While numbering the longest carbon chain, in case of carboxylic functional group In some compounds i observed that the counting includes the carbon of CO2H while in other the counting starts from the next carbon.For example in,
5-oxohexanoic acid - carbon atom of carboxylic group is included. And in Pentane -1,3,5- tricarboxylic acid, carbon atoms of carboxylic groups are not included.Justify.