How would I know that if I was given trans-3-methylethylcyclohexane that this is a 1,3-trans compound? I can't find a link between the two in order to be able to translate the original iupac name to the 1,3-trans. Any help would be great!
O-Chem Nomenclature question
- Thread starter MedChad
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It's a cyclic compound and, going by nomenclature convention, it's a given that one of the substituents has to be at the 1 position, even if the "1" is left out of the name. (You have to start numbering the carbons in the ring somewhere, and the substituents must be given the lowest # possible, i.e. 1)
I think that's what you're asking, but sorry if I misunderstood your question
I think that's what you're asking, but sorry if I misunderstood your question
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so the ethyl group gets the #1 since connected to the cyclohexane (you don't number this one anymore), and you go to the 3rd carbon from that to attach the methyl group and it tells you they are trans.... so it's trans-1,3
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What is the full 1,3-trans name? Having trans/cis does not make sense cyclohexane since at best these will be different configurations and not a new isomer. Normally you see trans/cis around a double bond but you don't have one here.
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I think so since it depends on which side of the ring it is (they'll give a picture for this rather than going off the name) but I think it's more relevant to say one has to be equatorial and one axial (since trans at 1 and 3)... and most stable would have the ethyl group equatorial and the methyl axial
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But then they're neither cis- nor trans-?
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what do you mean?! if the ethyl group is equatorial, it's pointing up in the chair conformation and then methyl group will be axial and pointing down... so they are trans
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If it's equatorial, it won't be pointing straight up, but 60 degress off.
You're right, and I understand that they must be trans and what that means. But even in it's most stable form, we have no indication of whether it's RS or SR. These are two completely different molecules.
Maybe more information is required.
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yeah I know, but it think it'll still be called trans, even though it's not completely up
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Yes, I'm not sure about that either. I was checking my textbooks but they don't say anything explicitly about that case.
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I would say that's the case.
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trans-1,3 is equatorial, axial. One is up, one is down.
You know it's 1,3 because "trans-1-ethyl-3-methylcyclohexane" is redundant. You always put the highest priority substituent on the lowest possible carbon. In this case it is ethyl, and you know it's not 2,3 because then it would be named "trans-2-methylethylcyclohexane" and you know the ethyl and methyl aren't on the same carbon because then it couldn't be cis or trans and it wouldn't even have a number in it (because it would be carbon 1). You also know ethyl can't be on 4, 5, or 6 because it is a higher priority than the methyl, which is on 3.
You know it's 1,3 because "trans-1-ethyl-3-methylcyclohexane" is redundant. You always put the highest priority substituent on the lowest possible carbon. In this case it is ethyl, and you know it's not 2,3 because then it would be named "trans-2-methylethylcyclohexane" and you know the ethyl and methyl aren't on the same carbon because then it couldn't be cis or trans and it wouldn't even have a number in it (because it would be carbon 1). You also know ethyl can't be on 4, 5, or 6 because it is a higher priority than the methyl, which is on 3.
That was all the information that was given in this particular question.
so I kinda understand both sides of the discussion, but am still unsure as to how you can automatically assume the 1,3 trans.
so I kinda understand both sides of the discussion, but am still unsure as to how you can automatically assume the 1,3 trans.
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Reread above. You should know immediately that it is 1,3 just based on the name, but if you don't, you will (hopefully) be able to with practice.
Draw out ethylcyclohexane. Then throw on a Methyl two carbons away from the ethyl. Don't worry about cis and trans for now. Just draw the flat version of a cyclohexane ring with an ethyl group (anywhere you want it) and then count 2 carbons (in either direction) and add on the methyl group. Now, try to draw that same structure any other way besides 1,3. You can't do it.
Another example similar to what Pisiform said is 3-methylhexanol. You don't name it 1-hydroxy-3-methyl hexane, or 3-methylhex-1-ol.
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My orgo teacher always used to say "make a model." It was annoying in the beginning because I just wanted him to teach it to me, but after a while I started making models/drawing everything out and it really helped. From time to time I still go back to my models if I can't make sense of it on paper, but I've yet to encounter a structural problem that, when drawn, is way easier than trying to read the words without seeing the structure. If you can draw it in your head, great. If not, just scribble it down on some paper, and if that doesn't work, make a model.
Thanks for the responses guys, I was just thinking too much into it but I got it now. Its kinda simple now that I go back and think about it. I always make things harder than they really are. grrr
