NMR Flashcards
NMR is added to as an analytical technique
mass spectrometry and infared spectrometry
NMR stands for
nuclear magnetic resonance
NMR gives information about
the posistion of 13C or 1H atoms in a molecule
does 13C NMR or 1H NMR simpler spectra
13C NMR
why is NMR such a powerful technique
it is easy to obtain spectrum
only small amount of sample necessary
non-destructive so sample can be tested can be used again
what can you interpret from 13C NMR
number of peaks = number of carbon environments
location (ie chemical shift) of peaks = type of carbon environment
how to determine number of carbon environments
each carbon which has a different amount of electron density around it is said to be a different ‘environment’
the electron density around a carbon is determined by its proximity to other carbons, electronegative atoms or functional groups.
Looking for lines of symmetry in a molecule can help identity which atoms are in same and which are in different ‘environments’
chemical shift depends on
molecular environment
reasons why TMS is used as a standard
it generates one sharp peak
unreactive so wont affect sample being anylaysed
highly volatile(turns liquid to gas very easily)
peaks always found on the far right of the spectrum
what does TMS stand for
tetra methyl silane
4 things to interpret in a 1H NMR spectrum
number of peaks = number of proton environments
location of peak (chemical shift)= type of proton environment
area under each peak (the intergration ratio) = number of protons in each environment
the splitting(coupling) = number of protons in the adjacent environments
in NMR the closer to an electronegaitve atom
the higher the chemical shift for that carbon
splliting =
n + 1
where n is the number of protons on adjacent carbon
so singlet means no H’s adjacent and doublet means 1 adjacent
NMR - table headings to fill in for each peak in spectrum to summarise all info needed
chem shift, splitting pattern, no. adjacent H’s, intergration ratio, environemnt, structures
1H NMR spectra are obtained using
samples dissolved in deuterated solvents (any solvent where H has been replaced by D can be used like CDCl3 for polar samples and C6D6 for non polar sample) or CCl4
