Analytical techniques
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what type of radiation does NMR use?
radiowaves
what is the standard reference used in NMR?
tetramethylsilane (CH3)4Si (has a chemical shift of 0 ppm)
what does NMR stand for?
nuclear magnetic resonance
deuterated solvents
solvents where ¹H atoms have been replaced by ²H atoms (deuterium, D) to ensure that all signals are from the compound being tested and not the solvent
common solvent used in NMR spectroscopy
CDCl3
what peaks does CDCl3 show?
• no peaks in proton NMR (D is used) • peak in carbon-13 NMR which the computer usually filters out before displaying the spectrum
proton exchange
• proton NMR spectrum run as normal • small volume of deuterium oxide, D2O, is added to the mixture and shaken under second spectrum is run
what protons does deuterium replace?
protons in OH and NH groups (these peaks will disappear)
molecular ion peak
peak with the highest m/z value which gives the Mr of the compound
molecular ion
compound –> e- + [molecular ion]+
M+1 peak
small peak one unit after the M+ peak because a small amount of carbon-13 is present (adds an Mr of 1)
fragmentation
molecular ions break down into smaller pieces consisting of a fragment ion and a radical