Naming a ring with an alcohol group? Is it necessary to include the "1" in the name to indicate that the OH group is at the 1st carbon? Isn't it kind of assumed?

Is it necessary to name a compound "2-(3-methylbutyl)-1-cyclopentanol"?

Or is "2-(3-methylbutyl)cyclopentanol" sufficient?

Thanks!
It depends on the priority of the substituents on the ring. If the highest-priority group is the alcohol group, then the numbering of the carbons in the ring starts there - so the 1 is implicit, and you do not need to state it. See 2-(3-Methylbutyl)cyclohexanol as an example.



Note that the alkyl group position is assigned a number relative to the position of the -OH group. However, if there is a higher-priority group than -OH then the position of the alcohol will be assigned a number relative to this higher-priority group; see 2-hydroxy-3-chlorobenzoic acid.



In your example, the 1 is not necessary.