Module 4: Chapter 17 (Spectroscopy) Flashcards Preview

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Flashcards in Module 4: Chapter 17 (Spectroscopy) Deck (8)
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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


What are some applications of IR spectrometry?

- used to monitor levels of localised pollution from nitrogen monoxide and hydrocarbons
- IR-based breathalysers measure the ethanol levels in captured breath