Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

ochem2 > spectroscopy > Flashcards

spectroscopy Flashcards

1
Q

What is spectroscopy?

A

When molecules absorb different energies of electromagnetic radiation (light) results in different types of motions in molecules

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

What does spectroscopy allow for?

A

To measure the energy differences of state energies in an allowed system via frequencies by determining the amount of energy absorbed

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

What is the main characteristic of energy states? In what direction to molecules go once absorbed?

A

They are quantized or set, like stairs. Go from lower to higher energy states by absorbing energy.

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

What is the equation for the difference in energy states? What is the relationship between change in energy and frequency?

A

Planks constants(frequency). Difference in energy is proportional to frequency

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

What is resonance in terms of spectroscopy?

A

The energy match between radiant light and the difference of energy between the two different quantized energy states that brings about the transition between the states

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Infrared light changes what state?

A

Vibrational

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

UV/visible light changes what state?

A

Electronic

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

Radio frequency light changes what state?

A

Spin states of an atomic molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
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
10
Q

What energy absorption is measured in NMR?

A

Energy absorption corresponds to energy difference between two spin states of a nucleus in a magnetic field

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

What nuclei are most commonly observed in NMR?

A

Proton and C13

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

What direction of spin and magnetic moment results in alpha spin?

A

Counter clockwise spin and upwards magnetic moment

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

What is the relative energy level of alpha spin and its relation to external magnetic field (Bo)?

A

Lower energy (more stable)
Aligned with Bo

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

What direction of spin and magnetic moment result in beta spins?

A

Clockwise spin and downward magnetic moment

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

What is the relative energy and alignment of beta spins to Bo?

A

Higher energy (less stability)
Aligned against Bo

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

What is the direction of spins in free space?

A

They orient in any direction

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

What is the orientation of spins when influenced by an external magnetic field?

A

Spins will go towards or against the Bo, a majority will be alpha, meaning they go along the same plane as the Bo.

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

What is the relative energies of alpha and beta spins in free space compared to when Bo is present?

A

They have equal energy in free space but when external magnetic field is present (Bo) then alpha is lower energy

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

What is the difference in energy levels of alpha and beta spins dependent on?

A

Dependent on the external magnetic field (Bo) energy level

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

Can alpha spin nuclei be changed to beta? T/F

A

True, through the nrg absorption it can change spin state. Go from lower to higher energy level

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

The lower the strength of Bo the larger the difference in energy levels of alpha and beta states? T/F

A

False. Frequency and magnetic field are proportional. Increase in Bo= increase frequency = increase difference in energy level

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

What is the equation to determine frequency?

A

Frequency= (gamma- magnetogyric ratio nucleus constant)(B-magnetic field @nucleus)/2pi

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

How do we distinguish nuclei when using NMR?

A

They all exist in different chemical environments

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

What are the forms of electronic charge clouds? Where are they located? What is its function?

A

Electronic charge clouds are surrounding each nucleus and are found in the form of bonds to other atoms and atom spatial awareness. Functions to shield from magnetic field.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Does the magnetic field affect electronic motion? T/F

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the result of electronic motion on magnetic field?

A

Electronic motion creates its own magnetic field locally that opposes the applied magnetic field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the equation to determine the magnetic field felt at the nucleus?

A

B (magnetic field felt at nucleus)= Bo-B’( induced e cloud)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is the function of the electronic cloud?

A

To shield the nucleus from the external electronic magnetic field (Bo)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Is the magnetic field felt at all nuclei the same?

A

No, it is different due to the difference in their chemical environments and will have different resonances (types of light energy they can absorb)

30
Q

What is deshielded? What other term is it relative to?

A

Smaller electronic clouds meaning they feel more of the Bo and greater velocity and greater difference in energy levels. Relative to downfield

31
Q

What is shielded and what term is it relative to?

A

Greater electronic cloud so it feels less of the Bo and therefore less frequency and difference in energy. Relative to upfield

32
Q

What is chemical shift?

A

When resonance frequencies are compared relative to a standard (TMS)

33
Q

What is the standard used in chemical shift calculations? What is its frequncy?

A

TMS (tetramethylsilane) is the standard and has a frequency of 0ppm.

34
Q

What is the equation to determine chemical shift?

A

(Velocity of sample- Velocity of TMS / Velocity of instrument)(10^6ppm)

35
Q

What C isotope are we observing in C NMR?

A

13C

36
Q

What is the spin quantum of 13C NMR?

