B4 Organic analysis
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what is mass spectra used to identify?
the molecular mass of an organic compound gain further information about its structure - fragment ions
what does the furthest peak on the mass spectrum indicate?
M+ peak - indicates the molecular mass of the molecular ion
what is the M+1 peak?
very small peak one unit after the M+ peak - exists because 1.1% of carbon is present as the carbon-13 isotope
Common fragment ions: CH3+
m/z = 15
Common fragment ions: C2H5+
m/z = 29
Common fragment ions: C3H7
m/z = 43
Common fragment ions: C4H9+
m/z = 57
What does infrared radiation cause?
causes covalent bonds to vibrate (bend/stretch) more and absorb energy
Define the term elemental analysis
use of percentage composition data to determine the empirical formula
Define the term mass spectrometry
use of the molecular ion peak from a mass spectrum to determine the molecular mass - use of fragment ions to identify sections of a molecule
Define the term infrared spectroscopy
use of absorption peaks from an infrared spectrum to identify bonds and functional groups present in the molecule
Describe how infrared spectroscopy works.
bonds absorb IR radiation, causing vibrations vibrations at particular frequencies produces a spectrum of different absorptions corresponding to the different bonds
Each IR spectrum has a peak around 3000cm-1. Explain why there is such a peak.
All of the compound have alkyl groups (C–H bonds) which absorb at similar frequencies
Explain how infrared spectroscopy could be used to confirm that cyclohexene had been reacted to form cyclohexane.
Peak at 1620-1680 cm-1 will disappear on formation of cyclohexane
Explain why infrared radiation is linked to climate change.
Gases associated with climate change (e.g. CO2) have bonds which absorb infrared radiation and trap it inside the Earth’s atmosphere
What is one way governments have responded to the evidence that IR radiation is linked to climate change?
switching to renewable energy supplies
What are the uses for infrared spectroscopy other than identifying the functional groups in unknown compounds in the lab?
Monitoring of atmospheric pollution Breathalyser tests