Further synthesis & analysis

• What is chemical shift measured in?

  Parts per million (ppm)
• What is 13C NMR?

  Gives info about how carbon atoms in molecule are arranged (number of carbons & environments they're in).
• What is 1H (proton) NMR?

  Tells us how hydrogen atoms in molecule are arranged (number of hydrogens & environments they're in).
• What is chemical shift?

  NMR spectroscopy measures differences in energy absorbed by nuclei in different environments relative to standard substance (TMS). Difference is called chemical shift.
• Why is TMS the standard substance in NMR?

  Produces single absorption peak away from most other peaks- has chemical shift value of 0. All C & H atoms in identical environments. Chemically inert (doesn't react with sample), non-toxic & volatile (easy to remove from sample).
• What is chromatography?

  Analytical technique used to separate components in a mixture.
• What is the mobile phase?

  Molecules can move-always liquid solvent or gas e.g, ethanol. Moves through or over stationary phase. Liquid solvent in TLC.
• What is the stationary phase?

  Molecules can't move-is a solid or a liquid on solid support. Thin layer of silicon dioxide or aluminium oxide fixed to a glass or metal plate.
• Distance each substance moves depends on what?

  Its solubility in mobile phase & retention in stationary phase. Components more soluble in mobile phase travel further than components more strongly adsorbed to stationary phase.
• Thin layer chromatography steps:

  Pencil line (baseline) near bottom of TLC plate & put small drop of each mixture on line. Allow to dry. Place plate in beaker with small volume solvent (mobile phase) below baseline so samples not dissolved away. Cover beaker with watch glass so solvent doesn't evaporate. Solvent moves up plate & carries substances different distances. Mark solvent front distance. Place plate in fume cupboard. Chromatogram produced.
• Why do you place the TLC plate in a fume cupboard?

  Prevents any toxic or flammable fumes from escaping into the room.
• How do you reveal colourless chemicals?

  Many TLC plates have fluorescent dye added to silica or alumina layer that glows when UV light shines on it. Can also expose chromatogram to iodine vapour (leave plate in sealed jar with iodine crystals). Iodine vapour=locating agent so sticks to chemicals on plate & they'll show as purple spots.