NMR

NMR

1. Nuclear Magnetic Resonance

   • In organic chemistry, H+ NMR and carbon-13 NMR are useful for general purpose techniques.
   • Requirements
     • Strong magnetic field applied using an electromagnet
     • low-energy radio-frequency radiation.
   • It is measured using solutions of the substance. It is important that solvent don't contain any simple H atoms- confusing peaks
     • CDCL3
       • Deuterium, D, is an isotope of the hydrogen. 1 proton and 1 neutron
         • Even number of nucleons so no signal is produced

2. Chemical Shift,(S) is the place in an NMR spectrum at which nucleus absorb energy.

   • calibrated using the delta scale and measured in ppm.
   • measured relative to TMS (tetramethylsilane)
     • Some NMR spectra show the peak due to TMS (at zero)
     • TMS have 12 equivalent protons and gives rise to single, sharp NMR signal. 1 environment
       • TMS is chemically unreactive and volatile so it can be easily removed.

3. Carbon-13 NMR

   • Has odd number of nucleons so results in a magnetic spin
   • is sensitive to nuclear sheilding and gives large range of S values, 0-230ppm
   • the number of different carbon environment (from the no. of peaks)
   • the types of carbon environment- chemical shifts
     • Aromatic Compounds
       • Symmetrical

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