IR Spectroscopy And Chromatography

Question 0

3 things that mass spectroscopy can identify

Answer 0

Relative isotopic mass
Abundance of different isotopes
Relative molecular mass

Question 1

What does IR spectroscopy consist of

Answer 1

Beam of IR radiation passes through sample

IR energy absorbed by bonds in molecules, increasing vibrational energy

Different bonds absorb different wavelengths. Bonds in different environments in a molecule absorb different wavelengths

Question 2

IR spectroscopy can also be used to find out

Answer 2

How pure a compound is and identify any impurities. Impurities produce extra peaks in the fingerprint region

Question 3

IR spectroscopy can identify….

Answer 3

Organic molecules

Question 4

What are molecular ions

Answer 4

Formed when molecules have electrons knocked off

Question 5

The Molecular ion can be broken into…

Answer 5

Smaller fragments by the larger number of electrons. The fragments that are ions show up on the mass spectrum, making a fragmentation pattern. Fragmentation patterns can be used to identify molecules and even their structures

Question 6

When breaking molecular ions into fragments, the more stable fragments give…

Answer 6

Higher peaks.

Some fragment ions are more stable than others, so more likely to form. That means they will be more abundant so will have higher peaks on mass spectrum

Question 7

2 examples of stable fragment ions

Answer 7

Carbocations and acylium ions

Question 8

Why do carbocations form stable fragment ions

Answer 8

A carbocation is an ion with a positively charged carbon. They are relatively stable ions because alkyl groups feed electrons towards the positive charge. Carbocations with more alkyl groups are more stable

Question 9

Why do acylium ions form stable fragment ions

Answer 9

The acylium ion is often formed from aliphatic ketones. Has resonance forms, resonating between 2 or more different structures helps stabilise what would otherwise be an unstable ion

Question 10

If a molecule has resonance forms, it….

Answer 10

Changes between them very quickly

Question 11

What does NMR stand for

Answer 11

Nuclear magnetic resonance

Question 12

13C NMR info

Answer 12

Gives you info on how the carbon atoms in a molecule are arranged and the number of carbon environments within the molecule

Question 13

1H NMR info

Answer 13

Tells you how the hydrogen atoms in a molecule are arranged

Question 14

2 types of NMR

Answer 14

13C NMR

1H NMR

Question 15

Nuclei in different environments absorb…… Explain

Answer 15

Different amounts of energy

A nucleus is partly shielded from the effects of an external magnetic field by its surrounding electrons. Any other atoms and group of atoms that are around a nucleus will also affect the amount of electron sheilding. So the nuclei in a molecule feel different magnetic fields depending on their environments. Means they absorb different amounts of energy at different frequencies

Question 16

Chemical shift is measured relative to…

Answer 16

Tetramethylsilane (inert)

Question 17

Give 2 reasons why TMS is used as a standard in recording NMR spectra

Answer 17

All the hydrogens and carbons are in the same environment

Low boiling point/ volatile

Question 18

What is chromatography used for

Answer 18

The separates substances in a mixture. Once they have been separated, you can identify the components

Question 19

What are the 2 types of chromatography

Answer 19

Column and gas-liquid

Question 20

All types of chromatography have 2 phases. These are…

Answer 20

A mobile phase- where the molecules can move. This is always a liquid or gas

A stationary phase- where the molecules can’t move. This must be a solid, or a liquid held in a solid