phosphorus atoms on the carbon shifts and 13C-31P couplings has been examined.Results are compared with earlier data for cis-and trans-4-tert-butyl-1-hydroxy-1-dimethylphosphonocyclohexanes (5) to clarify the effects of OH substitution on the nmr parameters. Employing the isomeric 4-tert-butyl cyclohexyl compounds as models as well as the known influence of methyl stereochemistry on carbon shifts (6), the preferred geometries of some pre-
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