Urea inclusion compounds dynamic properties

In this article, an overview of stmctural aspects of urea inclusion compounds is provided, and some of the interesting properties of these materials, such as the dynamic and conformational properties of the guest molecules, chemical reactions, and applied aspects, are elaborated upon. Also highlighted are the types of techniques used to investigate these properties. Several review articles have been published on urea inclusion compounds,and they contain comprehensive lists of references to the original literature in this field. The reader is encouraged to consult these review articles, and the original papers cited therein, in order to obtain more information. 

At sufficiently low temperatu es, most conventional urea inclusion compounds undergo phase transitions associated with changes in the symmetry of the host structure and changes in the dynamic properties of the guest molecules. For alkanelurea and oc.co-dibromoalkane/urea inclusion compounds, structural and dynamic " aspects of these phase transitions have been investigated extensively using a variety of techniques. Qualitatively, the alkane/ urea and a,co-dibromoalkane/urea inclusion compounds behave in a siinilar way with respect to these transitions. 

Several techniques have been used to investigate dynamic properties of urea inclusion compounds, including solid-state NMR, incoherent quasielastic neutron scattering ESR, molecular dynamics simulation, Raman, infrared, dielectric loss, and x-ray diffraction. In addition to investigations of the dynamics of the guest molecules, the dynamic properties of the urea molecules have also been studied. 

Although the alkanelurea and a,co-dibromoalkane/urea inclusion compounds exhibit similar dynamic behavior, the dynamic properties of other urea inclusion compounds can differ substantially. The dynamic properties of dioctanoyl peroxide guest molecules have been investi-gated by a combined approach employing IQNS and H-NMR. Both techniques indicate that the reorientation of the guest molecules about the tunnel axis can be described by a model of uniaxial rotational diffusion in a... 

Much early work relating to chemical reactions in urea inclusion compounds focused on studies,primarily using ESR spectroscopy, of radicals generated from the guest molecules by x-ray irradiation, and provided fundamental information about the spin density and its anisotropy in a variety of radical species. Subsequently, a number of other workers have used ESR spectroscopy to identify radicals formed by x-ray or y-ray irradiation and to study the dynamic, chemical, and electronic properties of these radicals.[ Details of these studies were reviewed elsewhere. 

El Baghdadi, A. Dufourc. E.J. Cuillaume. F. Chain end dynamical and conformational properties of n-nonadecane molecules in urea inclusion compounds A study by deuterium NMR spectroscopy. J. Phys. Chem. 1996. 100. 1746. 

Solid-state and C NMR spectroscopy has been used to study the structural properties of 1-bromodecane in urea. It was found that the end groups of the guest molecules are randomly arranged. The dynamic characteristics of 1-bromodecane in urea inclusion compounds were probed by variable-temperature solid-state H NMR speetroseopy (line shapes, spin-spin relaxation T2, spin-lattiee relaxation Tix and Tiq) between... 

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