4.2.3/4.2.4 Organic synthesis and analytical techniques GapFill

During the synthesis of an organic liquid, the reaction mixture is often heated under   refluxredoxreflexredux to prevent the reactants, products and solvent from being boiled away. Once the reaction is complete, the desired product is often separated from other compounds in the mixture through   titrationrecrystallisationcalorimetrydistillation. This technique relies on differences in the compounds'  solubilitiesaciditiesboiling pointsionisation energies.

The product can be analysed in several ways. A common method exploits the absorption of light at different frequencies by different bonds; it is called   visiblemicrowaveinfraredultraviolet spectroscopy, as all the frequencies absorbed lie in this section of the electromagnetic spectrum. (The bonds in atmospheric carbon dioxide, methane and water vapour absorb this type of radiation particularly efficiently, leading to global warming. These molecules are called  heatsinktrappinggreenhouseradiative gases.) The ?-axis of the spectrum shows the frequency of light, measured in   wave crestswave numberswave unitswave figures (cm⁻¹). The ?-axis shows the percentage of the light that is transmitted (i.e. not absorbed). The region of the spectrum below 1500 cm⁻¹ is known as the  indicativeearmarkfingerprintcharacteristic region; it is unique to a given organic molecule, and can be compared to a database of many spectra in order to identify the molecule.

Another analytic tool is mass spectrometry. In the mass spectrum of an organic molecule, the peak with the highest m/z value is caused by the   primaryfundamentalabsolutemolecular ion, which is identical to the original molecule, except that it is missing an electron. (There may be a small peak one m/z unit higher, due to the presence of a carbon-  14131215 atom in the ion.)