Proton Magnetic Resonance Spectra of Compounds of the Type X(C2H5)n. Relative Signs of the X-H Spin Coupling Constants

Abstract

The high-resolution proton magnetic resonance spectra of phosphorus triethyl, tin tetraethyl, and lead tetraethyl have been studied at both 40 Mc and 60 Mc. The various spin-spin coupling constants (J) and the proton internal chemical shift (δ) values for these molecules have been obtained by an analysis of the spectra as A3B2 and A3B2X systems. (A denotes CH3 group protons, B the CH2 group protons, and X is a nucleus other than the proton with spin ½ such as P31, Sn117, Sn119, or Pb207.) In phosphorus triethyl it is found that JAX and JBX have opposite signs. The proton magnetic resonance spectrum of tin tetraethyl is a complex A3B2 type spectrum even at 60 Mc with ``satellite'' lines from naturally present Sn117 (C2H5)4 (7.67%) and Sn119 (C2H5)4 (8.68%) in the sample. Analysis of the satellite spectrum as an A3B2 type shows that JAX and JBX have opposite signs (here X=Sn117 or Sn119). The proton resonance spectrum of lead tetraethyl has been reinvestigated and it is found that the satellite lines due to Pb207 (C2H5)4 do not show any asymmetry, in contrast with earlier observations of Baker. Probable causes for Baker's results are given and it is shown theoretically and experimentally that such an asymmetry does not truly exist. The coupling constants JAX and JBX are found to have opposite signs in lead tetraethyl also.