Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Orgo Lab > NMR spectroscopy > Flashcards

NMR spectroscopy Flashcards

(67 cards)

Start Studying
1
Q

what does NMR stand for?

A

Nuclear Magnetic Resonance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what does the spinning charge of a nuclei generate?

A

spinning charge generates a magnetic dipole

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what does nuclei possess?

A

nucleic possess charge and can spin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

how are magnetic dipoles characterized?

A

by nuclear magnetic spin quantum number “I”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what are the 3 “cases” or values “I” can be?

A
  1. I = 0
  2. I = 1.2
  3. I > 1/2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what does I = 0 indicate?

A
  • nuclei has a EVEN number of protons and EVEN number of neutrons
  • the nuclei does NOT spin –> does not interact with applied magnetic field
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what are 2 examples of atoms that have magnetic dipoles of I = 0?

A

12C
16O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what does I = 1/2 indicate?

A

nuclei are NMR VISIBLE samples

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

give 2 examples of I = 1/2 nuclei

A

1H
13C (the non-radioactive isotope of C, 1.06% natural abundance)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what are 2 examples of nuclei with magnetic dipole of I > 1/2

A

2H
14N –> difficult to observe

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

more nuclei are aligned with what?

A

more nuclei are aligned with the externally applied magnetic field OR the lower energy alpha-spin state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what direction does the arrow point in for the beta-spin state, the alpha-spin state, and the no field state

A

beta-spin (higher energy): arrow points DOWN
alpha-spin (lower energy): arrow points UP
no field: arrow points in all directions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what happens to the spins of nuclei when a magnetic field is applied?

A

when there is no magnetic field applied, the nuclei spin in ALL directions and there are NO energy differences

when there is a magnetic field applied, the nuclei spins ALIGN WITH or AGAINST the magnetic field (hence the up and down arrows)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

is there an energy difference between the nuclei when no magnetic field is applied?

A

NO, there is no energy difference
–> energy difference increases as magnetic field applied increases though

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is deltaE?

A

the energy difference between alpha and beta-spin states

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is the relationship between applied magnetic field and deltaE?

A

increasing applied magnetic field = increasing deltaE between spin states

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what does it mean when it is said that the “nucleus is in RESONANCE with the applied magnetic field”?

A

when the nucleus ABSORBS ENERGY and flips from the alpha-spin state to the beta-spin state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is the relation between the energy difference deltaE and frequency of the EM spectrum?

A

The difference in energy ΔE between the two spin states corresponds to a frequency in the Radiofrequency region of the EM spectrum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is Planck’s equation?

A

∆E = hν

∆E = γBoh/2π = hν
ν = γBo/2π

γ = gyromagnetic ratio; a constant
that depends on the magnetic
moment of the nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is the gyromagnetic ratio γ?

A

a constant that depends on the magnetic moment of the nucleus
–> it is unique for each nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

which equation describes the condition for resonance?

A

Larmor equation: relates the precession frequency of nuclear spin (w) and the external magnetic field (Bo)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what is the Larmor equation and what does it relate together?

A

Relates the precession frequency of nuclear spin (w) and the external magnetic field (Bo)

Larmor equation: ν = γ Bo /2π or ω = γ Bo
–> where ν= ω/ 2π
ν is in hertz and ω is in radians/second
Γ is the gyromagnetic ratio (unique for each
nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

