-ene Nomenclature (semi-structural formulas)

[Rudders]

Hi,

I was just confused as to the semi-structural formula nomenclature of -ene and -yne structures. The thing that I don't understand is the = sign in the formula.

For example:
CH₃CH₂CH=CH₂

What does that equals sign mean? Does it represent where the double bond is located?

If so, why does ethene have the structural formula CH₂CH₂ instead of CH₂=CH₂

Thanks
-Rudders

 

[alxm]

What does that equals sign mean? Does it represent where the double bond is located?

Yes.

If so, why does ethene have the structural formula CH₂CH₂ instead of CH₂=CH₂

You can write it both ways. CH₂CH₂ is the 'normal' way, whereas when you use an equal sign to represent the double bond you're approximating the structure diagram in text. Formally you should really stick to either the formula or a full and proper structure diagram, but in informal contexts it can be useful.