[Borek]

How do you define saturated and unsaturated compounds?

[Arkcon]

The underlying concept is pretty simple.  Just one unsaturation makes a hydrocarbon unsaturated.  But with a more specific question, we can try to get down to what's confusing you.  But you knew I was going to ask that. 

[Borek]

And you know if I am not going into specifics, that's because I don't want a skewed answer, just the first idea, the most obvious, the distilled understanding

[zsinger]

Saturated simply is defined as "All bonds which are single bond eligible are, indeed, single bonds."  I believe it leaves resonance out of the picture.
             -Zack

[Borek]

Bumр

Seriously, I was surprised by a question I was asked lately somewhere else, and checked  - IUPAC doesn't define what "unsaturated" means and people claim strange things. Strange to me that is.

Lets ignore aromatics for now. They are a separate class.

[DrCMS]

I was taught that unsaturated meant any compound with at least one C=C or C≡C.

IUPAC doesn't define what "unsaturated" means and people claim strange things. Strange to me that is.

What sort of things do other people say?

[curiouscat]

I was taught that unsaturated meant any compound with at least one C=C or C≡C.

That's the definition I'd go with.

I'm now speculating: Molecules that can be hydrogenated away (under some condition no matter how harsh) without liberation of any other smaller species.

[Borek]

Problem is with the definition "any compound containing double bonds is unsaturated".

I was always under impression that it is about carbon-carbon bonds only, and no other bonds matter. However, on another forum it was suggested that it means any double bond make compound unsaturated, or that "any compound that can be hydrogenated in unsaturated". That makes acetone unsaturated and sounds crazy. My first idea was to check what is the IUPAC definition - but I was not able to find one.

In the same discussion I was also told different books explain the term "saturated" differently - to quote OP "Clugston et.al. says one thing, Claydon et.al. say the opposite." (but I have no access to neither, so I can't check details, I just guess it should be Clayden not Claydon).

[curiouscat]

I was always under impression that it is about carbon-carbon bonds only, and no other bonds matter. However, on another forum it was suggested that it means any double bond make compound unsaturated, or that "any compound that can be hydrogenated in unsaturated".

That seems too broad. It'd make an oxygen molecule unsaturated?!

[Borek]

Well, oxygen is not an organic compound.

[Arkcon]

No, this has come up this forum before.  As an example, carbonyl groups, that is -C=O don't make a molecule unsaturated.

[Borek]

But do we have any definitive source for that?

It is not that I doubt, it is that I am looking for something that would close the discussion.

[Babcock_Hall]

Consider acetaldehyde, C₂H₄O.  2n + 2 = 6.  (6-4)/2 = 1. Therefore, I would say that it has one degree of unsaturation, and the carbonyl group is the only candidate for an unsaturated group.  However, when speaking of saturated versus unsaturated fatty acids, one always ignores the carboxylic acid, and instead one focuses on the hydrocarbon chain.  Therefore, I think that there is some ambiguity in the way the term is used.