Asked by Andy Blackwell Uncategorized
What are sterioisomerism?
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Asked in Chemistry
What is isomerism in organic chemistry?
When all types of isomers are taken in general, they can be defined as the compounds with the same molecular formula but with different chemical and/or physical properties. There are three main types of isomers; namely constitutional isomers, stereoisomers and conformational isomers. Constitutional isomers have different bonding structures, hence they exhibit different chemical properties. Some examples are; butane -- 1-methylpropane pentane -- 2-methylbutane -- 2,2-dimethylpropane and so on... Let us now consider about stereoisomers, they have similar bonding structures, but the three dimensional arrangement is different. They show only altered particular physical properties. Consider the compound CHClFBr.Draw one of possible structures with the central carbon atom, and the other bonds as desired. Now swap any two bonds and draw the new structure. Now imagine about the superimposition of these two molecules in three dimensional space. It is impossible (most likely the fact that we cannot superimpose our hands). Such carbon atoms in these compounds are known as 'chiral' and more formally as 'steriogenic'. The cis-trans isomerism also belongs to the sterioisomerism. However, the necessity to show sterioisomerism in olefenic compounds is to have at least one pair of identical bonds in the two carbon atoms with double bonds. These compounds can be recognized ONLY with polarized light. The compounds which turn light clockwise is known as d-compounds and for the anticlockwise is known as l-compounds, (which are derived from the Latin words dextro and lacto). Finally, we'll have a look at conformational isomers. As we know, atoms beside a bond can rotate as taking the bond line as its axis. Hence the bonds angles would be differed every moment in most of organic compounds. Although there are infinite conformational isomers to a given compound, it is often practical to draw the most stable ones chosen from them. If cyclohexane is considered as an example, the two different 'chair conformations' and the intermediate 'boat confirmation' are well recognized.