UV, Fluoro And IR W7

Question 1

Spectrum

Answer 1

Image

Issac newton 17th century

Describes the dispersion of white light into colours by diffraction

Question 2

Spectroscopy

Answer 2

The study of the interaction between matter and electromagnetic radiation

Question 3

The longer the wavelength the …

Answer 3

Lower the energy the radiation carries

Question 4

Red light

Answer 4

750nm

Lower energy

Question 5

Blue light

Answer 5

400 nm

Higher energy

Question 6

Visible light wavelength

Answer 6

10 to the power of -6 to 10 to the power of -7 m

Question 7

Infrared

Answer 7

10^13 - 10^14 Hz

10^-5 - 10^-6 m

Question 8

UV

Answer 8

10^15 - 10^17 Hz

10^-7 - 10^-9 m

Question 9

When is radiation absorbed by matter

Answer 9

When the energy matches that required for transition between one state and another

Question 10

High frequency =

Answer 10

Short wavelength = high energy = potentially harmful

Question 11

Electromagnetic radiation contains …

Answer 11

Energy which is inversely proportional to the wavelength

Question 12

An example of DNA damage by UV irradiation

Answer 12

Cross-linking of thymine residues

Question 13

Molecular energy levels

Answer 13

Excited electronic state

Ground electric state

Question 14

What does the typical UV visible transition involve?

Answer 14

Promotion of an electron from the highest occupied molecular orbital HOMO to the lowest occupied molecular orbital LUMO

Question 15

Strongest bond in a molecule

Answer 15

Sigma bond

Question 16

Where are UV excitations usually?

Answer 16

Between HOMOs that contain N or P electrons

Question 17

The more conjugated the P system…

Answer 17

The lower the energy required for an electronic transition

Question 18

Chromophore

Answer 18

The functional group responsible for UV visible absorption

Increasing conjugation will increase y and E
Cis double bonds give longer y but lower E
Can be affected by solvents and pH

y = wavelength
E = absorbtion coefficient

Question 19

Beer lambert law

Answer 19

A = log10 (i0/it) = ECL

A= Absorbance
i0 = Intensity of incident radiation
it = Intensity of transmitted
radiation ε = absorption
coefficient c = concentration of
sample l = path length

Question 20

Auxochrome

Answer 20

functional group attached to the chromophore which modifies the ability of the chromophore to absorb light
– eg lone pair
– Can change with pH eg if deprotonation increases conjugation

Question 21

Bathochromic

Answer 21

shift to longer wavelength (red shift)

Question 22

“Hypsochromic

Answer 22

shift to shorter wavelength (blue shift)

Question 23

Hypochroism

Answer 23

“Hypochroism

Question 24

Hyperchroism

Answer 24

increase in
absorbance

Question 25

Aromatics

Answer 25

Simple aromatic compounds absorb light in the UV region, and will be
colourless.

Question 26

Alkenes

Answer 26

simple alkenes absorb in the UV end of the spectrum.

They will be colourless.

highly conjugated natural products absorb light in the visible region, and will be coloured as a result. Ie carrot and tomato

Question 27

UV-visible Absorption in Biomolecules

Answer 27

• Proteins absorb at 280 nm due to the amino acids tryptophan and tyrosine.
• Coloured proteins exist e.g. haemoglobin due to complexation with iron containing heme.
• Nucleic acids absorb at 260 nm due to the nitrogen heterocycles.
• Many natural products are coloured, absorbing in the visible region.

Question 28

Monitoring reactions

Answer 28

Design of coloured dyes by modulation of the chromophore

• HPLC usually uses a UV trace
– eg monitor at 254 nm

• TLC can use UV to visualise

Question 29

Fluorescence: decay of the excited electron

Answer 29

Sometimes when EM energy is absorbed it decays by emitting light.

This can be by the slow process of phosphorescence or by the rapid process of fluorescence.

Ff = photons emitted / photons absorbed

Max value of Ff is 1

Question 30

Green Fluorescent Protein

Answer 30

• GFP naturally produced by jellyfish is fluorescent due to a spontaneous chemical reaction within its protein structure.
• GFP can be tagged to other proteins.
• This allows the tagged protein to be visualised by fluorescent imaging.

Question 31

Fluorescence Based High-throughput Screening

Answer 31

• The rate of enzyme reaction is measured by a probe that reacts with the cofactor NADH to produce red fluorescence.

• If the sample contains an inhibitor of the enzyme, less NADH will be consumed leading to increased fluorescence

• Fluorescence can be detected at lower levels than UV-visible absorption,

Question 32

Kcal to kj

Answer 32

X 4.18

Question 33

Vibrational Transitions : equilibrium

Answer 33

No vibrations
No dipole change
No IR absorption

Question 34

Vibrational Transitions : symmetric stretch

Answer 34

Vibration side to side
No dipole change
No IR absorption

Question 35

Vibrational Transitions : bending mode

Answer 35

Movement up and down
Dipole change
IR absorption

Question 36

Asymmetric stretch

Answer 36

One side stretching more than the other
Change in dipole
IR absorption

Question 37

Infrared Spectroscopy and Functional Groups

Answer 37

By measuring the IR abrorptio of a molecule we can identify the FGs

Each bond have different frequency for a vibrational transition

Question 38

Wave number

Answer 38

Inverse of wave length

1/y = n

Question 39

The stronger the Bon …

Answer 39

The higher the IR absorption wave number

C=C higher than C-C

Question 40

Wave number is proportional to…..

Answer 40

Spring constant which is proportional to bond strength

Question 41

Reduced mass is inversely proportional to…

Answer 41

IR absorb frequency

C-H = 3000cm-1

C-Cl = 750cm-1

Question 42

Heavier the atoms in the bond the…

Answer 42

Lower the frequency

Question 43

Characteristic IR Frequencies

Answer 43

N-H stretch / O-H = >3000
C-H stretch = 3000
N-CH3 = 2800
CtripleN = 2100
CtripleC = 2100
C=O stretch stretch = 1700
Fingerprint = <1500

Question 44

What affects C=O frequency

Answer 44

E.withdrawing group increases K ad increases wave no.

Conjugation reduce C=O frequency, decrease bond strength and decrease wave no.

E.donating group decreases spring constant and decreases wave number