Density-dependent magnetic shielding in gas phase 13C N.M.R.

Abstract

Density-dependent ¹³C nuclear magnetic shielding has been found for each of the pure gases CH₄, C₂H₆, C₂H₄, CO and CO₂, and for several binary mixtures of gases. For methane gas the density dependence is greater at higher temperatures in contrast to expectation and the observed temperature dependence of the shielding at zero density is attributable to nuclear motion. ¹³C magnetic shielding is considerably higher in the gas phase than in the liquid phase and the difference varies for chemically non-equivalent ¹³C nuclei by amounts which are well above the level of experimental error.