[ve_90]

According to IUPAC nomenclature, following the official rules, is the correct name of this cycloalkene: 3-chloro-4-methyl-1-cyclohexene or 3-chloro-4-methylcyclohexene? In other words, should the position of the double bond always be specified, or can it be omitted since the position of the double bond is implicit in the name and can be inferred from the positions of the substituents we indicate?

[Hunter2]

First it's not a cyclohexene, it's a cyclopentene.
The 1 at the doublebond is not necessary, because if the double bond is at other position the numbers for the substituents will also change.

https://pubchem.ncbi.nlm.nih.gov/compound/3S_-3-Chloro-4-methylcyclopentene