Orientation and chemistry of alkoxides on copper(111)
Street, Shane Clark
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Permalink
https://hdl.handle.net/2142/19955
Description
Title
Orientation and chemistry of alkoxides on copper(111)
Author(s)
Street, Shane Clark
Issue Date
1995
Doctoral Committee Chair(s)
Nuzzo, Ralph G.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
Surface analytical techniques have been used to study the interaction of straight-chain alcohols with a preoxidized single-crystal Cu(111) surface under ultra-high vacuum conditions. The adsorbed alcohols deprotonate to form stable alkoxides chemisorbed to the surface. These alkoxides decompose at elevated temperatures by $\beta$-hydride elimination, desorbing as aldehydes. The influence of deuterium isotope labelling, selective fluorination, and chain length on this mechanism has been studied. Temperature Programmed Reaction (TPR) spectra for the reactions of ethoxides and 1-propoxides and their selectively deuterated counterparts reveal both primary kinetic isotope effects and measurable secondary isotope effects.
Fourier Transform Infrared Reflection Absorption Spectra (FT-IRAS) have been obtained for ethoxide, selectively fluorinated and deuterated ethoxides, 1-propoxide and selectively deuterated 1-propoxides, at saturation coverages on the Cu(111) surface. Quantitative measurements of the absorption intensities of the absorbed alkoxides and the randomly oriented corresponding alcohols allowed determination of the orientation of the adsorbed ethoxide and trifluoroethoxide. Ethoxide on the Cu(111) surface has the C-C bond tilted 70 $\pm$ 2$\sp\circ$ from the surface normal while in trifluoroethoxide the C-C bond is oriented 50 $\pm$ 5$\sp\circ$ from the surface normal. In both species the plane of the molecule defined by the C-C-O atoms is tilted towards the surface. This tilt between the plane of the molecule and the plane of the surface normal is 17 $\pm$ 2$\sp\circ$ for ethoxide and 20 $\pm$ 11$\sp\circ$ for trifluoroethoxide. The FT-IRAS spectra of the 1-propoxides have been compared to the reflection infrared spectra of self-assembled monolayers containing long alkyl chains. The spectra show evidence for both crystalline-like packing and conformational disorder in the adlayer, suggesting the presence of both ordered and disordered domains of the alkoxides on the Cu(111) surface. Finally, the FT-IRAS spectra of propene and a set of fluorinated propenes have been obtained. These physisorbed molecules are shown to lie with their molecular C-C=C planes parallel to the metal surface.
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