X-ray diffraction study of some liquid alkanes
- Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (USA)
The structure of the liquids {ital n}-heptane, {ital n}-decane, {ital n}-pentadecane, and {ital n}-eicosane was investigated using x-ray diffraction. The data are analyzed using group scattering factors for -CH{sub 2} and -CH{sub 3} sites which permits extraction of the carbon--carbon structure and distribution functions. Analysis has yielded the short-range intramolecular distances and bond angles, the average torsional angles for the {ital gauche} and {ital trans} rotational isomer segments, and the {ital gauche}/{ital trans} populations. Intramolecular carbon--carbon distances at 3.11{plus minus}0.03 A and 3.94 {plus minus}0.01 A are assigned to {ital gauche} and {ital trans} molecular segments, respectively. The average torsion angle of the gauche segments is near 64{plus minus}2{degree}, and the {ital trans} segments appear to be twisted from a planar conformation by 10{plus minus}2{degree}. The average fraction of {ital gauche} segments in the liquid phase of these alkanes is approximately 45{plus minus}8%, slightly higher than in the gas phase. The conformational equilibrium of the {ital n}-alkanes is only minimally perturbed by the intermolecular interactions in the liquid phase, and the results are inconsistent with the possibility of a large fraction of extended chains (or chain segments) in the liquid.
- DOE Contract Number:
- AC05-84OR21400; AC05-76OR00033
- OSTI ID:
- 7122205
- Journal Information:
- Journal of Chemical Physics; (USA), Journal Name: Journal of Chemical Physics; (USA) Vol. 92:9; ISSN JCPSA; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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