Analytical Techniques 4.2.4

Question 1

What are the two types of vibration?

Answer 1

Stretching

Bending

Question 2

How can we use infrared radiation to find out which bonds are present in a molecule?

Answer 2

Each chemical covalent bond absorbs a different wavelength of infrared radiation, when IR passes through a molecule, the wavelengths absorbed tells us which bonds are present in that molecule.

Question 3

On the infrared spectroscopy graph what are the units of measurement for transmittance and frequency?

Answer 3

% transmittance

Frequencies are measured in cm-1

Question 4

Where is the fingerprint region?

Answer 4

To the right of 1500 - 500

Question 5

Why are OH peaks broad?

Answer 5

They are broad due to hydrogen bonding between molecules

Question 6

What does a peak at 3300 indicate is present?

Answer 6

O-H bond

Question 7

What can we use the fingerprint region and why is it special?

Answer 7

No two compounds have the same fingerprint, this bit can be used to confirm the exact identity of a compound just like human fingerprints.

Question 8

Where is fingerprinting used in the medical industry?

Answer 8

When a new drug is formed it can be patented

Question 9

How can we identify an aldehyde or a keystone?

Answer 9

There is a C=O at about 1700 but there is no OH.

There may be a small OH stump but it is not a significant peak

Question 10

If there is a ketone or an aldehyde present why might there be a small stump where the OH group normally is?

Answer 10

Water may still be in the sample

Question 11

What do we see when a Carboxylic acid is present?

Answer 11

A very broad OH that blends into the CH stretching

Question 12

Name 3 uses for Infrared Spectroscopy

Answer 12

• Monitor air pollution by measuring the concentration/ abundance of atmospheric pollutants (CO & NO)
• Drug detection
• Quality a control in perfume production
• Monitoring the degree of unsaturation in polymers
• Breathalysers

Question 13

What are the environmental issues concerning IR radiation?

Answer 13

Greenhouse gases have bonds and their bonds absorb IR whilst they are in the atmosphere and that is why we have this problem

Question 14

List two ways in which greenhouse emissions can be reduced

Answer 14

• Burn less fossil fuels/use renewable energy sources
• Hybrid cars, make them more efficient
• Biofuels
• Reduce deforestation

Question 15

What happens in mass spectrometer, what does the graph show?

Answer 15

In the mass spectrometer an organic molecule loses an electron to form the molecular ion

Question 16

What is a radical?

Answer 16

A species with an unpaired electron

Question 17

How can we find out the Mr from the mass spectrometry graph?

Answer 17

The molecular ion peak/M+ peak, it’s the peak which is the furthest to the right

Question 18

Write a fragment for ethanol

Answer 18

[CH3CH2OH]+
[CH2OH]+
[CH3CH2]+
[CH3]+

Question 19

What must you remember to put for all molecular ions/fragment ions

Answer 19

+ve charge

Question 20

All organic molecules absorb infrared radiation what does this absorbed energy do to the bonds?

Answer 20

It makes bonds in the molecules vibrate more strongly