How to determine functional group?

How to circle the right amount of functional group, for example
this is what i mean

do i circle only C=C or -c=c-, that is do i only circle elements of functional group or bonds, as well?

2 Answers
Dec 17, 2016

I would say that the functional group is only the atoms of that particular group and the bonds among them. The bond that holds the functional group in place would not be considered part of the group.


Here's my rationale: when we change a functional group, we change the atoms of that group, and the bonding within the group (for instance a hydroxyl group into a carbonyl group), but we generally do not change the bond that fixed these groups in place originally.

See if anyone else answers, and hopefully you can get a consensus on this, as I never really thought about it too much before!

Dec 21, 2016

I would say it depends on the functional group. For example, as a grad student, here is how I would identify the following functional groups:

  • Ether: #-"O"-#
  • Alcohol: #-"OH"#
  • Alkene: #"C"="C"#
  • Halo: #-"X"#
  • Carbonyl: #"C"="O"#
  • Carboxyl: #-stackrel( : "O" : )stackrel(||)"C"-stackrel(..)"O":#

For instance, an ether group wouldn't be an ether group if you only circled the oxygen; it wouldn't give the context that the oxygen has two single bonds on it and two lone pairs.

Or, if you circle only the halogenic atom, it may come off as simply identifying what the halogen is, rather than saying that it is a functional group.

In general, I would simply consider whether what you circled, placed as-circled into a table with no further context, can still be identified as that functional group.