IR Spectroscopy And Chromatography Flashcards
3 things that mass spectroscopy can identify
Relative isotopic mass
Abundance of different isotopes
Relative molecular mass
What does IR spectroscopy consist of
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
IR spectroscopy can also be used to find out
How pure a compound is and identify any impurities. Impurities produce extra peaks in the fingerprint region
IR spectroscopy can identify….
Organic molecules
What are molecular ions
Formed when molecules have electrons knocked off
The Molecular ion can be broken into…
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
When breaking molecular ions into fragments, the more stable fragments give…
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
2 examples of stable fragment ions
Carbocations and acylium ions
Why do carbocations form stable fragment ions
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
Why do acylium ions form stable fragment ions
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
If a molecule has resonance forms, it….
Changes between them very quickly
What does NMR stand for
Nuclear magnetic resonance
13C NMR info
Gives you info on how the carbon atoms in a molecule are arranged and the number of carbon environments within the molecule
1H NMR info
Tells you how the hydrogen atoms in a molecule are arranged
2 types of NMR
13C NMR
1H NMR
Nuclei in different environments absorb…… Explain
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
Chemical shift is measured relative to…
Tetramethylsilane (inert)
Give 2 reasons why TMS is used as a standard in recording NMR spectra
All the hydrogens and carbons are in the same environment
Low boiling point/ volatile
What is chromatography used for
The separates substances in a mixture. Once they have been separated, you can identify the components
What are the 2 types of chromatography
Column and gas-liquid
All types of chromatography have 2 phases. These are…
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
