3lP-lH COUPLING CONSTANTS IN ETHYL ESTERS OF PHOSPHORUS ACIDS
4043
Three- and Four-Bond 31P-1H Coupling Constants and Geminal Proton Nonequivalence in Ethyl Esters of Phosphorus Acids by M. P. Williamson and C. E. Griffin Department of Chemistry, University of Pittsburgh, and Mellon Institute, Carnegie-Mellon University, Pittsburgh, Pennsylvania 16218 (Received April 10, 1968)
The POCHzCHsportions of the proton magnetic resonance spectra of 13 ethyl esters of tetracoordinate and four ethyl esters of trivalent phosphorus have been analyzed for the following parameters: V P H = 7.2012.55 He, ' J p H = 0.28-1.24 Hz, and *JHH = 7.02-7.13 Hz. The spectra of 13 of the esters were analyzed as A & X cases, but methylene proton nonequivalence was observed in three tetracoordinate esters and one trivalent ester. It was necessary to calculate the latter spectra as the sum of two A N N subspectra corresponding to the spin states CY and @ of the phosphorus. The compounds possessing nonequivalent methylene protons have no formal center of asymmetry at either carbon or phosphorus; the methylene protons possess different chemical shifts by virtue of internal asymmetry; Le., the ethoxyl groups are attached to phosphorus atoms bearing three different substituents. A number of studies of the pmr spectra of ethyl esters of phosphorus acids have appeared recently.'-' Particular interest has been shown in the magnitudes and relative signs of the four-bond (POCH2CH3) and three-bond (POCHzCH3) 31P-1H coupling constants in these systems; all the published data for these compounds are the result of first-order treatments. I n ~ ~ view of the small magnitudes (
