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Steric effects in 31 P NMR spectra: ‘Gamma’ shielding in aliphatic phosphorus compounds
Author(s) -
Quin Louis D.,
Breen Joseph J.
Publication year - 1973
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/mrc.1270050106
Subject(s) - steric effects , electromagnetic shielding , chemical shift , chemistry , substituent , phosphorus , branching (polymer chemistry) , shielding effect , spectral line , carbon fibers , carbon chain , carbon 13 nmr , nmr spectra database , computational chemistry , organic chemistry , materials science , physics , layer (electronics) , astronomy , composite number , composite material
An examination of published 31 P NMR spectral data for aliphatic phosphorus compounds has revealed that chain lengthening and branching effects on the chemical shift can be interpreted in terms similar to those used for 13 C and 15 N shifts. For six families of phosphorus compounds, a β‐carbon substituent was shown to deshield phosphorus, while a γ‐carbon caused shielding. The effects are additive, and good agreement was obtained between 31 P shifts calculated with the appropriate constants and the experimental values. Shielding by γ‐carbon is indicative of the operation of a steric influence on 31 P chemical shifts, not heretofore articulated. The γ‐effect is also useful in explaining the unusually large shielding found in six‐membered cyclic phosphines.