Is this cis or trans?

[paingains]

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I strongly believe this is cis but a colleague of mine is vehement that it is trans because of the "longest continuous chain". I thought cis was when you had two identical substituents on opposite sides in the same direction on an alkene double bond? I understand that it is E, but I dont understand why it is trans and not cis.

http://postimg.org/image/bfvrx6fr1/

 

[donovank730]

hmm

 

[csx]

Im curious as well. I feel like i should know this...

 

[PlasticBag]

I think cis and trans involve only unrestricted rotation, ie single bonds only. So you can't have cis or trans across a double bond, only E or Z.

But then, i barely passed Orgo I so... 😉

 

[nonamechemist]

Cis and trans are used to describe the relative orientation of two functional groups. In this case, you can say that the methyl groups are cis to each other; methyl group on the left and the ethanol on the right are trans to each other. Therefore, the e-z system is employed for nomenclature to get around this ambiguity in the cases of more complicated compounds. The highest priority group on the two sides are alcohol and methyl, respectively, so the name should be something like (E)-3-methylpent-3-en-2-ol.

 

[wdoc]

I agree with nonamechemist, in this case the cis/trans naming system isn't appropriate. Instead, use the E/Z naming system where the molecule you showed us is E.

 

[baxt1412]

i echo the last couple of responses.

neither.

 

[Cawolf]

(E)-3-Methyl-3-penten-2-ol

 

[ymartino]

I'm pretty sure it is trans or E since the groups have different substituents (and cis and trans are indeed involved with double bonded atoms...) http://www.chemguide.co.uk/basicorg/isomerism/geometric.html

 

[paingains]

I'm pretty sure it is trans or E since the groups have different substituents (and cis and trans are indeed involved with double bonded atoms...) http://www.chemguide.co.uk/basicorg/isomerism/geometric.html

Thanks for all the responses.

How do the groups have different substituents? the 4 substituents in all are: methyl, hydrogen, methyl, and ethanol. I clearly see two identical substituents and for this reason would say its Cis. If I were asked Z or E straight up, I would say E. if I were asked cis or trans straight up, I would not say trans, unless two identicals are trans to one another. Cis and trans are a way of comparing substituents.

You don't just say the whole thing is cis or trans (even though you are technically doing this when you name it), but instead you would say X substituent is cis/trans to X substituent.

Cis and trans are used to describe RELATIVE stereochemistry, whereas E/Z is the absolute method. I clearly see two relative substituents and would thus say the METHYLS are CIS to one another. Anyone else please reason with or against this because its driving me nuts

 

[SN2ed]

Thread closed. These types of questions belong in the MCAT Study Q&A forum only.