NMR Flashcards
(29 cards)
T/F: the nuclear spins are normally at random orientation but are aligned by a strong external magnetic field
T
alpha spin states aligns___ B0
with
beta spin states aligns___ B0
against
beta spin state has __ energy than alpha
higher
when EMR is applied…
nucleus in alpha spin state absorbs energy of photon and flips to beta
delta E is dependent upon..
B0
if u want a larger delta E,
inc B0
if nuclei has significant electron density, overall effect of B0 is __ and is “ ___ “
weakened, shielded
if nuclei has less electron density, overall effect of B0 is ___ and is “ __ “
stronger, deshielded
T/F: the same type of nuclei in a molecule will flip at diff freq depending on chemical env
T
B0 is inverse or proportional to delta E?
proportional
T/F: nonequivalent protons have the same chemical shift
F
chemical shift equation
(observed shift in Hz/operating freq in Hz) X 10^6
downfield = more deshielded or shielded?
deshielded
deshielding inc with EN atoms and sp/sp2 character bc
pulls electron density away
T/F: deshielding effect is additive
T
anisotropy __ the B0 in the regions of the H
reinforces
where does a doublet come from?
50% of time a H is more deshielded by a neighbor, other 50% it is more shielded
doublet ratio:
triplet ratio:
quartet ratio:
1:1
1:2:1
1:3:3:1
spin-spin splitting exceptions
aldehydes, alkenes, rigid bicycles
T/F: protons coupled to each other have different J values
false
ethyl NMR
2H quartet, 3H triplet
isopropyl NMR
1H septet, 6H doublet
complex splitting occurs when…
adjacent protons are not chem equiv
