State College, NY, United States
State College, NY, United States

Time filter

Source Type

A series of bonded phases were prepared by the chemical modification of silica using the surface polymerization of trifunctional and difunctional ligands, and the structural morphology was characterized by solid-state nuclear magnetic resonance (NMR) spectroscopy using cross-polarization and magic angle spinning (CP/MAS). Mixed-phase surfaces were prepared using mixtures of trifunctional long-chain (C18) ligands with trifunctional and difunctional short-chain (C1) ligands, and these surfaces were compared to the corresponding single-phase surfaces consisting of only long- or short-chain ligands. For both types of mixed-phase surfaces, the incorporation of short chains increases the overall ligand density, the density of long chains, and the degree of cross-linking between ligands compared to that of the single-phase surface consisting exclusively of long chains. When the percentage of long-chain ligands in the mixture is high, a horizontally polymerized monolayer of chains is formed on the silica surface for both trifunctional and difunctional short chains. However, essentially all of the long chains adopt a trans conformation when trifunctional short chains are used, and a significant number of gauche defects are observed for the long chains when mixed with difunctional short chains. Furthermore, the ligands on the mixed-phase surface are more rigid when the short chains are trifunctional. When the percentage of trifunctional short chains is increased, some vertical polymerization occurs, caused by the molecular stacking of the highly reactive short chains near the surface. However, this does not preclude cross-linking between the ligands necessary to seal the surface, and the degree of cross-linking is quite high, suggesting that the short chains cross-link both vertically, away from the surface, and horizontally, across the surface. No such vertical polymerization is observed for the bulkier difunctional short chains. For both trifunctional and difunctional short chains, the surface chains are more mobile, with a greater number of gauche conformations among the long chains when the percentage of short-chain ligands in the reaction mixture is increased. © 2013 American Chemical Society.


Pavel J.T.,Oswego State University | Hyde E.C.,Oswego State University | Bruch M.D.,Oswego State University
Journal of Chemical Education | Year: 2012

This experiment introduced general chemistry students to the basic concepts of organic structures and to the power of spectroscopic methods for structure determination. Students employed a combination of IR and NMR spectroscopy to perform de novo structure determination of unknown alcohols, without being provided with a list of possible structures. Students used IR spectra to identify functional groups present, then constructed trial structures and predicted the NMR spectrum, modifying the structure until agreement was obtained. The structure was confirmed by comparison of boiling point and density data, measured in triplicate, to literature values, and the precision and accuracy of student measurements was critically evaluated. © 2012 The American Chemical Society and Division of Chemical Education, Inc.

Loading Oswego State University collaborators
Loading Oswego State University collaborators