Brainscape's Knowledge GenomeTM

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


See full index

Mpharm Y2S1 > UV IR Spectroscopy > Flashcards

UV IR Spectroscopy Flashcards

1
Q

Name the electromagnetic spectrum from the largest to the smallest:

A

Radio, Microwaves, Infrared, Visible light, UV, X-rays, Gamma rays

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

Which waves in the EM spectrum are ionising?

A

X rays and Gamma rays

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

What is the wavelength of visible light and what does this diversity represent?

A

750nm- red light= low energy
400nm- blue light= high energy

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

Name and annotate the equation relating energy and wavelength:

A

E= h x c/ wavelength
E= energy (J)
h= Plancks constant
c= speed of light

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

What is the correlation between wavelength and energy?

A

Energy is inversely proportional to wavelength

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

What does ionising radiation mean?

A

Provides enough energy to make or break chemical bonds

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

Give four applications of electromagnetic radiation to spectroscopy:

A
  • Determining the structure of an unknown molecule
  • Confirming the structure of a known molecule (sensitive)
  • Real time monitoring of chemical reactions
  • Trace and impurity analysis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the difference in wavelengths between UV- vis spec and IR spec?

A

UV= 180- 700nm
IR= 2500-25000nm

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

What type of vibration needs to occur in IR spec for it to be visible?

A

Asymmetrical, dipole moment, also bending mode

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

What is a dipole moment?

A

Change in polarity of molecular pair arising in the unequal share of electrons in a bond

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

Why do symmetrical stretch vibrations not show up on IR?

A

They can absorb IR radiation

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

What is wave number? Give the equation:

A

Inverse of wavelength
1/wavelength (cm-1)

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

Give the calculation for wavenumber (Hooke’s Law):

A

V= 4.12 square root of spring constant/ reduced mass

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

What is the correlation between wave number and spring constant?

A

Wave number is proportional to spring constant

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

What is the correlation between bond strength and spring constant?

A

Bond strength is proportional to spring constant

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

What is the correlation between number of bonds and wave number and give an example:

A

Increase in bonds e.g. triple bonds increases wave number as highest IR adsorption
C-C = 1200cm-1
C≡C = 2150cm-1

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

What is the correlation between wave number and reduced mass?

A

Reduced mass is inversely proportional to wavenumber

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

What is the correlation between reduced mass and IR absorption? Give examples:

A

Reduced mass is inversely proportional to IR absorption
C-H = 3000cm-1
C-Cl = 750cm-1
Cl is the heaviest atom in the bond so the lower the IR adsorption wavenumber

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

What do wave numbers above 3000cm-1 represent and give examples:

A

Bonds to hydrogen
N-H = 3300 -3500
O-H = 3200- 3400
C-H = 2850- 3100
C-H (alkyne) 3300
C-H (alkene) 3100

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

What are triple bond wave numbers?

A

2100- 2260 cm-1

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

What is C=O wavenumber?

A

1650- 1800cm-1

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

What do wavenumbers below 1500cm-1 represent and what does this do?

A

Called the fingerprint region
Less useful for finding specific ones but can be diagnostic for a molecule as a whole

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

Describe how the IR wavenumber of a C=O bond can change due to the nature of the group and give examples:

A

-Electron withdrawing groups increase spring constant e.g O (1740cm-1)
-Ketone= (standard 1715)
-Conjugation reduces C=O frequency
-Electron donating groups decrease spring constant e.g N (1655cm-1)

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

What are the three principles for IR spectrometry?

A
  1. Requires a dipole
  2. Gives info about functional groups
  3. Wavenumber is affected by bond strength and atoms in bond
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How does UV irradiation cause DNA damage?

A

Cross-linking of thymine residues

26
Q

What does UV provide in terms of energy?

A

Enough energy for an electron in a molecule to jump to a higher energy orbital

27
Q

Name the energy orbitals in ascending order:

A

Sigma, Pi, Non, Pi star, Sigma star

28
Q

What is the energy jump in carbonyls?

A

n -> π*
sigma -> π*

29
Q

What is the energy jump in halogens and N,O,S?

A

n -> sigma*

30
Q

What is the energy jump in unsaturated compounds?

A

π -> π*

31
Q

What is the energy jump in alkanes?

A

sigma -> sigma*
Largest energy jump

32
Q

Describe a typical UV visible transition:

A

Promotion of an electron from the Highest Occupied Molecular Orbital (HOMO) to the Lowest Occupied Molecular Orbital (LUMO)

33
Q

What are UV executions normally between?

A

HOMOS that contain n or π transitions

34
Q

What is the correlation between conjugation and energy for electronic transition in UV vis?

