Organic Analysis
16.1 Test-tube Reactions 16.1 Test-tube reactions
Test for alkenes:
16.2 mass spectrometry
- Shake with bromine water
- Orange to colourless 16.3 infrared spectroscopy
Test for halogenoalkanes:
- Add NaOH(aq) and warm, acidify with HNO3 and add AgNO3(aq)
- AgX precipitate forms (X is the halide)
Test for alcohols:
- Add potassium dichromate
- Orange to green for primary and secondary alcohols
Test for aldehydes:
- Warm with Fehling’s or Tollens solution
- Blue to brick red precipitate or silver mirror forms
Test for carboxylic acids:
- Add NaHCO3(aq)
- CO2 given off
16.2 Mass Spectrometry
- High resolution mass spectrometers allow us to work out the molecular formula.
- An ion with a mass of 200 to the nearest whole number could have the molecular formulae of:
C10H16O4, C11H4O4 or C11H20O3. However, using the accurate atomic masses allow us to distinguish
between them.
C10H16O4 = 200.1049
C11H4O4 = 200.0110
C11H20O3 = 200.1413
16.3 Infrared Spectroscopy
- Infrared spectroscopy is used to identify bond in a molecule, at
a specific frequency a bond will absorb energy from infrared
waves and move to a higher vibrational level. This is called the
resonance frequency and depends on the type of bond.
- The amount a bond stretches, or bends depends on the mass
of the atoms in the bond (heavier atoms vibrate slower)and the
strength of the bond (stronger bonds vibrate faster).
- Infrared spectrometry works by:
o A beam of infrared radiation is passed through a sample
o The radiation that comes through the other side is missing the frequencies that are found in
the bonds in the sample.
o A graph is plotted of the intensity of the radiation against the frequency of radiation. The
frequency is expressed as a wavenumber measured in cm-1.
!
Wavenumber = "#$%&'()%* (-()
- Above 1500cm-1 is used to identify functional groups, below 1500cm-1 O – H alcohols 3200-3600
is used for fingerprinting. O – H carboxylic acids 2500-3200
- Peaks show frequencies of infrared radiation that are absorbed by C=O 1630-1740
bonds. C–H 2850-3100
- The fingerprint region is unique for every compound.
16.1 Test-tube Reactions 16.1 Test-tube reactions
Test for alkenes:
16.2 mass spectrometry
- Shake with bromine water
- Orange to colourless 16.3 infrared spectroscopy
Test for halogenoalkanes:
- Add NaOH(aq) and warm, acidify with HNO3 and add AgNO3(aq)
- AgX precipitate forms (X is the halide)
Test for alcohols:
- Add potassium dichromate
- Orange to green for primary and secondary alcohols
Test for aldehydes:
- Warm with Fehling’s or Tollens solution
- Blue to brick red precipitate or silver mirror forms
Test for carboxylic acids:
- Add NaHCO3(aq)
- CO2 given off
16.2 Mass Spectrometry
- High resolution mass spectrometers allow us to work out the molecular formula.
- An ion with a mass of 200 to the nearest whole number could have the molecular formulae of:
C10H16O4, C11H4O4 or C11H20O3. However, using the accurate atomic masses allow us to distinguish
between them.
C10H16O4 = 200.1049
C11H4O4 = 200.0110
C11H20O3 = 200.1413
16.3 Infrared Spectroscopy
- Infrared spectroscopy is used to identify bond in a molecule, at
a specific frequency a bond will absorb energy from infrared
waves and move to a higher vibrational level. This is called the
resonance frequency and depends on the type of bond.
- The amount a bond stretches, or bends depends on the mass
of the atoms in the bond (heavier atoms vibrate slower)and the
strength of the bond (stronger bonds vibrate faster).
- Infrared spectrometry works by:
o A beam of infrared radiation is passed through a sample
o The radiation that comes through the other side is missing the frequencies that are found in
the bonds in the sample.
o A graph is plotted of the intensity of the radiation against the frequency of radiation. The
frequency is expressed as a wavenumber measured in cm-1.
!
Wavenumber = "#$%&'()%* (-()
- Above 1500cm-1 is used to identify functional groups, below 1500cm-1 O – H alcohols 3200-3600
is used for fingerprinting. O – H carboxylic acids 2500-3200
- Peaks show frequencies of infrared radiation that are absorbed by C=O 1630-1740
bonds. C–H 2850-3100
- The fingerprint region is unique for every compound.
