# Structural formulae of cyclic alkanes/alkenes? **URL:** \ **Category:** Factual Questions\ **Created:** [March 8, 2003, 12:30pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900 "2003-03-08T12:30:38Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![pretend\_my\_name\_is\_witty](https://avatars.discourse-cdn.com/v4/letter/p/b9e5f3/32.png) [@pretend\_my\_name\_is\_witty](https://boards.straightdope.com/u/pretend_my_name_is_witty)\ **Post date:** [March 8, 2003, 12:30pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/1 "2003-03-08T12:30:38Z")
I’m currently doing a module on organic chemstry in my chemistry As level, and I’m trying to work out how to write the structural formulae of cyclic alkanes/alkenes. For example, the structural formula of 2,3 dibromobut-2-ene is CH[sub]3[/sub]C(Br)=C(Br)CH[sub]3[/sub]. Or the strucutral formula of 2-chlorobutane is CH[sub]3[/sub]CHBrCH[sub]2[/sub]CH[sub]3[/sub]. However, I dont know how I’d write the structural formula of a cyclic alkane/alkene. I can draw the _given_ formula: **Cyclohexane** : ```auto CH[sub]2[/sub] / \ / \ H[sub]2[/sub]C CH[sub]2[/sub] ¦ ¦ ¦ ¦ H[sub]2[/sub]C CH[sub]2[/sub] \ / \ / CH[sub]2[/sub] ``` Oooh, that took a long time, and it still looks kinda crappy but you get the idea. I can’t think how you’d indicate that it’s a cyclic alkane when you write the structural formula. The structure is (CH[sub]2[/sub])[sub]6[/sub] (obviously it would be more complicated if it were a cycloalkene or a halocycloalkene), but I can’t think how to indicate that it’s cyclic. Is there a way to do this? Or should I just write the given formula instead? Someone please help me! ---
**Author:** ![ChalkPit](https://avatars.discourse-cdn.com/v4/letter/c/a88e4f/32.png) [@ChalkPit](https://boards.straightdope.com/u/ChalkPit)\ **Post date:** [March 8, 2003, 2:05pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/2 "2003-03-08T14:05:50Z")
> [@](#): > > (obviously it would be more complicated if it were a cycloalkene or a halocycloalkene) Well, obviously ! Ummm…if ever there was a question I have absolutely NO idea about, this is it. Move on to aromatic hydrocarbon bonding, then come back to this… ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [March 8, 2003, 2:22pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/3 "2003-03-08T14:22:52Z")
C[sub]6[/sub]H[sub]12[/sub] is good enough. Try drawing another cyclic or non-cyclic structure with the same formula. ---
**Author:** ![mnemosyne](https://avatars.discourse-cdn.com/v4/letter/m/c4cdca/32.png) [@mnemosyne](https://boards.straightdope.com/u/mnemosyne)\ **Post date:** [March 8, 2003, 3:18pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/4 "2003-03-08T15:18:05Z")
It isn’t usually needed - most lists will have the full name (think Aldrich ordering catalogue) as well as the structural formula. Being able to write this out is a good way to begin to understand the basics of the structures, and about isomers, etc, but it isn’t really fundamental to organic chemistry in terms of the _chemistry_, you know? I _think_ I might have seen it shown as c-C6H12 or something, but that doesn’t really work either, because a methyl-cyclopentane has the same formula, and besides, it isn’t accepted nomenclature (neither common nor IUPAC). The ONLY way to indicate for certain what the true formula is would be to either draw it out (with stereochemistry where appropriate), or use a completely proper IUPAC name, although most people haven’t bothered to learn all of the notation for that. ---
