CHS1440Ch09

CHS1440Ch09 - Chapter 9 Molecular Geometries and Bonding...

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Molecular Geometries and Bonding Chapter 9 Molecular Geometries and Bonding Theories
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Molecular Geometries and Bonding Taxol (Paclitaxel) Julius Caesar mentioned in his “Gallic Wars” that Catuvolcus, a cheiftain of the Eburones, committed suicide by taking extracts from the yew tree Other more recent accounts report uses such as extracts as poison or as a cancer-healing folk medicine In 1962, A.Barclay collected bark from Taxus brevifolia, the Pacific Yew tree, as part of a national project aimed at the discovery of new anticancer agents in 1971, the molecular structure of taxol was reported based on an X-ray crytallographic analysis In 1979, Horwitz reports the interaction of taxol with microtubules 1983: Research triangle sponsors phase I clinical trials of paclitaxel 1985: NCI begins phase II trials of Paclitaxel 1989: NCI issues an open invitation to pharmaceutical companies to compete for the right to be its commercial development partner for the drug 1991: Bristol – Myers Squibb Company is selected by NCI to be the commercial partner in developing Taxol® injections
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Molecular Geometries and Bonding
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Molecular Geometries and Bonding Molecular Shapes • The shape of a molecule plays an important role in its reactivity. • By noting the number of bonding and nonbonding electron pairs we can easily predict the shape of the molecule.
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Molecular Geometries and Bonding What Determines the Shape of a Molecule? • Simply put, electron pairs, whether they be bonding or nonbonding, repel each other. • By assuming the electron pairs are placed as far as possible from each other, we can predict the shape of the molecule.
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Molecular Geometries and Bonding Electron Domains • We can refer to the electron pairs as electron domains . • In a double or triple bond, all electrons shared between those two atoms are on the same side of the central atom; therefore, they count as one electron domain. • This molecule has four electron domains.
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Molecular Geometries and Bonding Valence Shell Electron Pair Repulsion Theory (VSEPR) “The best arrangement of a given number of electron domains is the one that minimizes the repulsions among them.”
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Molecular Geometries and Bonding Electron-Domain Geometries These are the electron-domain geometries for two through six electron domains around a central atom.
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Molecular Geometries and Bonding Electron-Domain Geometries • All one must do is count the number of electron domains in the Lewis structure. • The geometry will be that which corresponds to that number of electron domains.
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Molecular Geometries and Bonding Molecular Geometries • The electron-domain geometry is often not the shape of the molecule, however. • The molecular geometry is that defined by the positions of only the atoms in the molecules, not the nonbonding pairs.
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Molecular Geometries and Bonding Molecular Geometries Within each electron domain, then, there might be more than one molecular geometry.
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Molecular Geometries and Bonding Linear Electron Domain
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CHS1440Ch09 - Chapter 9 Molecular Geometries and Bonding...

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