I am curious as to why I have sometimes seen butanone, CH3CH2COCH3, labelled on bottles as 2-butanone, or butan-2-one. I realise that the 2 refers to
the position of the functional group, but I was under the impression that numbers were not used unless needed. Thus we do not refer to 1-chloroethane,
because there is only one possible isomer of chloroethane, but we do use numbers for dichloroethane because there are two possible isomers
(1,1-dichloroethane and 1,2-dichloroethane). Try as I might, I can only come up with one structural isomer for butanone, so surely the number is
superfluous. Am I missing something?12AX7 - 24-11-2006 at 13:10
How about propan-2-one (acetone)? Same thing, but they do it anyway. Redundancy I suppose.
TimNerro - 24-11-2006 at 13:41
Computerized naming mehbeh?garryb - 27-11-2006 at 01:06
Thank you for the comments. Yes, I am forced to the conclusion that it is sheer redundancy. At least no-one pointed out that there were two butanones,
and I had missed one, which is what I was afraid of. (Sorry to end that sentence with a preposition, but I can't think of any elegant way not to do
so!)
What next? Chloroform as 1,1,1-trichloromethane? Acetaldehyde as ethan-1-al?
Thank you everybody for a very enjoyable, intelligent, anfd high-quality discussion board.Blind Angel - 27-11-2006 at 01:18
Might be because it's early, but I think that there can be only one butanone since 1 and 4 butanone are in fact aldehyde and 3-butanone is a mirror of
the two, also I can see how you could stick carbon differently to make a iso , cis or trans butanone.
And about 1,1,1-Trichloromethane, some of us here call chloroform that way (see: Garage Experiment with Trichloromethan) as ethan-1-al, well that's
weird and redundant... garryb - 27-11-2006 at 01:41
Yes, there is till time for me to be corrected, but I'm now moderately sure that there is only one butanone.
Of course there is no objection to calling chloroform trichloromethane, or acetaldehyde ethanal (indeed in many circumstances it is preferable) - it
is the redundant numbers which mildly irritate me.Eclectic - 27-11-2006 at 06:48
Cyclobutanone, methycyclopropanone.
[Edited on 27-11-2006 by Eclectic]garryb - 27-11-2006 at 09:50
Good points Eclectic. I did not think of those. They would, of course, have different formulae from butanone (two hydrogens less) to allow for the
extra C-C bond required to cyclise themselves.Nicodem - 27-11-2006 at 11:48
Quote:
Originally posted by garryb
Yes, there is till time for me to be corrected, but I'm now moderately sure that there is only one butanone.
There is only one butanone but there are many butanones. There are even many butan-1-ones. For example, there is 1-phenylbutan-1-one (aka
butyrophenone by its trivial name) and so on. As you see there are reasons why to call methyl ethyl ketone as butan-2-one by IUPAC rules. It might
appear unreasonable at first glance, but when you stick to the rules you do find them useful in exceptional circumstances. It is however much better
to use trivial names whenever applicable - they are nevertheless more humane.EtaBeta - 24-1-2007 at 16:30
