Arene substitution pattern
Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon. Ortho, meta, and para substitution In ortho-substitution, two substituents occupy positions next to each other, which may be numbered 1 and 2. In the diagram, these positions are marked R and ortho. In meta-substitution the substituents occupy positions 1 and 3 (corresponding to R and meta in the diagram). In para-substitution, the substituents occupy the opposite ends (positions 1 and 4, corresponding to R and para in the diagram). The toluidines serve as an example for these three types of substitution. Synthesis Electron donating groups, for example amino, hydroxyl, alkyl, and phenyl groups tend to be ortho/para-directors, and electron withdrawing groups such as nitro, nitrile, and ketone groups, tend to be meta-directors. Properties Although the specifics vary depending on the compound, in simple disubstituted arenes, the three isomers tend to have rather similar boiling points. However, the para isomer usually has the highest melting point, and the lowest solubility in a given solvent, of the three isomers. Separation of ortho and para isomers Because electron donating groups are both ortho and para