17.2 Infrared spectroscopy Flashcards
What happens to bonds when they absorb Infrared radiation?
The bonds can bend or stretch more
What types of vibrations are there?
A stretch
A bend
What happens during a stretch?
A rhythmic movement along the line between the atoms
so distance between the atom increases and decreases
What happens in a bend?
Bond angles change
What affects a bond stretch or bend amount?
The mass of the atoms in the bond
Heavier = slower
Strength of bond
Strong bonds = faster
Why do organic chemists use infrared spectroscopy?
To identify functional groups present in the organic molecules
Describe the steps of infrared spectroscopy
- Sample is placed inside IR spectrometer
- Beam of IR radiation in range 200-4000cm-1 is passed through sample
- The molecule absorbs some IR radiation and a beam is used to detect frequency absorbed
- IR spectrometer usually connected to a computer that plots a graph of transmittance against wavenumber
What is the fingerprint region?
A region with unique peaks that can be used the particular molecule under investigation
What does the round bottomed curve indicate?
O-H in alcohols
What does a sharp peak indicate?
C=O from aldehyde or ketone
What does a gradual increase peak followed by a sharp peak indicate?
O-H in carboxylic acid
C=O (sharp peak)
How can pollutants be identified?
By their IR spectral fingerprints
How can police use IR spectrometry?
In breathalysers
Beam of IR radiation passes through the captured breath in sample chamber and detect IR absorbance of compound
What do breathalysers measure?
Amount of ethanol
What is elemental analysis?
Use of percentage composition data to determine empirical formula
