Predict the major products of the following reactions, includi...

Question

Predict the major products of the following reactions, including stereochemistry where appropriate.

a. 2,2-dimethylxirane + H⁺/H₂¹⁸O (oxygen labeled water)

b. 2,2-dimethylxirane + H¹⁸O^–/H₂¹⁸O (oxygen labeled water)

Accepted Answer

everyone and welcome back in today's video, we are looking at the following problem which reads give the major products expected in each of the reactions given below. Also showed the stereo chemistry. If we examine reactions A and B, we noticed that both of them involve exactly the same ip oxide, Right? Because we have a three member drink two carbon atoms and oxygen bonded to them. And the difference between these two reactions is that in the first reaction we're using H plus with water. In the second one we're using O H minus with water. So this is as you recall an acid catalyzed reaction And the other one is the base catalyzed one. Knowing this, we are ready to proceed and we will recall several more concepts when we start writing our reaction. So if we draw our ip oxide and if we think about the mechanism of this reaction to make it completely simple for us to understand the product, we may 1st of all understand that because this is an acid catalyzed reaction. The first step in an acid catalyzed reaction is the protein nation step. So the lone parent oxygen gets protein aided by the presence of that asset. And we are getting our protein ated intermediate. We are ready to ritual our protein ated intermediate and our auction here is protein ated and has a formal positive charge because it has a total of three bombs. Now because this is an acid catalyzed reaction, you may wish to remember that an acid catalyst ring opening of epoxy eyes proceeds at a more substituted position. Notice that we have to carbon atoms that are electro filic and we are going to choose the one that is more substituted. So in particular this carbon is more substituted and we are going to choose it for our nuclear attack. Now the water molecule H. two with 18 as the mass number for auction, which implies that this is an isotope ride and we're using it to distinguish between our oxygen atoms. So the lone pair on the oxygen simply attacks that more substituted carbon. And we have the loss of the leaving group. So if you think about it and if you also amid the deportation step, right, this water will be protein ated when it forms a carbon auction bond. So we wish to d protein ated using another water molecule. So we may simply draw our original five member chain and we understand that okay, we are now forming an A wage bond at this position after the deep rotation step. So we are going to add O. H. And we are going to label this oxygen as auction with a mass number of 18. Right, this isotope. Now we have the loss of the leaving group. So in addition to that we will have one carbon atom and oh age, the original oxygen from the pox side over here. So that would be our first product for a. And we may label this as our first product. Now if we move on and actually also let's label this as a for complete clarity. And now if we move on to reaction be we have to notice that B is a base catalyzed ring opening of ip oxides. The base catalyzed ring opening takes place at a less substituted carbon. So notice that in particular we are changing the position of the nuclear filic attack and we don't have that protein nation stop if we just draw our IPAq side, The world first step is the nuclear attack itself. And we have already discussed that the nuclear attack will take place at a less substituted position. So this one instead of the previous one which was a more substituted one. So we are going to take that water molecule. My apologies. We are going to take hydroxide in this case because as the base catalyzed reaction and in particular oxygen has a mass number of 18. Once again. So the negative charge attacks that less substituted position. And simultaneously we have the ring opening. So if we think about it, We made Rachel Rachel our five member chain during the loss of the leaving group. We are forming an elk oxide and iron. So auction with a negative charge from the Ipaq side part. And now here we have a carbon atom which forms a bond with oxygen. So we may draw carbon and then oxygen. Oh a tribe, an alcohol group with and ISIS above oxygen. The word last step is the protein ation stuff. We may just use the water molecule that is present, that would protein ate it. And we may say that if we omit that step because we're not asked to show the mechanism. We are just going to say we're adding a proton and we are now ready to throw our final product. We noticed that instead of having Alcock side now we will have an alcohol group here and then the other carbon with N. O. H. And that's an isotope of oxygen. So now this is our product B. We will label it. That would be our final product B. And these are our major products regarding stereo chemistry. We don't have to worry about it because the carbon atoms are not even Cairo they have to equal ethyl groups. So we didn't really discuss concepts of a backside attack or anything. That's pretty much it right. We noticed that the products are a bit different because the longer alcohol chain with an alcohol group here has an oxygen from Depok side itself. And here it has an option from the isotopic oxygen which came as our region. So that's the main difference. Now, to conclude, the correct answer to this multiple choice question is B However, if you have any questions don't hesitate sleeved and down below in the comment section and thank you for watching

Predict the major products of the following reactions, including stereochemistry where appropriate.
a. 2,2-dimethylxirane + H⁺/H₂¹⁸O (oxygen labeled water)
b. 2,2-dimethylxirane + H¹⁸O^–/H₂¹⁸O (oxygen labeled water)

Key Concepts

Epoxide Chemistry

Stereochemistry

Isotope Labeling

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