{sup 1}H and {sup 19}F spin-lattice relaxation and CH{sub 3} or CF{sub 3} reorientation in molecular solids containing both H and F atoms
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr., La Jolla, California 92093-0358 (United States)
The dynamics of methyl (CH{sub 3}) and fluoromethyl (CF{sub 3}) groups in organic molecular (van der Waals) solids can be exploited to survey their local environments. We report solid state {sup 1}H and {sup 19}F spin-lattice relaxation experiments in polycrystalline 3-trifluoromethoxycinnamic acid, along with an X-ray diffraction determination of the molecular and crystal structure, to investigate the intramolecular and intermolecular interactions that determine the properties that characterize the CF{sub 3} reorientation. The molecule is of no particular interest; it simply provides a motionless backbone (on the nuclear magnetic resonance (NMR) time scale) to investigate CF{sub 3} reorientation occurring on the NMR time scale. The effects of {sup 19}F–{sup 19}F and {sup 19}F–{sup 1}H spin-spin dipolar interactions on the complicated nonexponential NMR relaxation provide independent inputs into determining a model for CF{sub 3} reorientation. As such, these experiments provide much more information than when only one spin species (usually {sup 1}H) is present. In Sec. IV, which can be read immediately after the Introduction without reading the rest of the paper, we compare the barrier to CH{sub 3} and CF{sub 3} reorientation in seven organic solids and separate this barrier into intramolecular and intermolecular components.
- OSTI ID:
- 22660847
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 15 Vol. 144; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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