Call number: LD2668 .T4 1961 R68

published_or_final_version / Chemistry / Master / Master of Science

Of the interactions utilized in the separation of chemical species, the reversible covalent bond is the strongest and most selective. In order to exploit the selectivity of this interaction, an understanding of the effects of several factors on the formation of the covalent bond have been studied. Covalent chromatography is most useful in solid phase extraction. The strength of the covalent bond will allow for high distribution coefficients needed to quantitatively retain chemical species. The selectivity of the covalent interaction allows for the retention of a specific compound or class of compounds. Under conditions where the covalent bond is no longer formed or will break, a low distribution coefficient is possible, and the compounds may be eluted from the sorbent in a small volume allowing for preconcentration. The sorbent consists of three parts, the active functionality capable of forming reversible covalent bonds, the solid support and the spacer arm that tethers the active functionality to the support. Silica supports demonstrate several advantages over organic supports. However, silica supports have been limited by the activity of the residual silanols and the use of hydrophobic spacer arms. This research describes the preparation and characterization of a modification method for silica with a hydrophilic spacer arm that restricts the sample from the residual silanols. Immobilized phenylboronic acid (PBA) interacts with compounds containing polar functionalities in the correct configuration, but this interaction is dependent on the local environment. Controlling the local environment allows for the control of the interaction provided the effects are understood. Diagnostic chromatography was used to determine the effects of the solvent strength, ionic strength, pH and composition of the mobile phase and the effects of the spacer arm on the interactions of PBA with several compounds. Three phases selective for thiols were also characterized. Thiopyridone attached to mercaptopropyl bonded silica through a disulfide linkage, is used for isolation and detection. Immobilized phenylmercury was utilized for the extraction of thiol containing species while immobilized phenylarsonous acid selectively extracts dithiol compounds. A unique and powerful means of separation of monothiol from dithiol compounds has been demonstrated.

This dissertation describes the experimental study of the electronic-structural relationships of selected mononuclear transition-metal sulfur dioxide, cyclopentadienyl and carbonyl complexes and the application of the information gained from these to the study of quadruply-bonded dimetallic complexes. These pertinent observations result from the application of photoelectron spectroscopy (p.e.s.) as a probe into the bonding, charge-distribution and excited state effects which contribute to the specifics of the ground and excited state molecular structures. The first part of this discussion centers around a specific study of the exemplary bonding probe, SO₂, with the well characterized ArM(CO)₂ metal fragment, where Ar = Bz and Cp and M = Cr, Mn and Re. A comparison of the ionization information with the structural details and molecular orbital calculations reveals not only the surprising coordinating similarity of SO₂ and CO in these complexes, but also the electronic origin for the counter-intuitive SO₂ bonding configuration. This work then moves to a more dramatic example of electronic control of ground state molecular structure; the crystallographically determined distortion of the coordinated Cp ring in Cp*Rh(CO)₂. The electronic origin of this distortion is graphically shown with the aid of two and three dimensional experimental and theoretical electron density maps. The structural effects of removing bonding electrons from quadruply-bonded dimetallic complexes is then investigated. This study incorporates the use of high-resolution p.e.s. for the novel observations of metal-metal vibrational structure in the predominantly metal ionizations providing direct information of the bonding influence of specific metal electrons. Particular attention is focused on the delta-ionization process of MO₂(O₂CCH₃)₄. The final chapter presents a comprehensive study of the valence and core ionizations of the series of quadruply-bonded M₂(X₂CR)₄ complexes, where M₂ = Cr₂, Mo₂, MoW, and W₂, X = O and S, and R = H, CH₃, CD₃, CF₃, CH₂CH₃, CH₂CH₂CH₃ and C(CH₃)₃. The changes in the electronic structure in both the ground and excited states of these molecules is presented and, where appropriate, compared to structural changes. The study of this series not only demonstrates how p.e.s. can be used to monitor the electronic effects of specific chemical modifications, but also reveals surprising excited state features related to facile charge-reorganization processes.

Call number: LD2668 .T4 1958 D63 / Master of Science

Digitized by Kansas Correctional Industries

Guo-cong Guo. / "June 1999." / Thesis (Ph.D.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

A long-standing research interest of the Leighton group has been the utilization of strained silanes in the rapid and efficient synthesis of polyketides. Recently, we have been interested in how the effects of strain might manifest itself in the conductance and functionality of silicon-based molecular junctions. As electronic components continue to miniaturize to the point where transistor size and structure begin to resemble small molecules, understanding the principles that guide charge transport in single molecule junctions will be crucial. Herein, we describe our studies on a series of single molecule junctions formed by strained silicon wires. We demonstrate that high conductance pathways are accessed for the cis diastereomers of conformationally locked 1,2-disilaacenaphthenes via a bipodal binding motif which provides a stable electrical contact between the Si—Si bond and the gold electrodes. We then elucidate the mechanism of voltage-induced breakdown in silicon-based single molecule junctions. We show that the naphthalene bridge provides a parallel conductance pathway to the silicon backbone, altering bond rupture behavior of the Si—Si bond. We further investigate the bond rupture mechanism through DFT and molecular dynamics calculations and conclude that breakdown occurs by the excitation of vibrational modes in the molecular junction by tunneling electrons, leading to homolytic Si—Si bond rupture.

*Please refer to dissertation for diagrams. / Part 1 describes the selective C(alpha)-(beta) bonds cleavage of a series of aliphatic ethers (RCH2OCH2R: R = Et, Pr, Bu, iBu and pentyl) by RhII(tmp) using PPh3 as the promoting ligand to give Rh(tmp)-alkyls bearing the C(beta)-substituent in 13-40% yields at 24°C. The rate and the yields of Rh(tmp)-alkyls decreased with increasing steric hindrance of ethers. Addition of bases such as KOtBu, CsOH.H2O and KOH as well as H2O further promoted the product yields of the reactions with n-butyl ether to 56-62%. The reaction between RhII(tmp) and the cyclic ether, oxepane, at 24°C for 1 day gave Rh(tmp)(CH2)5OCHO in 17% yield suggesting that Rh(tmp)OH is the key intermediate in the C-C cleavage step and presumably generated via the PPh3-, H2O-, and OH --assisted disproportionation of RhII(tmp).* / Secondly, the reductive dehydrogenation of Rh(tmp)H to RhII(tmp) was also observed. Rh(tmp)H reacted with KOH in benzene-d6 at 100°C for 1 hour to give RhII(tmp) in 30% yield. [Rh I(tmp)]- is proposed to form initially via the deprotonation of Rh(tmp)H with KOH and then reacts with the unreacted Rh(tmp)H to give Rh II(tmp) via electron transfer. Thirdly, the hydroxide-induced disproportionation of RhII(tmp) to RhIII(tmp)OH and [Rh I(tmp)]- has also been proposed.* / The objective of this thesis focuses on studies of selective, base-promoted aliphatic carbon(alpha)-carbon(beta) bond activation (CCA) of ethers with rhodium(II) and rhodium(III) meso-tetramesitylporphyrin complexes (Rh II(tmp) and Rh(tmp)I). The roles of potassium hydroxide in promoting the interconversions of rhodium porphyrin species (RhII(tmp), Rh(tmp)I, Rh(tmp)OH and Rh(tmp)H) will also be discussed. / Lai, Tsz Ho. / Adviser: Kin Shing Chan. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 161-172). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

by Zhang Lirong. / "September 2006." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese.