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Paper 1 Chemistry Question

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Wondering if anyone can answer the following question, and the explanation behind it, as I have trouble differentiating between isomers for cycloalkanes.

Thank you!

cyclo.png

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For questions like this, I like to just draw out all possible isomers and count them up.  My sketches of all isomers are in the attached file.  Remember that you can't rotate around rings, so cis and trans isomerism apply here.  Mind you, I don't know if you need to consider stereoisomers, as it just says isomers - I'm pretty sure the markscheme didn't consider them, but might be a good idea to check.  

I don't really like these questions to be honest - I'm always worried that I forgot an isomer somewhere.  

Sketch thing.pdf

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2 minutes ago, SC2Player said:

For questions like this, I like to just draw out all possible isomers and count them up.  My sketches of all isomers are in the attached file.  Remember that you can't rotate around rings, so cis and trans isomerism apply here.  Mind you, I don't know if you need to consider stereoisomers, as it just says isomers - I'm pretty sure the markscheme didn't consider them, but might be a good idea to check.  

I don't really like these questions to be honest - I'm always worried that I forgot an isomer somewhere.  

Sketch thing.pdf

Thanks for the sketch – the answer is indeed 5 isomers. 

I agree with you – though cis-trans isomerism is still stereoisomerism, it would be great if they also at least hint on whether or not E/Z isomerism is required. 

 

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Huh, I somehow forgot that cis-trans is classified as stereoisomerism - I need to review this.  E/Z isomerism is pretty similar to cis-trans isomerism actually, it's just good for more ambiguous cases.  I was thinking more along the lines of enantiomers: one of the isomers (illustrated in the attached file) does have two enantiomers, so there should actually be 6 ring isomers in total (checked on Google, which confirms this on multiple sites).  Kind of weird that apparently you need to consider cis-trans but not enantiomers.  

Another Sketch Thing.pdf

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