NMR Spectrometry Flashcards
Number of signals tells…
how many distinct environments of the given atom
Chemical shift in PPM tells…
type of environment; shielding from electrons (closer to EWG = less e shielding so shift downfield)
Decrease in shielding (deshielded) = experience greater effective magnetic field = increase in energy = increase in frequency absorbed = higher frequency signal = shift downfield to left
Integration Value tells…
intensity of the integration value provides the relative number of atoms making that signal
Coupling pattern tells…
splitting of the same peak tells us the number of the same type of atoms in close proximity in nonequivalent environments
coupling constant value
substitution pattern or stereochemistry based on size
to determine purity or relative abundance…
compare the integration of two signals in separate molecules
Leaning
different signals from the same molecule on the NMR spec can lean toward each other / \ .
Also called “roofing”
point of reference on an H-NMR Spec
TMS
(central Si bonded to 4 methyl groups)
Set at 0 ppm on an H-NMR Spec.
NMR Spectroscopy - Summary
1H-NMR and 13C-NMR spectra are very useful for structural determination of organic molecules.
NMR techniques are based upon the interaction between radio frequency light and the
magnetic properties of nuclei in a molecule.
1H-NMR and 13C-NMR spectra use TMS as a 0 ppm reference.
Important information is found in the # of signals, chemical shift (ppm), integration
value, coupling pattern (multiplicity), and coupling constants (Hz).
For 1st order 1H-NMR spectra, the n+1 rule is useful for interpreting coupling patterns.
The size of the coupling constants can be used to interpret stereochemical and
regiochemical relationships of protons.
Coupling constant j (hz)
Distance between peaks in coupling patterns