A

1/2

37
Q

What is the range of 13C NMR? Is it simple? What is the signal like?

A

0-220ppm, much simpler compared to proton NMR, weaker signal

38
Q

What are the three differences of 13C to 1H NMR?

A
  1. Single, well defined peak per type of C
  2. Decoupled- no splitting is observed
  3. Intensity- not useful to determine quantity
39
Q

What are the three considerations of chemical shifts?

A
  1. EN of attached atoms
  2. Degree of substitution
  3. Hybridization
40
Q

How does electronegativity affect chemical shift of c?

A

More electronegative atoms pull electron density from the cloud around the C in questions and DESHIELDED it so more exposed to Bo so larger shift.

41
Q

How does degree of substitution affect chemical shift of C?

A

Increased substitution allows for more EN atoms to withdraw electron density from C resulting in DESHIELDING. More substitution = higher chemical shift and frequency

42
Q

What are two considerations when looking at 13C NMR?

A

Chemical equivalence and symmetry

43
Q

How does hybridization affect shielding and chemical shift?

A

Shielding: sp3>sp>sp2
Chemical shift: sp2>sp>sp3

44
Q

What is the main characteristic of peak intensity of 13C NMR?

A

Variable, quaternary C have low peak intensity

45
Q

What is the range of 1H NMR?

A

0-12ppm

46
Q

What is integration in terms of 1H NMR?

A

The measure of relative peak areas giving the relative number of H’s contributing to each signal

47
Q

What is multiplicity when it comes to 1H NMR?

A

Signal splitting, tells the number of vicinal H’s due to the spin-spin coupling

48
Q

What are the 8 multiplicity values/names?

A

Singlet s- 1
Doublet d- 2
Triplet t- 3
Quartet q- 4
Pentent - 5
Sextet- 6
Septet-7
Multiple m- many, indecipherable

49
Q

What is the equation for multiplicity?

A

N+1 (n=of equivalent vicinal protons)

50
Q

What is the coupling constant?

A

The amount of space between downfield and upfield peaks

51
Q

What is the special condition of H in equivalent environments?

A

They do NOT split each others signal, even if they are vicinal

52
Q

How do you determine peak intensity?

A

By looking at the percent influence of varying spin states couplings

53
Q

How many peaks and peak intensity is in a singlet?

A

1 peak, 1 intensity

54
Q

How many peaks and peak intensity is in a doublet?

A

2 peaks, 1:1 ratio

55
Q

How many peaks and peak intensity is in a triplet?

A

3, 1:2:1 ratio

56
Q

How many peaks and peak intensity is in a quartet?

A

4 peaks, 1:3:3:1

57
Q

How many peaks and peak intensity is in a pentet?

A

5 peaks, 1:4:6:4:1

58
Q

How many peaks and peak intensity is in a sextet?

A

6 peaks, 1:5:10:10:5:1

59
Q

What are homotopic protons?

A

Protons that are equivalent to one another and have the same chemical shift when they are in the same equivalent environment

60
Q

How do you determine equivalency?

A

Look at symmetry and use replacement method

61
Q

What are diastereotopic protons?

A

Protons that are chemically non-equivalent and can and most often do have different chemical shifts

62
Q

What are steps to determining if protons are diastereotopic?

A

Determine a stereo center, draw one diasteromer, replacement method, determine if new stereocenter arises

63
Q

What is the number of peak and relative ratio of doublet of doublet splitting?

A

4 peaks, 1:1:1:1

64
Q

How many peaks and relative intensity is three is a doublet of triplet splitting?

A

2 sets of three peaks with 1:2:1 ratio

65
Q

What is the relative distance of coupling constant in geminal, cis and trans protons?

A

Geminal- small
Cis- medium
Trans- large

66
Q

What are enantiotropic protons?

A

Chemical shift of protons are equivalent and are in equivalent environments. Plane of symmetry

67
Q

If chemical shift is less than 100 what is the hybridization of the C?

A

Sp3

68
Q

If chemical shift is greater than 100, what is the hybridization of the carbon?

A

Sp2

69
Q

In what range would we see a chemical shift peak for C-O?

A

100-50

70
Q

In what range would we see a chemical shift peak for a C=O?

A

Around 200

71
Q

Where is solvent found in carbon NMR?

A

Around 75ppm

72
Q

Where is solvent peak found in proton NMR?

A

Around 7ppm

ochem2 (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions