The main chain in organic molecules in case of the presence of functional groups

There are two types of functional groups (functions): a) The functions which are necessarly on the end of a chain, for instance: especially: b) The functions which can be attached anywhere to the chain, for instance: especially: If a function of type a) has the precedence according to the →   table of functional groups , its C atom is number 1 of the main chain and the function must not be numbered. The carbon number 2 is often designated by the greek letter α (alpha), the carbon number 2 by the greek letter β (bÍta) and so on.. 2 - ethyl - 3 - methylpentanoic acid α - ethyl - β - methylpentanoic acid