C Unit 2.8 Instrumental Analysis

Question 1

Advantage of instrumental anaylsis?

Answer 1

• Require very small samples:
  less damaging or invasive
  Important if there is very little of the original to identify
• They are quick to carry out
• They give very accurate data

Question 2

What are the 3 spectrometry’s you’ll be looking at?

Answer 2

1. Mass spectrometry
2. Infrared spectrometry (IR)
3. Nuclear Magnetic Resonance spectroscopy (NMR)

Question 3

What’s a mass spectrometer?
(3 things)

Answer 3

• An analytical technique
• Used to identify different isotopes
• And find overall relative atomic mass of an element

Question 4

Explain step 1: Ionisation in mass spectrometry?
(5 things)

Answer 4

1. A sample of an element is vapourised and injected
   - Into mass spectrometer
   - Where high voltage passed over chamber
   - Causes electrons to be removed from atoms (ionised)
   - Leaving 1+ charged ions in chamber

Question 5

Explain step 2: Acceleration in mass spectrometry?
(2 things)

Answer 5

2. Positively charged ions are accelerated towards
   - Negatively charged detection plate

Question 6

Explain step 3: Ion drift in mass spectrometry?
(4 things)

Answer 6

3. Ions deflected by magnetic field
   - Into a curved path
   - Radius of their path dependent on
   - Charge & mass of ion

Question 7

Explain step 4: Detection in mass spectrometry?
(4 things)

Answer 7

4. When positive ions hit negatively charged detection plate,
   - They gain an electron
   - Producing flow of charge
   - Greater current produced = greater abundance

Question 8

Explain step 5: Analysis in mass spectrometry?
(4 things)

Answer 8

5. Current values used in combination
   - With flight times to produce
   - Spectra print-out
   - With relative abundance of each isotope displayed

Question 9

In mass spectrum, why do we see a half traced version of the ion?
(5 things)

Answer 9

• During ionisation process, 2+ charged ion may be produced
• Will be affected more by magnetic field
• Producing curved path of a smaller radius
• As a result, mass to charge ratio (m/z) is halved
• Can be seen on spectra as a trace at half the expected m/z value

Question 10

In mass spectrum:
What m/z?
What relative abundance?

> _>

Answer 10

1. Mass to charge ratio
2. Relative atomic mass?

icl i haven’t seen where u had to put a number for a certain bar so i reckon u don’t get fucked up by this one

I changed it lol

Question 11

For mass spectra graph, how u gain mass for the 2 isotopes

Answer 11

Formula for mass of 2 isotopes:

1(relative abundance x m/z)+2(relative abundance x m/z)/ra1 + ra2

May seem a lil hard to remember but gl bro B)
^ past me said that

Question 12

Define molecular ion (M₊)

Answer 12

The positive ion formed in a mass spectrometer from the whole molecule

Question 13

Define fragementation

Answer 13

Splitting of molecules in a mass spectrometer into smaller parts

Question 14

How to identify molecular ions in a mass spectrum?
(4 steps)
(Major check-up)

Answer 14

Don’t take my word for it, for now
1. Assume there’s a fragment table?
2. U look at m/z (x-axis)
3. Check which bars correlate to what’s in the fragment table
4. Then it’s all about deduction based on what’s also not there

Question 15

Describe infrared spectroscopy
(3 things)

Answer 15

• Infrared radiation absorbed by organic molecules
• Causes increased bending and vibrations

Question 16

For Infrared spectroscopy, what does “different bonds absorb different energies” mean?
(3 things)

Answer 16

• Said to be the characteristic of the bonds
• The absorptions on the spectra can indicate
• which groups of atoms are present

Question 17

What is energy absorbed in IR spectroscopy measured in?

Answer 17

wavenumbers (units cm^-1)

Question 18

Which parts of a molecule absorb infrared energy?

Answer 18

The bonds

Question 19

Define wave number

Answer 19

A measure of energy absorbed used in IR spectra

Question 20

Define characteristic absorption

Answer 20

The wavenumber range at which a particular bond absorbs radiation

Question 21

How to identify chemical compounds in a IR spectrum?
(4 things)

Answer 21

• U must use the data booklet for the wavenumber as it will guide u to identify bonds within the IR spectrum
• Not based on peaks but based on troughs (the opposite of peaks)
• Be aware of the wave number (must be within range)
  -. After gaining the bonds, gain mr and use ur brain to create the structural formula or molecular formula

Question 22

What typical troughs u should know for IR spectrum?
(2 things)

Answer 22

C=O bond - deep trough at 1700
O-H bond - usually within broad trough around 3000

Question 23

An example of an IR spectroscopy?

Answer 23

Breathalysers

Question 24

Issue with breathalysers against drunk ppl and ketosis?

Answer 24

Both have functional group carbonyl bond
However can spot the one who drank too much alcohol:
O-H = carboxylic acid = 2500 - 3550

Question 25

Describe Nuclear Magnetic Resonance (NMR) Spectroscopy
(5 things)

Answer 25

• Corresponds to the energy required
• to reverse the spin of the nucleus
• of an atom within a magnetic field.
• Causes resonance
• Energy absorbed is shown by chemical shift, δ

Must know how to interpret the spectra of this

Question 26

An example of an NMR spectroscopy?

Answer 26

MRI scanner ig

Question 27

How to identify compounds in an NMR spectra?
(might need more work)
(5 steps)

Answer 27

• It’s based on environments with n° of “protons”
• U have data booklet for the chemical shifts
• Number of peaks based on number of environments
• Where they placed based on chemical shift
• Height of peak (frequency) based on number of hydrogens (n° of protons)

Question 28

Propan-1-ol
How would u describe the environments of each of the hydrogens?

Answer 28

• 4 environments
• and so “8 protons”
• Create graph:
  1. 4 bars based on n° of environments
  2. Height based on n° of protons of each environment
  3. But how do i figure out where it’s placed….

Question 29

Describe ¹³C (NMR) Spectroscopy

Answer 29

Based on the carbon atoms and it’s bonds

Question 30

If too unsure, still possible to go back

Answer 30

I need to do questions tho

Question 31

LET’S GO GAMBLING

Answer 31

99% of Gamblers…