# -ene Nomenclature (semi-structural formulas)

1. May 14, 2009

### 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

2. May 14, 2009

### alxm

Yes.

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.