[MrTeo]

I know this is quite a common question and apparently easy to be retrieved from Organic Chemistry books... but I haven't already found any text (or even any other sort of reference) which clearly explains how can you identify a stereogenic centre in a cyclic compound and this is driving me crazy... I've checked on the Clayden-Greeves and on the Hart and found no helpful information... looking on the net I read somewhere that you should count the whole chain (except for the considered C atom) clockwise (e.g.) as the first substitutent and then consider it, taken counterclockwise, as the second substitutent. But checking on another site I found a different answer...

Could you please help me? I just need some clear and definite information about stereocentres in cyclic compounds...

Thank you all very much 

[cpncoop]

In cyclic compounds, you identify the stereocenter, and count around the ring in a clockwise or counterclockwise fashion, determine the priorities of the substitution pattern, and assign the stereochemistry.  It's identical to what you would do with an open-chained compound.  It would help if you provided an example, but the same ideas for open-chained compounds hold true here as well.

[srihari]

another way is to draw the planar view of the compound and then use the dash and wedge bonds and then check for the symmetries and decide the chirality of the carbon under discussion . this should make life simpler

[MrTeo]

Ok... Here is an example as asked, am I right? 

[stewie griffin]

MrTeo, we can't say if you're right or not since you didn't indicate any sterechemical info in your drawings. If your figure on the left you need to indicate if that methyl group is a wedge (pointing towards us) or a dash (pointing away from us). Only then can I check if it's (R) or (S). As far as the double bond goes though... we don't assign those carbons the (R)/(S) notation.

[MrTeo]

Yep, I'm still a beginner with sterochemistry and it's quite clear to see 

Here's a better one (at least I hope so)... The stereocentres are the same and the notation for the carbon attached to the methyl group should be S as I wrote... my only doubt is: when we've got a double bond and we identify the carbon atoms belonging to it as stereocentres, the only notation we need to assign is E/Z considering the substitutes's priority? Transforming the double bond in single bonds with carbon atoms it's only used when we need to find priorities?

Thank you all again 

[Schrödinger]

Hi MrTeo

That revised picture of yours... why did you put a wedge on the hydrogens?

[MrTeo]

Hi ^^

Well, I was asking myself if I had to identify the disposition of substitutents on the double bond counting the chain branches as substitutents like when I'm working on a stereocentre... 

[Schrödinger]

my only doubt is: when we've got a double bond and we identify the carbon atoms belonging to it as stereocentres, the only notation we need to assign is E/Z considering the substitutes's priority?

Yes. That is the IUPAC convention. Sometimes, you might want to use cis/trans for simplicity

Transforming the double bond in single bonds with carbon atoms it's only used when we need to find priorities?

Yup

[MrTeo]

Right... now everything's quite clear... only one last thing, regarding double bonds and E/Z (or cis/trans) convention: do I need to specify whether on a cycloalkene the substitues are on the same side or not? (e.g. (Z)-1,2-dimethylcyclohex-1-ene

[sjb]

Right... now everything's quite clear... only one last thing, regarding double bonds and E/Z (or cis/trans) convention: do I need to specify whether on a cycloalkene the substitues are on the same side or not? (e.g. (Z)-1,2-dimethylcyclohex-1-ene

Possibly best practise to, yes, but bear in mind that in smaller cycloalkenes the (E)-isomer is actually impossible due to steric grounds. I think cycloheptene is the smallest that you can observe both at room temperature for reasonable periods of time.