Chemistry - Instrumental Analysis

• What is nuclear magnetic resonance used for

  to determine the structure of molecules
• how is the magnetic field affected in NMR

  effected by different functional groups
• what does the number of peaks on the NMR spectrum represent

  how many carbon environments are in a molecule
• why is TMS used as a standard - NMR

  chemically unreactive

  has 12 protons and 1 carbon so gives a sharp and easily measured peak on both 13-C and 1-H

  heavily shielded nuclei - rarely peaks below

  volitle and easily removed from sample
• how does symmetrical and non-symmetrical molecules effect NMR

  non-symmetrical - need to count all carbons in molecules ( most likely different carbons )

  symmetrical - may have more than 1 of the same type of carbon bond - but must be included in the spectrum drawing
• what is a mass spectrometer used for

  predict the chemical structure if a compound.

  forms a positive ion on the mass spectrum diagram
• what is the M+

  the ion of the total molecules - peak furthest to the right

  total ions does fragment ( peaks to the left)
• what is the m/z - mass spec

  relative molecular mass of an ion

  m/z of 29 = CH3CH2

  m/z of Mr-15 = lost CH3
• what is not recorded on mass spectrometry

  radicals