Pg. 101 in the course reader

[Priscilla Tamborini 1B]

On page 101 why is the molecule named 4-chloro-2-butanol instead of 4-chloro-1-butanol? How can the numbering of the carbons change when naming the substituent and the functional group? And what does his note mean by the "functional group determines the number of carbon"?

[Paul_Ajodha_2K]

In this case you're still counting the longest carbon chain which is 4 carbons and it's called 4-Chloro-2-Butanol because the functional group appears on the 2nd carbon in the chain. The functional group is going to take priority over the halogen so the smallest possible number in relation to the carbon in which the alcohol falls upon here would have to be 2.