Computational prediction of temperature dependence of 13C NMR lineshapes of planar molecules in structure I clathrate hydrates
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- Mohammadi-Manesh, H., Alavi, S., Woo, T.K. et al. J IRAN CHEM SOC (2013) 10: 659. doi:10.1007/s13738-012-0198-9
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We use the molecular dynamics-based method to predict the solid-state 13C NMR lineshape of a planar molecule in a nonspherical cage. Unlike linear molecules, three components of the chemical shielding tensor of a planar molecule are different which gives rise to a different lineshape and temperature dependence in the 13C NMR spectrum. We study the planar ethylene molecule in the oblate large cages of the structure I (sI) clathrate hydrate and extract the lineshapes from the angular distribution and dynamics at four temperatures (70, 150, 200, and 250 K) in the stability range of the hydrate. At low temperature, the C2H4 molecules have limited range of motion in the cages, but as the temperature is raised, they first gain greater rotational freedom about the molecular C=C axis, and then in other directions. These data allow for the calculation of the 13C NMR lineshapes of the C2H4 guests at each temperature.