wizyta

od 2020-09-20

Title: Molecular motions and polymorphic properties of solid 2-methyl-2-propaneselenol as studied by NMR

Source: Molecular Physics

Year : 1988

Abstract:

The spin-lattice relaxation times (T1, T1ρ and T1D) as well as the second moment of the proton spectrum for (CH3)3CSeH have been studied between 77 K and room temperature. The data reveal four transition temperatures 95, 117, 144 and 168 K, the last one the melting point, and provide some basic information on the motional properties of the respective four solid state phases. In the lowest temperature phase IV there is uniaxial C′3 motion and methyl groups C3 rotation. The activation energy for the C′ 3 motion dominating T 1 relaxation is found to be 5·5 kJ mol-1. The spin-lattice relaxation in phase III reflects a complex motional behaviour of the methyl groups, consistent with a distribution of correlation times. The transition to phase II involves a new motion, possibly restricted molecular reorientation, of frequency 7-28 MHz. There is considerably molecular freedom in the highest temperature phase I, enabling molecular tumbling as well as self-diffusion of molecules to occur, a common feature for plastic crystals.

DOI: 10.1080/00268978800101891   (Pobrane:  aktualizowanie)