Rotator phase

On heating lower n-paraffins the so-called rotator phases occur a few degrees below the melting point they are either hexagonal or nearly so [78-82]. This is the earliest recognized example of a hexagonal phase and thus the best known. 

Regarding Case 1, it is known that the rotator phases of -paraffins are three dimensionally ordered solids with molecules in aW-trans conformation, their specific volumes, Vh, and specific entropies, Sh, are closer to corresponding values and for the orthorhombic phases than they are to those for the melt and Sm In contrast,... 

Figure 8 P-T phase diagrams of -paraffins and PE. shaded areas indicate the regions of the stable hexagonal (or rotator) phase. (From Ref. 86.)...

Conversely, the high-pressure hexagonal phase is one of high entropy for which the reverse inequality is true. In lower -paraffins, the occurrence of the rotator phase at atmospheric pressure is due to the fact that the orthorhombic-hexagonal (or rotator) transition temperature, is lower than the temperature of fusion of... 

The heat of fusion of the rotator phase in n-paraffms is 38-40 cal/g, while AHo- m for PE irradiated with 1000 Mrad is about 29 cal/g. The corresponding value of AHo->m for hexagonal PE at high pressure (500 MPa) is only around 15 cal/g. Thermograms of constrained PE fibers showed similarly low heats of fusion of the hexagonal phase. 

The cross-sectional area per chain in the hexagonal lattice of irradiated PE varies between 20.6 and 22.0 A. It is, thus, always greater than the cross-sectional area in the rotator phase in paraffins (19.5-20.0 A ), but on average somewhat smaller than that in constrained PE fibers above 7, /, (21.4-22.7 A ). An ethylene-propylene diene copolymer with approximately 64%, 32%, and 4% by weight of each component, respectively, was found to contain hexagonal crystals with a cross-sectional area per chain of 20.3 A". 

With concern to the high internal mobility of the molecules in the high temperature solid state phase, some parallelism to n-alkanes can be stated. In the pseudohexagonal (rotator) phase the latter are also characterized by fast molecular motions. For discrimination and according to Pfitzer 14) and Dale 13) in the following the term pseudorotator phase is used for the mobil crystalline state of cyclic molecules. 

Pseudo-affine deformation scheme 96, 97 Pseudohexagonal (rotator) phase 67 Pseudorotator phase 67 Pulsed NMR techniques 30... 

In this manner the necessary condition (4.16) of the line narrowing effect is satisfied only for the doublet that belongs to the Q-branch. This result reflects the fact that a rotational phase shift does not affect Q-branch... 

The rotational phase shift 5, which cannot exceed a mean angle of a molecular rotation during collisional time (anc), is certainly small in the case of non-adiabatic collisions. This condition is exactly that needed for anisotropic scattering (or IR absorption) spectrum narrowing, just as vibrational dephasing must be weak for an isotropic spectrum to narrow. 

Bachman, R.E., Fioritto, M.S., Fetics, S.K and Cocker, T.M. (2001) The Structural and Functional Equivalence of Aurophilic and Hydrogen Bonding Evidence for the First Examples of Rotator Phases Induced by Aurophilic Bonding. Journal of the American Chemical Society, 123, 5376-5377. 

The reactant molecule BC is specified to be in an initial vibrational v and rotational state 7, which determines p and allows R to be set to the maximum bond extension compatible with total vibrational energy. The initial relative velocity uR may be varied systematically or it may be chosen at random from Boltzmann distribution function. The orientation angle, which specify rotational phase and impact parameter b are selected at random. 

Figure 4.31 Snapshot picture of molecular dynamics of CjsH g, tricosane, viewed along the a axis. A bilayer is shown for (a) the crystalline phase at 31 IK and (b) the rotator phase at 315K. For clarity no H atoms, only the central C atoms along with a few terminal C atoms are shown. Note the disorder in the central C atoms in the rotator phase which is predominantly along the longitudinal axis (after Ryckaert et al, 1989).

In addition to the synthetic advances, the study of the optical properties of these species is a growing field. Many complexes which exhibit these interactions are luminescent. Other interesting points are the induction of rotator phases or the modulation of magnetic properties by designing the appropriate heterometallic complexes. Gold-gold interactions are still a hot topic in gold chemistry. This is evidenced in the observation that some complexes which exhibit these interactions, characterized some years ago, are revisited and modified in order to study their properties. 

Fig. 3 Approximate pressure-temperature rotational phase diagram of molecular C70. See text for details...

Cantor, R.S. Dill, K.A. Statistical thermodynamic theory for the melting of n-alkanes from their rotator phases. Macromolecules 1985, 18, 1875. 

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