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Intermolecular and intramolecular effects on the 1 H and 13 C shielding in some gaseous hydrocarbons at various temperatures—experimental results
Author(s) -
Bennett Brian,
Raynes William Thomas
Publication year - 1991
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260290915
Subject(s) - chemistry , electromagnetic shielding , intermolecular force , intramolecular force , proton , propane , analytical chemistry (journal) , atmospheric temperature range , thermodynamics , molecule , organic chemistry , nuclear physics , physics , quantum mechanics
The proton and 13 C shielding constants in CH 4 , C 2 H 6 , C 3 H 8 , and some other gaseous hydrocarbons have been studied as functions of density at temperatures in the range 180–370 K. The linear coefficients describing the density dependence of the shielding, after correcting for bulk susceptibility, increase substantially as the temperature is reduced, indicating stronger intermolecular interactions. (Some of the required magnetic susceptibilities were determined in this work by an NMR method). The 13 C measurements for CH 4 are close to those of an earlier study; the results for the other gases are new. The linear coefficient is substantially greater for the carbon shielding of the methyl group in propane than for the methylene group at any temperature, but there is virtually no distinction between the linear coefficients for the proton shielding in this gas. Values for do 0 /d T , the temperature dependence of the shielding extrapolated to zero density, are also presented for both proton and 13 C shielding in the hydrocarbons. They are positive and negative in different instances. It is shown from this and earlier gas‐phase studies that standard literature values of the methane 13 C shielding relative to the 13 shielding in the other hydrocarbons are in error.