Browsing by Subject "Chemistry, Organic"
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Item Efforts toward the total synthesis of 7-deoxyzaragozic acic A and galtamycinone(2002-05) Escobar, Maya; Martin, Stephen F.Studies toward the total synthesis of 7-deoxyzaragozic acid A (2.56) were intended to build upon the completion of the synthesis of 6,7-dideoxysqualestatin H5 (2.47) that featured the stereoselective intramolecular vinylogous aldol reaction of the furoic ester 2.23a to give 2.26 or its trimethylsilyl ether derivative 2.30, which possess the requisite absolute stereochemistry at C(3)-C(5) of the zaragozic acids. The improvement of the synthesis of a-ketoester 2.25a from an 18% overall yield to 28% while also reducing the amount of chromatography needed for the intermediates was accomplished. Efforts toward the elaboration of butenolide 2.30 revealed that oxygen nucleophiles were incompatible with the system, however this issue was effectively addressed by the use of a silane nucleophile, which was added in a Michael fashion to the butenolide 2.30 with the correct stereochemistry. While this was proof of concept for elaboration of the core system, it was unfortunate that the silane 2.71 could not be converted to the desired oxygen functionality. Additionally, efforts were made to incorporate functionality at C-6 from the beginning of the synthesis in the form of a brominated furoic acid derivative 2.90, however the Lewis acid mediated cyclization of this species was low yielding with unknown stereochemical outcome. In addition to the studies toward the total synthesis of 7-deoxyzaragozic acid A, the total synthesis of galtamycinone (3.2) was also investigated. Although the total synthesis could not be completed, methodologies have been developed that were used to synthesize C-aryl glycosides 3.80 and 3.85 which established these methods as a viable alternative to the O C glycoside rearrangement.Item Surface processes : ruthenium film growth, silicon nanocrystal synthesis, and methylene partial oxidation(2001-08) Smith, Kristen Colleen; White, John M.This dissertation focuses on advancements of several surface processes. First, a generalizable method to screen organometallic molecules suitable for chemical vapor deposition (CVD) is described. Of four candidates, one precursor, [Ru(C5H5)(CO)2]2, was proven suitable for CVD. Using O2 as a reaction gas, pure, conformal, conductive ruthenium films were produced on patterned Si3N4 and flat (Ba,Sr)TiO3 substrates. Without O2, significant amounts of carbon were incorporated into the film. X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and four point probe techniques were used to analyze the effect of O2 and substrate temperature on the deposition of ruthenium films. Next, the nucleation and growth of Si nanocrystals on SiO2 and Si3N4 is discussed. The effect of substrate temperature, reactive gas composition, and viii surface chemistry is discussed. The thrust is to understand the impact of the surface and gas phase chemistries on the nucleation and growth characteristics of Si nanocrystals. Then, the oxidation of Si nanocrystals is reported. Even though the oxidation of planar Si is well understood, the confined geometry of nanocrystals affects the oxidation process significantly. In this report, Si nanocrystals are oxidized in NO and O2 ambients at temperatures ranging from 650 to 1050 o C. The extent of nanocrystal oxidation is analyzed using X-ray photoelectron spectroscopy, transmission electron microscopy and energy filtering transmission electron microscopy techniques. NO oxidation leads to highly self-limited growth; O2 oxidation at 1050 o C leads to complete nanocrystal oxidation. At 850 o C, in O2 atmospheres there is positive evidence for self-limiting oxidation. Sequentially oxidizing nanocyrstals, first in NO and then in O2, has been shown to lead to very controlled oxide shell thickness. Finally, the reactions of CH2I2 on clean and O(a) precovered Ag(111) have been examined using temperature programmed desorption and reflection adsorption infrared spectroscopy. On clean Ag(111), CH2I2 dissociates to CH2(a) and I(a). CH2(a) groups recombine in a reaction limited process to form C2H4(g). On oxygen precovered Ag(111), the extent of C2H4 formation decreases and CH2O evolves in a reaction limited process. The formation of gas phase CO2 suggests that the formation of formate is a secondary reaction product