6.2.4/6.2.5/6.3 Carbon–carbon bond formation, organic synthesis and analysis GapFill

Nuclear magnetic resonance (NMR) involves placing a sample in   a magnetica focalan electrica birefringent field, then bombarding it with electromagnetic waves from the  radioX-raygamma raymicrowave region. The resulting spectra have a quantity called chemical shift on their x-axes. Chemical shift has units of  parts per billion (ppb)parts per million (ppm)parts per quadrillion (ppq)parts per trillion (ppt), and is represented by the symbol  σβδγ. The chemical shift of a nucleus is related to the electron density surrounding it: the higher the electron density, the lower the chemical shift. Nuclei with a high electron density around them are said to be  shieldedinsulatedguardedprotected.

¹H (proton) spectra offer more information than ¹³C spectra. Firstly, protons show spin-spin  couplingrelationunitypairing, causing signals to split according to the  n+1n-12n-12n+1 rule. This gives information on the number of protons attached to adjacent carbon atoms. Furthermore,  cipheredlinearisedintegrateddifferentiated ¹H spectra display the relative area under each signal, which corresponds to the relative number of protons in each environment.

Chromatography allows chemists to separate and, in some cases, identify the components of a mixture. There are several types of chromatography, but all of them rely on the use of both a stationary phase and   an acceleranta mobilea liquida processive phase (sometimes referred to as the  fluentinfluenteluenteffluent in column chromatography). In general, separation occurs because each component in the mixture has a characteristic balance of solubility in the solvent and  antipathyaminityaffinityamenity for the stationary phase, which is determined by molecular properties such as polarity. Gas chromatography (GC) is slightly different in that the solvent is replaced by an inert carrier gas, which pushes the vaporised mixture through a tube packed with the stationary phase. A gas chromatogram displays a  retentionlenitionreactiondetention time for each component, which can be identified by comparing this value with those in a library of reference compounds. (A similar process, instead using   RSRFSQRT values, allows compounds to be identified by thin-layer chromatography.)