What are the rules for choosing main branch?
Identification of the parent hydrocarbon chain. This chain must obey the following rules, in order of precedence:
- It should have the maximum number of substituents of the suffix functional group. By suffix, it is meant that the parent functional group should have a suffix, unlike halogen substituents. If more than one functional group is present, the one with highest precedence should be used.
- It should have the maximum number of multiple bonds
- It should have the maximum number of single bonds.
- It should have the maximum length.
I don't understand how 3 and 4 differ. Which single bonds are we counting? Only carbon-carbon single bonds in the main chain, right?
Also, I heard there is a rule that says if you've two equal length chains, then choose the more substituted one. Why is it not given here?
And now now imagine you've two choices for a chain, like this:
The chemdoodle program gives the name as 2-(1-Hydroxybutyl)-3-methylhexanoic acid .
I simply do not understand why the methyl substituted chain is chosen instead of hydroxy substituted one and how that fits with IUPAC rules given in Wikipedia.