Dependence of the /sup 13/C and the /sup 1/H nuclear magnetic shielding on bond extension in methane

Journal Article · Thu Nov 15 04:00:00 EST 1984 · J. Chem. Phys.; (United States)

OSTI ID:6364131

Osten, H; Jameson, C J

The mean bond displacements <..delta..r> in the methane isotopic homologous series /sup 13//sup ///sup 12/CX/sub 4-n/Y/sub n/ (X, Y = H, D, T) at 300 K, and the temperature dependence of <..delta..r/sub CH/> in /sup 13/CH/sub 4/ from 250 to 350 K were calculated. With the assumption that the linear terms are sufficient to account for the isotope shifts, we determine from the /sup 2//sup ///sup 1/H-induced /sup 13/C isotope shift an empirical value of(partialsigma/sup C//partial..delta..r/sub CH/)/sub e/ = -35 +- 3 ppm/A. This predicts a temperature dependence in the /sup 13/C resonance in CH/sub 4/ gas in the zero-pressure limit of 2.7 x 10/sup -2/ ppm over 100 /sup 0/, which explains why it could not be observed. We observed the /sup 13//sup ///sup 12/C-induced /sup 1/H isotope shift in CH/sub 4/, -0.0024 ppm. With the same mean bond displacements, this isotope shift gives an estimate of (partialsigmai-italic /partial..delta..ri-italic )/sub e/ = -38 +- 3 ppm/A. From the reported /sup 2//sup ///sup 1/H-induced two-bond /sup 1/H isotope shift in CH/sub 4/, -0.016 ppm, using the mean bond displacements and the derivative obtained from the /sup 13//sup ///sup 12/C-induced one-bond isotope shift, we get an estimate of (partialsigmai-italic/ partial..delta..rj-italic) /sub e/ = -1.3 +- 0.2 ppm/A.

• Research Organization: Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60680
• OSTI ID: 6364131
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 81:10; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ALKANES
CARBON 13
CARBON ISOTOPES
EVEN-ODD NUCLEI
FLUIDS
GASES
HYDROCARBONS
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
LOW TEMPERATURE
MEDIUM TEMPERATURE
METHANE
NMR SPECTRA
NUCLEI
ORGANIC COMPOUNDS
SPECTRA
STABLE ISOTOPES
TEMPERATURE DEPENDENCE