A

The more conjugation in the π system, the lower energy required for an electronic transition

35
Q

What is a chromophore?

A

A functional group responsible for UV visible absorption

36
Q

What bit of equipment is needed to measure the amount of light transmitted through each wavelength in UV vis?

A

Photodiode

37
Q

State and annotate the equation for the Beer- Lambert law for UV - vis:

A

A= log10 Io/It= ∑cl
A= absorbance
Io= intensity of incidence radiation
It= intensity of transmitted radiation
∑= absorption coefficient
c= conc of sample
l= pathway length

38
Q

What will increasing conjugation do in UV vis spectroscopy?

A

Increase wavelength and absorption coefficient

39
Q

What is an auxochrome and give two examples:

A

Functional group attached to the chromophore which modifies ability of the chromophore to absorb light
e.g lone pair, change in pH

40
Q

Describe and annotate a chromic UV graph:

A

Y axis - absorbance
X axis - wavelength
Hyperchromic (goes up) increase in absorbance
Hypochromic (goes down) decrease in absorbance
Hypsochromic (goes left) shift to shorter wavelength, blue shift
Bathochromic (goes right) shift to longer wavelength, red shift

41
Q

What does lots of conjugation mean in terms of absorbing light?

A

Lots of conjugation will absorb light in the visible region and will be coloured

42
Q

What is florescence?

A

Decay of an excited electron, when EM energy is absorbed it decays by emitting light

43
Q

What is the Quantum yield for a fluorescent process? (ΦF)

A

The ratio of photons emitted through fluorescence to the total number of photons originally absorbed

44
Q

Give the equation for Quantum yield and what is the maximum number?

A

ΦF = photons emitted/ photons absorbed
Max value = 1

45
Q

Give and annotate the equation for the intensity of light emitted after the exciting light is fired off in fluorescence:

A

It= Io exp (-t/ J)
Io= intensity at t= 0
I = intensity at time, t
J (reverse)= mean lifetime of fluorescent state

46
Q

What is green fluorescence protein (GFP)?

A

Naturally produced by jellyfish which is fluorescent
Using recombinant techniques, GFP can be tagged to other proteins
Which can be visualised using fluorescent images

47
Q

How does mass spectrometry work?

A

Molecules are ionised under very low pressure and passed through a magnetic field
The magnetic field will separate the ions according to the mass/charge ratio

48
Q

Name the 3 different mass spectrometry techniques:

A

Electron Impact (EI)
Chemical ionization (CI)
Electrospray Ionization (ESI)

49
Q

Describe electron impact:

A

Sample is vaporized and enters a vacuum chamber where it is bombarded by high energy electrons.
This leads to some molecules losing an electron and forming a positively charged ion M+
Under the energetic conditions, some of these ions will break down into smaller fragments.
The m/z observed will be (M) for the parent molecule and smaller fragments.

50
Q

Describe chemical ionisation:

A

Collisions between ionized solvent and the analyte lead to formation of analyte ions.
Typically, the ions involve addition of a proton (H+). Sometimes, ions can be formed by addition of other cations such as Na+ or K+.
The m/z observed will be (M+cation) e.g.(M+1) for H+ ,(M+23) for Na+,(M+39) for K+ and smaller fragments. The method is less harsh than EI, and less fragmentation is observed.
Reagent gas, NH3, CH4

51
Q

Describe electrospray ionisation:

A

Solution of the sample is passed through very fine capillary at high voltage forming a Taylor cone, leading to a fine spray of droplets. At the Rayleigh limit the droplets break up releasing the ions.
As the solvent evaporates, this produces charged ions that are then analysed by the mass spectrometer. The parent ions are the same as in CI, and there is less fragmentation than EI.

52
Q

What is the base peak in mass spectrometry:

A

Most intense peak

53
Q

What is the molecular ion in mass spectrometry?

A

The highest m/z charge

54
Q

What is the difference between high and low resolution mass spectrometry?

A

Low: gives the m/z value to the nearest whole number
High: gives the m/z value to 4 decimal places or more

55
Q

How many isotopes does chlorine have and give their abundances:

A

Two
Cl35 and Cl37
3:1

56
Q

How many isotopes does bromine have and give their abundances:

A

Two
Br79 and Br81
1:1

57
Q

Is mass spectrometry a spectroscopic method and why?

A

No
No light emitted or recorded in the measurement

58
Q

Name the 5 basic stages of electron impact:

A

Sample input, ionisation, fragmentation, deflection and detection

59
Q

How would you calculate reduced mass?

A

m1m2/m1+m2

60
Q

What does conjugation do to the IR spectrum and why?

A

Decreases the IR value as it weakens the carbonyl bond

Mpharm Y2S1 (12 decks)

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