**Author:** ![pretend\_my\_name\_is\_witty](https://avatars.discourse-cdn.com/v4/letter/p/b9e5f3/32.png) [@pretend\_my\_name\_is\_witty](https://boards.straightdope.com/u/pretend_my_name_is_witty)\ **Post date:** [March 8, 2003, 3:31pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/5 "2003-03-08T15:31:25Z")
> [@](#): > > \*Originally posted by ChalkPit \* > \*\*Well, obviously ! > > Ummm…if ever there was a question I have absolutely NO idea about, this is it. > > Move on to aromatic hydrocarbon bonding, then come back to this… \*\* Well, I’d drawn out the given formula, and went on to write what I thought the structural formula might be, and realised that I’d picked a crappy alkane, as it has a really simple structural formula! Ok, it’s for writing out a reaction, and showing the isomers. I’ve just realised that with such a formula, I wouldn’t be able to differentiate between _cis_ and _trans_ isomers anyway. I’ll just draw the given formula, which I was trying to avoid since I’m doing this in word and hate wordart! Thanks everyone, I’ll get on with this now then… ---
**Author:** ![pretend\_my\_name\_is\_witty](https://avatars.discourse-cdn.com/v4/letter/p/b9e5f3/32.png) [@pretend\_my\_name\_is\_witty](https://boards.straightdope.com/u/pretend_my_name_is_witty)\ **Post date:** [March 8, 2003, 3:40pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/6 "2003-03-08T15:40:55Z")
> [@](#): > > \*Originally posted by Squink \* > \*\*C[sub]6[/sub]H[sub]12[/sub] is good enough. Try drawing another cyclic or non-cyclic structure with the same formula. \*\* Actually, I drew C[sub]6[/sub]H[sub]12[/sub] because it was easy to do in ascii art. The one I wanted it for has the formula would be [start ring]CH[sub]2[/sub]CH[sub]2[/sub]CH[sub]2[/sub]CH[sub]2[/sub]C(CH[sub]3[/sub])=CH[end ring], the chemical formula for which would be C[sub]7[/sub]H[sub]12[/sub] which is a bit ambiguous. ---
**Author:** ![pretend\_my\_name\_is\_witty](https://avatars.discourse-cdn.com/v4/letter/p/b9e5f3/32.png) [@pretend\_my\_name\_is\_witty](https://boards.straightdope.com/u/pretend_my_name_is_witty)\ **Post date:** [March 8, 2003, 3:43pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/7 "2003-03-08T15:43:27Z")
damnit, forgot the name of it, it’s called 1-methyl hex-1-ene, which you all knew of course, but I just thought I’d put it in anway. Another thing, which is more important, to give the side chain the lowest carbon number or the double bond the lowest number? It doens’t matter in this case, and I’m sure it’s in my notes somewhere, I just can’t find it. ---
**Author:** ![pretend\_my\_name\_is\_witty](https://avatars.discourse-cdn.com/v4/letter/p/b9e5f3/32.png) [@pretend\_my\_name\_is\_witty](https://boards.straightdope.com/u/pretend_my_name_is_witty)\ **Post date:** [March 8, 2003, 3:45pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/8 "2003-03-08T15:45:20Z")
Grrr, preview…remember to preview. That should read: **Another thing. Is it more important to give…** Otherwise it sounds totally wrong, like I’ve got some heirarchy of question importance. ---
**Author:** ![Mr.Matthew](https://avatars.discourse-cdn.com/v4/letter/m/e480ec/32.png) [@Mr.Matthew](https://boards.straightdope.com/u/Mr.Matthew)\ **Post date:** [March 8, 2003, 4:49pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/9 "2003-03-08T16:49:37Z")
> [@](#): > > \*Originally posted by Pretend My Name Is Witty \* > \*\*I’ll just draw the given formula, which I was trying to avoid since I’m doing this in word and hate wordart! > > Thanks everyone, I’ll get on with this now then… \*\* I’ve used a program called ISIS/Draw in the past and have found it very useful for the sort of chemistry graphics you wish to use. It’s no fee for academic and personal use. [ISIS/Draw: Chemically Intelligent Drawing Package](http://www.mdli.com/downloads/isis.draw/isisdrawreg.html) Hope that helps. Good luck with your studies. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [March 8, 2003, 8:09pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/10 "2003-03-08T20:09:12Z")
