I'm trying to understand how carbons are numbered in organic molecules (i.e. as in the following image).
(source: Principles of Biochemistry by Nelson and Cox, p. 532)
I've read and heard different methods, among which:
- the end of the carbon chain with the highest oxidation state is assigned the lowest number.
- the end of the carbon chain with the highest total mass is assigned the lowest number. the number of bonds is used as a kind of multiplier (i.e. O=C-OH corresponds to a total mass of O*2+C+O+H). (source: What is the convention of numbering carbon atoms in organic molecules?)
- the end of the carbon chain with the substituent of the highest atomic number is assigned the lowest number (source: Principles of Biochemistry by Nelson and Cox, p. 73).
- the carbonyl, acetal or hemiacetal carbon is given the lowest possible number (source: Carbon numbering in carbohydrates)
Phosphorous would be the highest atomic number constituent, while the remaining rules (carbonyl carbon, total mass and oxidation state) would assign the carbonyl carbon the lowest number.
I assume some are just simplifications. What is the correct method, or is there no single general one?