Nuclear Magnetic Resonance Study of Ethylene Adsorbed on a Zeolite. Chemical-Shift Measurements

Publisher Website
Google Scholar
Abstract
The measurement is reported of the relative NMR chemical shifts of ethylene adsorbed on a zeolite in which the usual sodium cation has been exchanged with lithium, potassium, silver, cadmium, or barium ions. When measured relative to the proton signal from gas‐phase ethylene, the proton shifts in the adsorbed phase are to high field. The sample bulk susceptibility correction cannot explain the magnitude nor direction of the shift, nor can an analysis based on a simple consideration of the electric field of the cation. A linear correlation is observed between these high‐field shifts and certain frequency shifts in the infrared spectra of the adsorbed molecule. A discussion of this correlation is based on an analogy with the mechanism of the temperature‐dependent chemical shifts observed in gases. The hypothesis is offered that these chemical shifts result from deformations in the electronic and geometric structure of the adsorbed ethylene. A brief discussion of the low‐temperature wide‐line NMR spectra and the linewidth dependence on the spectrometer operating frequency is included.