17.1 - Mass Spectrometry Flashcards Preview

OCR A Chemistry A Level - Chapter 17 > 17.1 - Mass Spectrometry > Flashcards

Flashcards in 17.1 - Mass Spectrometry Deck (8)
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What is mass spectra used for?

To identify the molar mass of an organic compound and its structure


What is the molecular ion?

- When an organic compound is placed in a mass spectrometer, it loses an electron & forms a +ve ion known as the molecular ion.


What is m/z?

A mass spectrometer detects the m/z (mass:charge ratio) of the molecular ion which gives the molecular mass of the compound.


How do you identify the Mr from a mass spectra?

- M+ peak (molecular ion) must be identified
It is the peak furthest to the RHS of the graph.


What is the M+1 peak?

The M+1 peak is the peak that may appear just after the M+ peak, this is due to the presence of a carbon-13 isotope that increases that compounds Mr by 1. This should not be considered as the Mr of the compound.


What is fragmentation?

- Some molecular ions break down into smaller fragments
- Other peaks are known as fragment ion peaks
- The simplest form of fragmentation breaks down a molecule into a +ve fragment ion and a radical
- The +ve fragment ion will be identified and the uncharged radical won't be detected.


What are common fragment ions?

CH3+: 15
C2H5+: 29
C3H7+: 43
C4H9: 57


What is the formula for working out the number of carbon atoms?

(M+1 peak height)/(M+ peak height) * 100