Organic Analysis Flashcards
Test for alkene
Shake with bromine water and the solution goes from orange to colourless.
Test for haloalkanes
Add warm aqueous NaOH. Acidity with nitric acid. Add silver nitrate and a precipitate of a silver halide will form.
Test for primary or secondary alcohol
Add acidified potassium dichromate. Orange colour turns green.
Test for aldehydes
Warm with Tollens’ reagent and a silver mirror forms.
Test for carboxylic acids
Add sodium hydrogencarbonate and CO2 is given off (effervescence).
Why can high resolution mass spectrometry better at distinguishing between molecules than normal mass spectra?
Because it can give the molecular mass to four decimal places which makes use of the fact that atoms don’t have an exact whole number atomic mass (apart form C-12 by definition). Normal mass spectra only give the mass of the molecule to the nearest whole number which could have multiple possible molecular formulae.
How does infrared spectroscopy work?
A pair of atoms joined by a chemical bond is always vibrating. Stronger bonds bonds vibrate faster (higher frequency) and heavier atoms make the bonds vibrate slower (lower frequency). Every bond has a unique natural frequency that is in the IR region of the EM spectrum. When IR is shone through a sample, the bonds can only absorb the energy from the radiation with exactly the same frequency as its natural frequency. Therefore the radiation emerging from the sample will be missing the frequencies that correspond to the bonds in the sample.
What happens in an infrared spectrometer?
A beam of IR of a spread of frequencies is passed through a sample. The emerging radiation is missing the frequencies that correspond to the types of bonds in the sample. The instrument plots a graph of the intensity of radiation (transmittance) against its frequency which is expressed as a wavenumber (cm^-1).
Types of peak on an infrared spectrum
O-H (alcohol) is large smooth curve
O-H (carboxylic acid) is large jagged curve
C=O is deep thin peak
C-O is similarly deep thin peak.
What is the fingerprint region of an infrared spectrum?
That area of the spectrum below 1500cm^-1. It usually has many peaks and is unique for any particular substance.
What is wavenumber?
1/wavelength
Measured in cm^-1
