NMR Flashcards
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
OH on NMR
may or may not come up bc of proton exchange so not in one chemical env all the time, but would be bs 0.5-5
Beneze on NMR: 2 doublets
para, H on 1,2,4,5
Benzene on NMR: singlet follows by mess
meta, H on 1,2,3,5
Benzene on NMR: a mess
ortho, H on 1,2,3,4
CNMR
no spin spin splitting, no integration
