Organic analysis 16 Flashcards
test for alkene
shake with bromine water
orange colour disappears
test for halogenalkane
1 add NaOH(aq) and warm
2 acidify with HNO3
3 add AgNO3(aq)
the precipitate of AgX
test for alcohol
add acidified K2Cr2O7
orange colour turns green with primary and secondary alcohols
test for aldehydes
warm with Fehling’s solution / Tollen’s solution
blue colour turns red / silver mirror
test for carboxylic acid
add NaHCO3(aq)
CO2 given off
fragmentation (molecular ion)
many ions will then break up because some of their bond breaks as they are ionised.
each of the fragment creates a line
High-resolution mass spectrometry
can measure masses to three or four decimal places you can work out the molecular formula of the parent ion
infrared spectroscopy works
- a pair of atoms joined by a chemical bond is always vibrating. (like two balls and a spring)
- stronger bonds vibrate faster and heavier atoms vibrate slower.
- every bond has its own unique natural frequency that is in the infrared region of the electromagnetic spectrum
- when you shine a beam of infrared radiation through the sample, the bonds in the sample can absorb energy from the radiation and vibrate more but can only absorb the energy of the same frequency. radiation that emerges from the sample will be missing the frequencies
infrared spectrometer
1 a beam of infrared radiation containing a spread of frequencies is passed through a sample
2 radiation that emerges is missing the frequencies that correspond to the types of bonds found in the sample
3 instrument plots a graph of the intensity of the radiation emerging from the sample against the frequency of radiation
4 frequency expressed as a wavenumber
fingerprint region
-area of an infrared specctrum below 1500cm-1
the shape is unique for any particular substance, it can be –idenify the chemical.
-a chemist can use a computer to match fingerprint region of a sample with those on a database of compounds.
mass spectrometry
relative atomic mass
ionised, so postive Iona are accelerated through the instrument towards detector
flights of time measure (mass to charge ratio)
used in drug testing
(Mass spectrometry can be used to determine the molecular formula of a compound)
GCM’s
gas chromatography mass spectrometry
used in forensic work
separating mixtures of vapours through a tube packed with a powdered solid
oxidation state
number of electrons lost or gained by an atom in a compound compared to the uncombined atom
what happens in a infrared spectrometer
(Bonds in a molecule absorb infrared radiation at characteristic wavenumbers.
‘Fingerprinting’ allows identi cation of a molecule by comparison of spectra.)