Experimental and computational 13C NMR studies of guest molecule conformations in large cages of structure H clathrate hydrates

Binary structure H clathrate hydrates of large alkane molecules with methane help gas have been synthesized and their lattice structure verified by powder X-ray diffraction measurements. The chemical shifts of the carbon atoms of the guest molecules in the solid-state 13C NMR spectra in the hydrate phase show significant up-field shifts compared to the pure liquid guest species. Quantum chemistry chemical shift calculations of different conformers of the guest molecules have been performed and compared with the experimental pure guest and guest in hydrate 13C NMR spectra. These comparisons allow us to determine the relative contributions of conformation changes of the guests in the cages and the guest-host dipolar coupling to the changes in 13C NMR chemical shift upon enclathration. The guests studied in this work include 2-methylbutane, 2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylpentane, 3-methylpentane, n-pentane, n-hexane, methylcyclopentane and methylcyclohexane.Peer reviewed: YesNRC publication: Ye