When to number (pg.29 intro to chem textbook)

[Eman_Burney_1D]

On page 29 of the green Introduction to Organic Chemistry textbook, there is an example listed as 1,4-Cyclohexdiene. It is stated in the textbook that if there is only one possible structure, numbering is not required, and from what I got, 1,4-Cyclohexdiene has only one possible structure. So is the numbering in this case optional, or is there another possible structure that I missed? Thank you!

Also, I know for alkenes when the alkene carbon chain has 4 or more carbon atoms, then the position of the double bond needs to be given in the name. Is there a similar guideline to easily determine when the position must be given in the name for cycloalkenes?

[Chem_Mod]

For this example yes, this is the only possible structure, providing that proper IUPAC naming convention is followed.

For cycloalkenes it is necessary to identify the position of the double bond when there is another double bond, or when there are substituents. Basically, whenever there is more than just one double bond it will likely be important to specify position.

Good question.