draw the diagrams/pictures describing nuclei spin and magnetic field

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

describe the x-axis and y-axis of an NMR spectrum

A

x-axis: frequency (increases to the LEFT - different from norm)
Y-AXIS: intensity (increases UPWARD)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
compare deshielded vs shielded nuclei
deshielded nuclei: these protons sense a LARGER effective magnetic field --> come into resonance at a HIGHER frequency shielded nuclei: these protons sense a SMALLER effective magnetic field --> come into resonance at a LOWER frequency
26
relation between shielding and frequency
deshielded = HIGHER frequency = more DOWNFIELD shielded = LOWER frequency = more UPFIELD
27
upfield and downfield relation to frequency
upfield = to the RIGHT and LOWER frequency downfield = to the LEFT and HIGHER frequency
28
describe where CH3Cl and CH4 NMR peaks will look
CH3Cl - electronegative CL withdraws electron density from the C and H atoms --> thus DESHIELDING the C and H atoms --> peak is more DOWNFIELD (to the left, higher frequency)
29
what does deshielding mean?
deshielding = lesser shielding = mose of the applied magnetic field strength is experienced = higher frequency absorbed (downfield)
30
draw the schematic of an NMR spectrometer
31
what are the components of an NMR spectrometer?
- superconducting magnet - NMR console - NMR spectrum - workstation - sample tube
32
describe how an NMR spectrometer works
the sample tube is dissolved in solvent in a thin NMR tube and placed in a magnetic field --> in the NMR probe, the sample is rotated in a magnetic field and irradiated with a short pulse of RF radiation
33
definition of NMR spectrum
a plot of the intensity of an observed NMR signal vs the frequency measured relative to a reference compound (which is typically TMS - tetramethylsilane)
34
what is TMS and its function in NMR spectrum?
TMS - tetramethylsilane the typical reference compound that is used in NMR
35
draw the structure of TMS
36
at what number of x-axis (frequency) is TMS reference peak at?
at 0 on the x-axis
37
what are 3 advantages of using TMS in NMR?
1. TMS has 12 equivalent Hs 2. NMR signal due to protons in TMS appears s a singlet at 0 ppm (way upfield from other signals) 3. it is low-boiling and inert
38
what are 2 common NMR solvents?
CDCl3 - deuterated chloroform --> typically used for nonpolar compounds DMSO-d6 - deuterated dimethyl sulfoxide --> typically used for polar compounds
39
what is the purpose of using solvent for NMR?
the solvent is used to dissolve the compound that you are trying to run the NMR analysis on (in the test tube)
40
what NMR solvent is used for NONPOLAR compounds?
CDCl3 - deuterated chloroform
41
what NMR solvent is used for POLAR compounds?
DMSO-d6 (deuterated dimethyl sulfoxide)
42
draw the structure of deuterated dimethyl sulfoxide (DMSO-d6) and deuterated chloroform CDCl3
43
what is the typical NMR sample prep? (how much compound and solvent)
10-20mg of compound + 0.5-0.6mL of CDCl3 (solvent)
44
what is chemical shift?
aka the position of the peak chemical shift - the frequency different between the resonance observed for the nucleus and the resonance observed for the reference compound (ie. TMS)
45
what is the unit for chemical shift?
ppm
46
degree of unsaturation formula
[2 (# C atoms) + (# N atoms) – (# halogen atoms) - (# H atoms) + 2 ] / 2
47
what does a degree of unsaturation greater than or equal to 4 signify?
DU >= 4 means 3 double bonds + 1 ring --> signifies 1 AROMATIC RING
48
what is the formula for chemical shift?
(sample freq - reference freq) / spectrometer freq
49
what features of a 1H NMR spectrum provides information about a compound's structure?
1. size of/area under the peak (aka integration) = indicative of the NUMBER of IDENTICAL protons in a particular environment 2. # of signals = corresponds to different groups of NON-EQUIVALENT protons 3. position of signals = indicative of the KIND of proton(s) responsible for the signal 4. spin-spin splitting of signals = indicates the # of NEIGHBORING protons (which is calculated using the N+1 rule)
50
what does the size of/ area under the peak of NMR signals indicate?
Size of/ area under the peak ((Integration) of NMR signals = is indicative of the relative number of identical protons in a particular environment
51
what does the number of signals correspond with?
Number of signals = corresponds to different groups of non-equivalent protons
52
what does the position of the signals indicate?
Position of signals = is indicative of the kind of proton/ s responsible for the signal
53
what does the spin-spin splitting of signals indicate?
Spin-spin splitting of signals = indicates the number of neighboring protons = calculated using the (N+1) rule
54
chemically equivalent protons definition
protons in the same environment --> chemically equivalent protons do NOT split each other's signals --> chemically inequivalent protons produce more than one peak
55
what is the area under an NMR signal proportional to?
Area under an NMR signal is proportional to the number of absorbing protons
56
what is the height of each step proportional to?
Height of each step is proportional to the area under the peak which in turn is proportional to the number of absorbing protons
57
number of peaks and their given names?
1 - singlet (s) 2 - doublet (d) 3 - triplet (t) 4 - quartet (q) 5 - quintet 6 - sextet 7 - septet > 7 - multiplet (m)
58
relation between signal multiplicities and their relative intensities of their peaks
singlet - 1 double - 1:1 triplet - 1:2:1 quartet - 1:3:3:1 quintet - 1:4:6:4:1 sextet - 1:5:10:10:5:1 septet - 1:6:15:20:15:6:1
59
when does spin-spin splitting occur?
spin-spin splitting only occurs between NONEQUIVALENT protons on the SAME carbon or ADJACENT carbon
60
what is the (n+1) rule for spin-spin splitting?
a set of "n" nonequivalent protons splits the signal of a neighboring proton into n+1 peaks
61
when is splitting not generally observed?
splitting is not generally observed for protons separated by more than 3 sigma bonds
62
splitting by "n" nuclei of spin quantum number "I" gives ___ how many lines?
Splitting by “n” nuclei of spin quantum number “I” gives (2nI + 1) lines --> For protons where I= ½, this equation results in (n + 1) lines
63
how are coupled nuclei identified?
Coupled nuclei are identified by labels as subscripts after the symbol “J”
64
what does the superscript before the symbol "J" represent?
Superscript before the symbol “J” represents the number of inclusive bonds between the coupled nuclei
65
what is coupling constant J and what units is it in?
Spacing (in Hz) between the lines in the multiplet = Coupling Constant (J) (units Hz) units Hz
66
describe how OH protons are split and what their NMR signal/peak looks like
OH protons are NOT split and they do NOT split the NMR signal of adjacent protons either --> OH proton signal appear as a SINGLET
67
what are the steps for NMR spectroscopy?
Steps 1. Sample is dissolved in solvent in a thick NMR tube and placed in a magnetic field 2. In the NMR probe, the sample is rotated in a magnetic field and irradiated with a short pulse of RF radiation

Orgo Lab (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions