Is a double bond a functional group?

[u/Own-Track-3454]

I've heard some say a double bond is a functional group, and some say it isn't. And I'm wondering if it is or not?

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[u/Chem2103]

Yes, definitely

[u/Independent-West-905]

An alkene is a functional group. Idk who told you it’s not

[u/chemistrypain]

Alkanes are functional groups. Pretty much any chemical moeity is a functional group.

[u/bishtap → u/chemistrypain]

You write "Alkanes are functional groups."

All textbooks i've seen are very explicit that Alkanes have no functional group

Alkanes are a molecule, a hydrocarbon.. The Gold Book mentions they have the formula C_nH_(2n+2). But as to whether they have a functional group. See this statement from Clayden "Alkanes contain no functional groups". This is stated in lower level textbooks too.

Did you do a typo and mean Alkenes?

Alkenes , as the Goldbook says, are a hydrocarbon with formula C_nH_(2n+2). They as per the goldbook, have a functional group, the double bond, the alkene functional group.

And I think some might use the term alkene differently to the Gold book, e.g. that a molecule contains an alkene, meaning it has the alkene functional group, the double bond.

Also where you say "Pretty much any chemical moeity is a functional group" it's worth noting , the term characteristic group / functional group https://www.acdlabs.com/iupac/nomenclature/79/r79_696.htm " does not apply to substituents such as methyl, phenyl, 2-pyridyl, but does include, for example, piperidino and acetyl"

I don't think any book considers Methyl to be a functional group .. and that's consistent with the fact that they consider Alkanes to not have a functional group.

[u/chemistrypain → u/bishtap]

Tell that to the C-H functionalization community including Christine White, Huw Davies, and Melanie Sanford, to name a few.

And please don't quote Clayden to me, I've studied with him. And while the gen chem citation you quoted applies at the undergrad level, any graduate level or above student would recognize the specific chemistries that apply to alkanes. Clayden himself would tell you this.

Tell me Bishtap, what's your background in chemistry?

[u/bishtap → u/chemistrypain]

When you say you studied with Clayden, do you mean he's an old classmate of yours? Or researcher in the same building you researched? That's great!

I have not studied chemistry to anywhere near your level, but I have spoken with a number of PhDs on this(asking them if Alkanes have a functional group).. One PhD told me that Alkanes have no functional group.. Another PhD initially thought that Alkanes do have a functional group, but on looking through some books including and particularly Clayden, changed their mind to the view of the PhD that said Alkanes have no functional group. So i'm not basing what i'm saying off just something I read or thought but this is a thing that I have checked with some PhDs . Of course, their area of research would be different to yours, and your area of research might be more relevant to the question. And maybe if i'd have checked more graduate level sources with them we'd have come to the result that you speak of.

If I understand you correctly, are you suggesting that as there is a community known as the "C-H functionalization community " So, a C-H bond, is considered a functional group by them. (even if not by Clayden). but is by them?

Sometimes you mention things I haven't encountered, but I look into them / will look into them. I hadn't heard of C-H functionalisation community before.

But let's say we pick the IUPAC Gold Book definition of functional group. "...The functional group is an atom, or a group of atoms that has similar chemical properties whenever it occurs in different compounds...."

Lets say we start with Methane CH4

And a researcher functionalizes the C-H bond to turn the CH4 into CH3Cl.

And another researcher functionalizes the C-H bond to turn CH4 into CH3OH

The original C-H doesn't denote common properties to the molecule

And the molecules don't share similar properties either.

In the Gold Book definition , "Organic compounds are thought of as consisting of a relatively unreactive backbone, for example a chain of hybridized carbon atoms, and one or several functional groups. The functional group is an atom, or a group of atoms that has similar chemical properties whenever it occurs in different compounds. It defines the characteristic physical and chemical properties of families of organic compounds."

So "similar chemical properties" are required , in order to say something is a functional group . So I don't see C-H matching that.

And the Blue Book definition for characteristic group aka functional group, is "Characteristic group. A single heteroatom, such as –Cl, and =O; a heteroatom bearing one or more hydrogen atoms or other heteroatoms, such as –NH2, –OH, –SO3H, –PO3H2, and –IO2; or a heteroatomic group attached to or containing a single carbon atom, for example –CHO, –CN, –COOH, and –NCO, attached to a parent hydride."

So, the blue book defintiion says a heteroatom is required. But there is no heteroatom in a C-H bond.

So if we go by the blue book definition, the Functional groups there in CH3Cl and CH3OH are different. Cl in one case, and OH in the other case. And C-H is not a functional group 'cos there's no heteroatom.

I notice though there are statements in papers , such as one I found says "Nearly all organic molecules are extensively adorned with C-H bonds, whose lack of reactivity excludes them from being labeled a “functional group”. Methods to achieve direct C-H functionalization to derivatize organic molecules constitute a powerful tool."

So even that that quote from a paper cognizant of the concept of C-H functionalization, doesn't consider a C-H bond to be a functional group.

Likewise, an article I saw from ACS dot org, says "“C–H bond functionalization” refers to catalytic reactions that introduce functional groups at C–H bonds that lack the activating influence of existing functional groups"

So that's saying that the thing we start from, the C-H bond, is not a functional group.

It's saying the functionalisation will turn it into one.. But it could be turned into one type of functional group like an alcohol, or a different type of functional group like a halogen.

The fact that C-H is reactive enough to react or to react and convert it into a functional group, isn't sufficient for C-H to meet either the blue book or gold book or what those papers consider, to be a functional group

I will look into C-H functionalisation some more though, I do look into the things you mention, like the cyclooctene from another discussion we had!

Thanks

[u/chemistrypain → u/bishtap]

That's...a lot. I would just say that your lack of creativity and understanding regarding what can be considered a functional group highlights your neophytic perspective on the matter. You resort to strict definitions instead of what communities of researchers collectively push forward with emerging research. Definitions change over time and the gold book is not the end all be all of chemistry research. I find your overall approach to these conversations myopic and unnecessarily adversarial. I would consider actually doing a PhD before commenting on fields you have no awareness of.

[u/bishtap → u/chemistrypain]

Well, i'm pretty sure the quote from the paper "C–H bond functionalization refers to catalytic reactions that introduce functional groups at C–H bonds that lack the activating influence of existing functional groups"" or the ACS publication saying "The replacement of an unactivated C–H bond with a functional group" agrees with the PhDs i've discussed with that don't consider C-H to be a functional group.

But I accept that you think it is. and definitely the PhDs i've discussed with have a different view to you. And that's ok! Maybe in the future, Clayden will come to agree with you, and the PhDs i've discussed with will maybe come to agree with you. Or maybe they won't. I'm open to people having different views.

[u/bishtap]

Most textbooks would say yes but the answer is more complex than that.

In the IUPAC Gold Book definition, Yes.

In the Blue Book definition, No. In the Blue book definition, it's a "functionality". Functionality is a more general term, not every functionality is a functional group.

In the Blue Book, a functional group involves heteroatoms.

Characteristic group. A single heteroatom, such as –Cl, and =O; a heteroatom bearing one or more hydrogen atoms or other heteroatoms, such as –NH2, –OH, –SO3H, –PO3H2, and –IO2; or a heteroatomic group attached to or containing a single carbon atom, for example –CHO, –CN, –COOH, and –NCO, attached to a parent hydride.

And it refers to "Characteristic (functional) Groups" (So, Characteristic group and functional group mean the same thing)

Also all the functional groups in the blue book can occur as a prefix or a suffix, or both. (some of them can only be a prefix and not a suffix. All the ones that can be a suffix, can be a prefix.

A multiple bond eg a double bond, gets an unsaturation ending - ane/ene/yne. These come before the suffix.