Two stereoisomers are obtained from the reaction of cyclopente...

Question

Two stereoisomers are obtained from the reaction of cyclopentene oxide and dimethylamine. The R,R-isomer is used in the manufacture of eclanamine, an antidepressant. What other isomer is obtained?

Chemical structures of R,R-isomer and eclanamine, an antidepressant, with labels indicating each compound.

Accepted Answer

All right. Hi everyone. So this question is saying that the reaction of cyclo hete oxide with dimeth amine forms two stereo isomers. One of them is an RR isomer. Determine the other stereo isomer found. Option A says or or is summer only option B says Sr isomer, option C says SS isomer and option D says RS isomer. Now first and foremost, recall that oxides can undergo S and two reactions relatively easily due to the strain of that three member ring in the oxide makes it relatively easy to open. So in the S and two reaction with normally the less substituted carbon or the less hysterically hindered carbon would be the one to be attacked by the Nile. But in the case of cyclo heptane oxide, what you'll notice is that the molecule has an element of symmetry to it. So the reality is right that there's no such thing as a more substituted carbon or a less substituted carbon in this case, because they both happen to be equal. So therefore, right, when illustrating our nucleic attack here diamond for a mean can attack really on either side and because this reaction can take place in either direction, you end up with two products that have different stereo chemistry associated to them. Now, for the first possibility, I'm going to go ahead and draw the arrows in blue so I can have dimethyl amine attack my first carbon, which therefore breaks the bond between carbon and oxygen to yield the following. Now, honestly, seven member rings are a struggle. So please bear with me here, but I'll do my best. Sure. But in this example, at the very least, what I did was that I drew dimethyl amine attaching itself to the first carbonatum of the oxide ring. So here is di methylamine with the positive charge because it's still attaching to the hydrogen or it still has the hydrogen. And then on the other side, the oxide oxygen is going to be on the opposite side of the ring. So here I'm drawing it as a wedge, whereas my nuc file was depicted as a dash. All right. So here after the or rather after an intermolecular or intra molecular proton transfer, the proton that's originally on the nitrogen can be transferred onto the oxygen of the starting oxide. And so that again, seven member rings are a struggle. But after that process, my nitrogen becomes neutral and that negatively charged oxygen becomes a hydroxy group instead. So this is one possibility. But my second possibility, which I'm drawing the arrows for in red features the same process. But with the nucleic attack happening on my second carbon, which results in my other carbon oxygen bond being broken instead. So here I'm going to be illustrating very similar looking or very similar looking product as the first possibility. But here I'm only switching the locations of both the amino group and the oxygen though I am still going to draw them on their respective side of the ring. So at this point, right, in intermolecular proton transfer takes place once again and we end up with our hydroxy group and the amino group both neutral this time. So now let's go ahead and talk about stereo chemistry because recall when it comes to assigning R or S configuration, the first thing you have to do is rank the attached atoms associated to the Cairo center according to the atomic weight, right. So here, if I look at the Cairo center that's bound to the nitrogen here in the first product, right, the one that was depicted in blue, then my first priority is going to be the nitrogen itself because it has a higher atomic weight than both carbon and hydrogen. So here nitrogen is my first priority. But in this case, my chiro center is bound to two carbons. However, one of them is bound to oxygen which has a higher atomic weight than hydrogen. So the carbon bound to the hydroxy group is going to take second place, whereas the other carbon is going to take fourth place. And as a result right hydrogen, which I'm drawing right now actually is going to be in fourth place because it has the smallest atomic weight. Now, before I can go ahead and actually determine serial chemistry recall that you have to rotate the molecule so that the lowest ranking atom in this case, hydrogen is facing the back of the ring or rather away from yourself. So here, what I'm going to do is I'm going to essentially flip the ring entirely to ensure that it's the nitrogen facing myself instead of the hydrogen, which it is in this case. So when I do that right, and I'm going to draw it on the bottom here is my seven member ring. And now I'm going to draw my substituents on the left side instead of on the right side to showcase that I did in fact flip this molecule. So at this point, the amino group should be depicted as a wedge, whereas my hydrogen should be depicted as a dash. So when I go ahead and I label my priorities, once again, what I'll realize is that when I go ahead and I trace in a circle, going from my first to my fourth priority, I am going counter clockwise. And because I'm going counterclockwise, my first stereo center here is in the S configuration. So I'll be marking this as an S and now we can go ahead and do the same thing with our second stereo center here with our hydroxy group directly attached to it. Now, in this carbon, right, because I have the hydroxy group, oxygen having the highest atomic weight is going to be my first priority. Now, the second serial center once again is bound to two carbons. However, one of them is connecting to the nitrogen of the amino group. So because of that nitrogen, of course, has a higher atomic weight than hydrogen. So that would break the tie. And so the carbon connecting to nitrogen is second place and my remaining carbon is third place, which once again leaves hydrogen in fourth place. But in this example, right, or for this stereo center, when I go ahead and I trace my priorities or rather my groups in order of priority or order of atomic weight, that circle also happens to run counterclockwise, which means that my second stereo center is also going to be in the S configuration and notice how this is actually going to be the other stereo isomer because the question specifies that we have an RR isomer. So what that means is that we went ahead and we actually found the second isomer to BS S. So option C is going to be our answer in the multiple choice and there you have it. So if you stuck around to the end, thank you so very much for watching. And I hope you found this helpful

Two stereoisomers are obtained from the reaction of cyclopentene oxide and dimethylamine. The R,R-isomer is used in the manufacture of eclanamine, an antidepressant. What other isomer is obtained?

Key Concepts

Stereoisomerism

Chirality

Dimethylamine Reaction with Epoxides

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