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od 2020-09-20

Title: Composite motion of molecular groups in solid triethylphosphine oxide as studied by NMR

Source: Journal of Magnetic Resonance (1969)

Year : 1982

Abstract:

Second moments and spin-lattice relaxation times in the laboratory and rotating frames were determined for solid triethylphosphine oxide (C2H5)3PO over the temperature range 77 to 320 K. Theoretical expressions were derived for the T1 and T1π relaxation behavior of the ethyl group in (C2H5)3PO undergoing the composite motion of reorientation about C-P axis, P-O axis, and isotropic tumbling of the (C2H5)3PO molecule, under the assumption of rapid spin exchange between the CH2 and CH3 groups and internal motion of the CH3 group about its threefold axis within the ethyl group. These expressions were applied to analyze the experimental T1 and T1π data, and the results obtained along with the second moment measurement allowed us to assess the following motions: (i) methyl group reorientation about its C3 axis, (ii) ethyl group reorientation about the C-P axis, and (iii) molecular reorientation about the P-O axis, with activation energies of about 8.3, about 22.9, and 40.1 kJ/mol, respectively.

DOI: 10.1016/0022-2364(82)90047-6   (Pobrane:  aktualizowanie)