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13 C and 31 P NMR studies of configurational and conformational effects in 1‐Phenyl‐4‐phosphorinanones and their 1‐selenides
Author(s) -
Pietrusiewicz K. Michał
Publication year - 1983
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/omr.1270210602
Subject(s) - chemistry , dihedral angle , substituent , crystallography , selenide , lone pair , carbon 13 nmr , nmr spectra database , nuclear magnetic resonance spectroscopy , chemical shift , stereochemistry , selenium , spectral line , hydrogen bond , molecule , organic chemistry , physics , astronomy
Carbon‐13 and 31 P NMR data are reported for 1‐phenyl‐4‐phosphorinanone and its 1‐selenide, as well as for two anancomeric 1‐phenyl‐3,5‐dimethyl‐4‐phosphorinanones and their 1‐selenides. The conformational free energy of the P ‐phenyl substituent in 1‐phenyl‐4‐phosphorinanone is estimated to be Δ G ° = 0.81 kcal mol −1 ( ca 80% axial) in chloroform, and this result is consistent with both 13 C NMR shielding and coupling data. The γ effects of a single atom substituent on phosphorus are found to be small in the case of selenium; information in the literature indicates significant downfield‐shifting γ e effects due to equatorial oxygen and sulphur substituents in phosphorinanes. In selenides, the shift for the aromatic C‐ ipso carbon in the axial isomer is further downfield than in the equatorial isomer, an observation not precedented in the literature. In the discussion of P‐C coupling data a ‘second order’ Karplus‐like relationship is invoked for 3 J (PC), which is dependent both on the dihedral angle and on the orientation of the phosphorus lone pair in phosphines. The one‐bond P‐C‐ ipso coupling in selenides is identical for all three selenides studied, regardless of the stereochemistry at phosphorus. Similar lack of substantial differentiation is noted for one‐bond P‐Se coupling. A possible origin of this phenomenon is discussed in terms of diminution of the phosphorus charge contribution to the Fermi contact term. From 31 P NMR data a high stereodependence of selenylation shifts is apparent, and greater shifts (by ca 20 ppm) are observed when selenium is bound to phosphorus in the more crowded (axial) position. In anancomeric (conformationally biased) phosphines, the isomer with the axial phenyl group has the 31 P signal at lower field. This is consistent with observations made previously for rigid 1‐phenylphosphorinanes.