Formulas for (un)saturated fatty acids?

So an unsaturated fatty acid looks like this:

H-(CH2)n COOH

This is a worm consisting of n CH2 components, which has an H atom on the left and a carboxyl group (COOH) on the right.

That’s why your first formula is also slightly erroneous. There’s no left H atom. Right would be:

Saturated: CnH(2n+1)COOH

2H atoms are now subtracted for each double bond:

Simplely unsaturated: CnH(2n-1)COOH

Double unsaturated: CnH(2n-3)COOH

Triple unsaturated: CnH(2n-5)COOH

Four times… etc.

But what do I start with it?

You can now say with the help of these formulas for each fatty acid how often unsaturated it is:

Oleic acid = C17H33-COOH

=> The expert now recognizes the formula that oleic acid is simply unsaturated, i.e. has only exactly one C-C double bond.

What do I need that for?

This is a philosophical question now. If you want to take a degree examination in chemistry, this knowledge would be very helpful in natural chemistry. Chemistry abitur can be done, but you don’t have to. That is why: A real school degree or an Abitur with Sport-LK can also be fulfilling. If you will have regained the sound knowledge of fatty acids and their structure once in your life, you will be able to answer valids at the earliest when you enter the retirement age. 😉

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VG