Molecular motions in 2-iodo-2-methylpropane, (CH3)3CI. Proton nuclear magnetic resonance measurements at variable temperatures
- 1 January 1988
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics
- Vol. 84 (7) , 885-892
- https://doi.org/10.1039/f29888400885
Abstract
Polymorphism of (CH3)3CI has been confirmed by differential thermal analysis. There are two solid phases; one is a plastic-crystalline phase, phase I (235.7–240.4 K) and the other is a brittle crystal phase, phase II (below 235.7 K). Molecular motion in each phase has been studied by 1H n.m.r. relaxation times (T1, T2 and T1ρ). In phase II, the uniaxial molecular reorientation (C′ 3 reorientation) is faster than the methyl reorientation (C3 reorientation). The activation parameters of these motions are found to be Ea= 23.2 ± 0.4 kJ mol–1 and τ0=(2.9 ± 0.7)× 10–15 s for the C′ 3 reorientation, and Ea= 31.4+3.7 –2.1 kJ mol–1 and τ0=(1.1+2.4 –1.0)× 10–15 s for the C3 reorientation, respectively. In the plastic (phase I) overall molecular reorientation and molecular self-diffusion are believed to be responsible for T1 and T1ρ, and their activation parameters are found to be Ea= 7.9 ± 0.9 kJ mol–1 for the formation motion and Ea= 35.3+1.8 –1.4 kJ mol–1 and τ0=(2.1+2.3 –1.3)× 10–14 s for the latter motion, respectively. An activation energy of 11.4 ± 0.3 kJ mol–1 is found for the molecular motion in the liquid phase.Keywords
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