Flashcards in Module 4: Chapter 17 (Spectroscopy) Deck (8)
What can mass spectrometry do?
1. identify the molecular mass of an organic compound
2. give further information about the structure
How is the molecular mass determined in mass spectrometry?
- in the spectrometer the molecule loses an electron to form a positive ion (ion is called the molecular ion)
- m/z ratio detected of the ion and it shows up as the highest mass peak on the spectrum (the molecular ion peak)
- assuming z = 1 its value will be equivalent to the molecular mass of the compound
What is fragmentation?
- some molecular ions break down into smaller fragments
- two species are formed; a positively charged fragment ion and an uncharged radical
- peak heights reflect the likely hood of the particular fragmentation (the positively charged fragment, no the lost species)
What are some applications of mass spectrometry?
- all molecule fragment in slightly different ways according to their structure, therefore a compound's mass spectrum is unique and can be used to identify it (unknown compounds)
- mass spectrometry is amongst the techniques used in sport to test urine samples for banned substances
What happens to covalent bonded molecules with IR?
- covalent bonds in molecule posses energy and have a natural vibration about a central point
- they can absorb infrared radiation, this makes them vibrate more
- vibrates can be stretches or bends (bends change bond angle)
- only absorbs IR that has the same frequency as the natural frequency of the bond
What does the amount that a bond stretches or bends depend on?
1. the mass of atoms (heavier = slower vibration)
2. the strength of bonds (stronger = faster vibration)
wavenumber = ...
1 / wavelength in cm^3
- wavenumber is directly proportional to frequency