Analysis and Organic Synthesis Flashcards
What is infrared spectroscopy?
An analytical method used to identify the functional groups in a molecule by measuring the infrared absorption frequencies of its bonds
How does infrared spectroscopy work?
A beam of IR radiation is passed through a sample of a chemical. The covalent bonds absorbs the IR radiation, causing them to vibrate more. Bonds between different atoms absorb different frequencies of IR radiation, so you can tell what bonds are present in the molecule
What is the wavenumber?
Measure used for frequency in IR spectroscopy (it’s just 1 / wavelength)
What does an infrared spectrometer produce after the test?
A spectrum that shows what frequencies of radiation the bonds in the molecule are absorbing
What do the ‘upside down’ peaks on an IR spectra show?
The frequency of radiation that’s been absorbed
Give 2 applications of IR spectroscopy in the real world?
Breathalysers
Monitoring pollutants
How does a breathalyser work?
It measures the amount of ethanol vapour in the driver’s breath by measuring the intensity of the peak for the C-H bond
Why does a breathalyser measure the intensity of the C-H bond rather than an O-H bond or C-O bond?
C-H bonds aren’t affected by any water vapour in the breath
What is a mass spectrum?
A chart produced by a mass spectrometer showing the relative isotopic abundances of an element to work out its relative atomic mass
How does a mass spectrometer work?
The molecules in the sample are bombarded with electrons, so a molecular ion is formed when the bombarding electrons remove an electron from the molecule.
How do you find the relative molecular mass of a compound from a mass spectrum?
Find the molecular ion peak (the peak with the highest mass/charge ratio)
What do the bombarding electrons do to the molecules of the sample, apart from removing an electron to form an ion?
They make some of the molecular ions break up into fragments
What is a fragmentation pattern?
The peaks on a mass spectrum that aren’t the molecular ion peak
How can you differentiate between 2 similar molecules from a mass spectrum?
Every compound produces a different mass spectrum, as they don’t produce exactly the same set of fragments
When given the percentage composition, IR spectrum and mass spectrum, what 4 things do you do to work out the possible structure of the compound?
- Use the composition to work out empirical formula of compound
- Use mass spectrum to work out Mr and use this with empirical formula to find the molecular formula
- Work out functional groups present from IR spectrum
- Use mass spectrum to work out structure of molecule using fragmentation pattern
