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Studies of Layered Double Hydroxides (open access)

Studies of Layered Double Hydroxides

This work concerns some synthetic processes and basic properties of layered double hydroxides (LDHs). A series of LDHs, a family of newly developed materials found to have many potential uses in industry, were investigated in relating to the origin of life on early Earth. In this work, I successfully intercalated some inorganic as well as organic species. Ammonium, accompanied with ferrocyanide ion, can enter the layered space. It was found there were two kin go f intercalated ferrocyanide species: one is that exchanged with anions and became a part of layered double hydroxide, while the other is suggested to be related to ammonium ferrocyanide neutral species. Formaldehyde, ethanolamine and formate can also be involved into LDHs. To improve the crystallinity, homogeneous precipitation method, which used Urea and Hexamine, was employed. The results reveal the success in the case by Urea but not in that by Hexamine. Annealing could also be used for this purpose. However, it needs to be preocessed in its mother liquor; no improvement on the crystallinity if the material has been washed before annealing.
Date: August 1995
Creator: Zhao, Jingxian
System: The UNT Digital Library
Molecular Modeling Study of Oxidative Degradation of Polyperfluoroethers Catalyzed by Iron Fluoride Surfaces : An Extended Hückel Theory Approach (open access)

Molecular Modeling Study of Oxidative Degradation of Polyperfluoroethers Catalyzed by Iron Fluoride Surfaces : An Extended Hückel Theory Approach

Extended Hückel methods are known to be a useful tool in understanding surface phenomena. Important quantities about atoms and chemical bonds can be obtained from this computationally simple method, although caution must be exercised in interpreting the results. Application of Extended Hückel calculations to large metal clusters reveals the role of d orbitals in solids. Basic ideas of constructing model compounds have been developed. Several model systems for surface chemisorption processes are constructed in order to understand the surface catalyzed oxidative degradation of polyperfluoroethers. The activation of oxygen molecules can be explained. The Lewis acid character of the iron fluoride surface can be predicted. Based on these results, mechanisms of the degradation processes are discussed.
Date: May 1995
Creator: Wang, Yanbin
System: The UNT Digital Library
Investigation of Copper Out-Plating Mechanism on Silicon Wafer Surface (open access)

Investigation of Copper Out-Plating Mechanism on Silicon Wafer Surface

As the miniaturization keeps decreasing in semiconductor device fabrication, metal contamination on silicon surfaces becomes critical. An investigation of the fundamental mechanism of metal contamination process on silicon surface is therefore important. Kinetics and thermodynamics of the copper out-plating process on silicon surfaces in diluted HF solutions are both evaluated by several analytical methods.
Date: August 1995
Creator: Chien, Hsu-Yueh
System: The UNT Digital Library
I. On the Mechanism of Acid Promoted Rearrangement of PCU-Derived Pinacols II. Synthesis of a Trimethyltrishomocubyl Helical Tubuland Diol (open access)

I. On the Mechanism of Acid Promoted Rearrangement of PCU-Derived Pinacols II. Synthesis of a Trimethyltrishomocubyl Helical Tubuland Diol

I. Reductive dimerization of pentacyclo[5.4.0.0.^2,6.0^3,10.0^5'9]undecane-8-one-(PCU-8-one, 53) affords a mixture of meso and d,l pinacols (55a and 55b respectively). Acid promoted rearrangement of 55a and 55b conceivably can proceed with migration of C(7)-C(8) and/or C(8)-C(9) to form the corresponding pinacolone(s). In our hands, acid promoted rearrangement of 55a and 55b each proceeds with exclusive migration of C(7)- C(8) bond, thereby affording 58a and 59a respectively. Mechanistic features of this rearrangement are discussed. II. 4,7,1 l-trimethylpentacyclo[6.3.0.0.^2,6.0^3,l0.0^5,9]undecane-exo-4,exo-7-diol (23a) was successfully synthesized. This diol crystallizes in a helical tubuland lattice although its molecular structure does not possess C2 rotational symmetry.
Date: May 1995
Creator: Liu, Zenghui
System: The UNT Digital Library
An Approach Towards the Total Synthesis of Clonostachydiol (open access)

An Approach Towards the Total Synthesis of Clonostachydiol

The syntheses of the unsymmetrical 14-membered bismacrolides have been reviewed. A total synthesis of clonostachydiol, the latest to join this family, has been attempted using trimethylsilyl acetylene as the builiding block and palladium catalyzed reactions for the formation of key bonds. The alkyne groups were introduced by Stille coupling of trimethylstannylethynyltrimethylsilane with an acid chloride for one fragment and by addition of lithiotrimethylsilyl acetylene to an aldehyde for the other. Lactic acid derivatives were chosen as starting materials for both fragments, thus introducing two of the chiral centers. The remaining stereocenters were introduced using stereoselective reductions of ketones.
Date: August 1995
Creator: Maiti, Tushar B. (Tushar Baran)
System: The UNT Digital Library