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 (bêta) and so on..
2 - ethyl - 3 - methylpentanoic acid
α - ethyl - β - methylpentanoic acid