o-Terphenyl: flips of the end rings in the crystal phase

Abstract

We demonstrate by selective saturation deuteron NMR experiments on a crystal of selectively deuterated o-terphenyl (OTP) that both end rings I and II attached to the central ring undergo thermally activated flip motions. In crystals of OTP, the end rings I and II are not symmetry related, their dynamics can be different and, in fact, is different, although mutual steric hindrance of the rings suggests a strong correlation. We measured the rates k I and k II of the flips of both end rings I and II as a function of temperature. We find that, independent of the temperature, k I exceeds k II by roughly a factor of 100. This result excludes correlated flips of rings I and II in the sense that a flip of one ring necessarily entails a flip of the other. The activation energies EaI and EaII of the two flip processes turn out to be equal (80.5 kJ mol−1) within experimental errors. This is taken as a hint that the flips are, after all, related to each other. A mechanism is proposed of how this is possible under the constraint k I » k II

Structure and Dynamic Properties of Solid l-Tyrosine-Ethylester as Seen by 13C MAS NMR

“…51 kJ mol -1 in a penicillin salt to ca. 111 kJ mol -1 in another pencillin derivative 20 and many other examples such as para-iodo-benzene, biphenyl, or other compounds [18][19][20][21][22][23][24][25][26] displaying activation energies between these two extremes. The activation energy of the π flips of the phenyl ring in solid TEE is thus one of the lowest activation barriers for this kind of dynamic disorder in organic solids observed so far.…”

A volumetric and dielectric study of m-fluoroaniline under pressure

“…On the other hand, also small organic molecules are not as rigid as commonly believed. This has been demonstrated not only for the rotation of the methyl group in toluene [12], but also for the phenyl rings in O-terphenyl [13,14]. From the comparison of different chlorotoluene supercooled liquids it has been concluded that the origin of the secondary relaxation of that glass is mainly due to the rotation of the CH 2 Cl subgroup [15].…”

Three-Dimensional Nano-objects Evolving from a Two-Dimensional Layer Technology

“…An extensive theoretical introduction to CODEX can be found in the literature [15]. Note Added in Proof: After completion of this work we learnt about a recent study by Haeberlen et al, [16] who detected phenyl flips even in the crystal phase of o-terphenyl.…”