NMR

Question 1

T/F: the nuclear spins are normally at random orientation but are aligned by a strong external magnetic field

Answer 1

T

Question 2

alpha spin states aligns___ B0

Answer 2

with

Question 3

beta spin states aligns___ B0

Answer 3

against

Question 4

beta spin state has __ energy than alpha

Answer 4

higher

Question 5

when EMR is applied…

Answer 5

nucleus in alpha spin state absorbs energy of photon and flips to beta

Question 6

delta E is dependent upon..

Answer 6

B0

Question 7

if u want a larger delta E,

Answer 7

inc B0

Question 8

if nuclei has significant electron density, overall effect of B0 is __ and is “ ___ “

Answer 8

weakened, shielded

Question 9

if nuclei has less electron density, overall effect of B0 is ___ and is “ __ “

Answer 9

stronger, deshielded

Question 10

T/F: the same type of nuclei in a molecule will flip at diff freq depending on chemical env

Answer 10

T

Question 11

B0 is inverse or proportional to delta E?

Answer 11

proportional

Question 12

T/F: nonequivalent protons have the same chemical shift

Answer 12

F

Question 13

chemical shift equation

Answer 13

(observed shift in Hz/operating freq in Hz) X 10^6

Question 14

downfield = more deshielded or shielded?

Answer 14

deshielded

Question 15

deshielding inc with EN atoms and sp/sp2 character bc

Answer 15

pulls electron density away

Question 16

T/F: deshielding effect is additive

Answer 16

T

Question 17

anisotropy __ the B0 in the regions of the H

Answer 17

reinforces

Question 18

where does a doublet come from?

Answer 18

50% of time a H is more deshielded by a neighbor, other 50% it is more shielded

Question 19

doublet ratio:
triplet ratio:
quartet ratio:

Answer 19

1:1
1:2:1
1:3:3:1

Question 20

spin-spin splitting exceptions

Answer 20

aldehydes, alkenes, rigid bicycles

Question 21

T/F: protons coupled to each other have different J values

Answer 21

false

Question 22

ethyl NMR

Answer 22

2H quartet, 3H triplet

Question 23

isopropyl NMR

Answer 23

1H septet, 6H doublet

Question 24

complex splitting occurs when…

Answer 24

adjacent protons are not chem equiv

Question 25

OH on NMR

Answer 25

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

Question 26

Beneze on NMR: 2 doublets

Answer 26

para, H on 1,2,4,5

Question 27

Benzene on NMR: singlet follows by mess

Answer 27

meta, H on 1,2,3,5

Question 28

Benzene on NMR: a mess

Answer 28

ortho, H on 1,2,3,4

Question 29

CNMR

Answer 29

no spin spin splitting, no integration