In organic chemistry, there is this concept of aromaticity that is very important in determining the stability of a compound. In order to determine if a compound is aromatic, anti-aromatic, or non-aromatic (there is a difference between anti- and non-), the number of pi electrons must be determined. This can be done very simply using 3 simple rules that follow a hierarchy system. This essentially means that out of the three rules, if one rule applies compared to the other, one of the rules will override the other due to it having a higher priority. The three rules are as follows; if a carbon is bonded to a double bond, then it’s counted as 1 pi electron. If the carbon has a lone pair of electrons, it is counted as 2 pi electrons. If the the carbon as a positive charge, then it is counted as 0 pi electrons. The priority of the rules follow the order in which the rules were explained earlier. For example, if a carbon was bonded to a double bond but had a positive charge, that carbon would be counted as 1 pi electron instead of 0. When a compound demonstrates 4n + 2 (n=number of pi electrons) pi electrons, then the compound is aromatic. If the compound is antiaromatic, it will exhibit 4n pi electrons. Any other number of pi electrons means that the compound is non-aromatic. In terms of stability, aromatic compounds are the most stable, non-aromatic compounds are the second most, and antiaromatic compounds are the least stable.
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