> [@](#): > > \*Originally posted by Pretend My Name Is Witty \* > \*\*Actually, I drew C[sub]6[/sub]H[sub]12[/sub] because it was easy to do in ascii art. The one I wanted it for has the formula would be [start ring]CH[sub]2[/sub]CH[sub]2[/sub]CH[sub]2[/sub]CH[sub]2[/sub]C(CH[sub]3[/sub])=CH[end ring], the chemical formula for which would be C[sub]7[/sub]H[sub]12[/sub] which is a bit ambiguous. \*\* Well, just plain formulae are always a bit ambiguous. You don’t know whether a molecule is cyclical, or branched, or where double bonds are, or any of that just from the formula. That’s why they also use IUPAC nomenclature. ---
**Author:** ![big\_alex](https://avatars.discourse-cdn.com/v4/letter/b/e56c9b/32.png) [@big\_alex](https://boards.straightdope.com/u/big_alex)\ **Post date:** [March 8, 2003, 8:38pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/11 "2003-03-08T20:38:10Z")
Man, either I’ve forgotten everything in the last year, or your work is much harder than mine ever was! ---
**Author:** ![Sigene](https://avatars.discourse-cdn.com/v4/letter/s/df788c/32.png) [@Sigene](https://boards.straightdope.com/u/Sigene)\ **Post date:** [March 9, 2003, 4:57am UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/12 "2003-03-09T04:57:31Z")
I’ve seen something along these lines before CH2CH2CH2CH2CH2 |\_\_\_\_\_\_\_\_\_\_\_\_| Or even CH2CH2CH2CH2CH2 |_ **O** _| Is that what your looking for? ---
**Author:** ![Shade](https://avatars.discourse-cdn.com/v4/letter/s/2bfe46/32.png) [@Shade](https://boards.straightdope.com/u/Shade)\ **Post date:** [March 9, 2003, 12:03pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/13 "2003-03-09T12:03:49Z")
At school we used something like cyclo-C[sub]6[/sub]H[sub]12[/sub], which I was never happy with at the time, but is clear and short. Do you have to use _the_ right answer, or is it ok if it’s clear what chemical you mean? When explaining the chemical to us you said: [start ring]CH2CH2CH2CH2C(CH3)=CH[end ring], Maybe something like that? ---
**Author:** ![pretend\_my\_name\_is\_witty](https://avatars.discourse-cdn.com/v4/letter/p/b9e5f3/32.png) [@pretend\_my\_name\_is\_witty](https://boards.straightdope.com/u/pretend_my_name_is_witty)\ **Post date:** [March 9, 2003, 5:12pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/14 "2003-03-09T17:12:24Z")
> [@](#): > > \*Originally posted by Sigene \* > \*\*I’ve seen something along these lines before > CH2CH2CH2CH2CH2 > |\_\_\_\_\_\_\_\_\_\_\_\_| > > Is that what your looking for? \*\* That seems to make sense, thanks **Sigene** > [@](#): > > _Originally posted by Mr. Matthew_ > > I’ve used a program called ISIS/Draw in the past and have found it very useful for the sort of chemistry graphics you wish to use. It’s no fee for academic and personal use. > > ISIS/Draw: Chemically Intelligent Drawing Package > > Hope that helps. Good luck with your studies. Excellent, I just downloaded the program and it looks really helpful! Thanks for point it out **Mr. Matthew** ---
**Author:** ![Mr.Matthew](https://avatars.discourse-cdn.com/v4/letter/m/e480ec/32.png) [@Mr.Matthew](https://boards.straightdope.com/u/Mr.Matthew)\ **Post date:** [March 9, 2003, 6:10pm UTC](https://boards.straightdope.com/t/structural-formulae-of-cyclic-alkanes-alkenes/159900/15 "2003-03-09T18:10:14Z")
You’re welcome. My karma is now balanced out from the unfortunate incident last week where I told my baby girl to turn the page in the book we were reading and she got a paper cut. Oh the horror!