NMR Flashcards
Understand NMR
Xrays are scattered by atoms
we can measure the scattering pattern to tell us abput bond length and angles
Radio waves make nuclei resonate
resonant frequencies tell us about the symmetry, connectivity of the hydrocarbon skeleton
IR waves make bonds vibrate
by plotting charts of absorption we can determine the functional groups in the molecule
What does NMR do
it can tell the different proton environmentsand distinguish between the different protons
what do the chemical shifts measure
the amount of shielding or deshileding around the proton
H atoms bonded to saturated carbons are where on the chemical shift?
right hand side, upfield, lower numbers, more shielded
H atoms bonded to electronegative atoms are where on the chemical shift?
downfield, to the left, higher numbers, deshielded
What is coupling?
protons interacting magnetically and can reveal the connectivity of the structure.
Where will CH3, CH2 and CH resonate?
CH3 are completely saturated and so resonate around 0.9. CH2 have 2 substituent atoms and thus resonate around 1.3 and CH at about 1.7
The intensity of the signal is…
generally proportion to th number of protons coming into resonance at the frequency of the signal
The integration of the signal is…
the area under the absorption peak that is proportional to the number of protons being detected
The number of hydrogens on each peak represtented by the integration should…
add up to the total number of protons in the molecule
NMR and the inductive effect
The more alkyl groups you add onto a carbon, then the further downfield the molecule will be (downfield means a higher value)
Ainstropy of chemical bonds
chemical bonds are also regions of high electron density and if the field is sronger in one direction then the bond is ainstropic
Pi bonds and chemical shifts
pi bonds are especially effective in influencing the chemical shift of nearby atoms relative to their saturated counterparts
