Lecture_6

Lecture_6 - Lecture 6 Thin Layer Chromatography Experiment...

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Lecture 6
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Thin Layer Chromatography Experiment 5 NMR Spectroscopy
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Chromatography Separation of complex mixtures of compounds Name insinuates separation of colored compounds Three types we will discuss: Thin-Layer Chromatography Liquid Chromatography (LC) and High Pressure LC (HPLC) Gas Chromatography
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Concept is based on: Mobile Phase: Liquid or gas that carries compounds through the solid phase Solid Phase: A stationary composite through which the compound and the mobile phase interact
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TLC tells us: Progress of a reaction Rough number of compounds in a mixture Rough indication of purity Relative polarity differences between molecules
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Overview of TLC procedure Making the TLC Chamber
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Let the solvent (mobile phase) equilibrate
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Prepare the TLC plate
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Spot your compound on the TLC
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Develop the TLC plate in the chamber
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Visualize the spots Destructive Staining (KMNO 4 ) Non-Destructive UV-light Iodine (I 2 )
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Calculate R f values (ratio to the front) R f = spot dist divided by solvent dist Must report solvent with R f
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Why do the compound spots move differently?? Answer = Polarity Solid phase (Silica, Alumina, Cellulose) is polar Polar compounds can bind to solid phase by: Hydrogen bonding, van der Walls forces, dipole-dipole “like interacts with like” so polar compounds move slower Non-Polar compounds can bind only by weak vdW These compounds move faster Solvent effects the distance traveled too Compounds move slower in non-polar solvents
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Common Solvent Systems (mobile phase) *You don’t have to use a pure solvent, you can use a mixture to cater to the polarity you want Hexanes (non-polar) Dichloromethane (non-polar) Ether (moderately polar) Ethyl acetate (moderately polar) Acetone (polar) Water not advised because it dissolves silica gel Most common system is a ratio of hexanes/ ethyl acetate
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So, TLC tell us what again?? If the reaction is done or not
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Lecture_6 - Lecture 6 Thin Layer Chromatography Experiment...

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