Predict the major products of the following reactions.
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Question

Predict the major products of the following reactions.

(a) ethyl tosylate + potassium tert-butoxide

(b) isobutyl tosylate + NaI

(c) (R)-2-hexyl tosylate + NaCN

Accepted Answer

welcome back everyone. We need to determine the major substitution products formed in each of the following reactions below. So in each of the reactions. Looking at our substrates, we can see that we have this O. T. S group in each of our structures and we want to recognize O. T. S as our Tosel group. So recall that the structure of tassel and that's just a shorthand name is we have a carbon chain singly bonded to a sulfur atom which is doubly bound to oxygen atoms and then singly bound to a third oxygen atom, where that third oxygen atom has a set of three lone pairs around itself, meaning it has directly attached seven valence electrons contributing to its minus one formal charge. And we should recognize that one third of this negative charge is able to be stabilized by the following structure where we have our three oxygen atoms. And looking at this 1st 11 of the lone pairs can jump here as a double bond which would shift one of the double bonds here on this other oxygen atom as a lone pair. Or we could do the same thing in this direction to also stabilize that - charge. And it is due to this ability of this structure to stabilize extra electrons. As to why Tosel is considered a weak base. And because tassel is a weak base, it makes a great leaving group because of its ability again to stabilize extra electrons. And so now with this outlined, we also can recognize that Tosel makes an even better leaving group than what we would typically see as our alcohol hey leads in group seven A on the periodic table and that's not only due to their great stability but also due to their low reactivity and high scalability. So let's go ahead and look at example a we have our substrate structure reacting with potassium iodide and we can see that our Tosel group is bonded to a carbon that is singly bonded to another carbon. So this is a primary leaving group which signals that this is likely going to be an sN two reaction substitution. And so looking at our potassium I died recognized that potassium is a medal and ideas a nonmetal based on their position on the periodic table. And recognize that this is an ionic compound. And recall that ionic compounds dissociate to form our potassium plus carry on. And our I died an ion where because we see that negative charge on I died, we can instantly recognize it as our nuclear file and it's a strong nuclear file because it has that -1 charge. We know that our Tosel group is a good leaving group. So as it leaves the structure on its own at the same time our nuclear file in a backside attack is going to attack that carbon that are leaving group was once bound to. And this is going to create our major product where we have the following structure where ID is now bonded in the place of our leaving group and then our potassium carry on is going to bond to our task groups that will form potassium tassel. It's OK. O. T. S. As our second major product. Now we can see that where are at this carbon position that our task group is bonded to, this carbon is not a stereo center, it's not bonded to four different groups. And so we don't have an inversion product. So as we have our product written out is the correct answer here. Now let's move on to example, be where we can see that. Now we have a carbon stereo center to where our leaving group is attached to. And that's because we see we have four different groups. We have three implied hydrogen at this position. So this is a metal, we have our hydrogen, we have our tosel and then we have two implied hydrogen at this position as our fourth differing group. And so this is definitely a stereo center. And because we have a stereo center in our substrate, we should expect to have an inversion product, which is pretty typical for sn two reactions. So like before we have another ionic compound where we have sodium bonded to two nonmetal atoms where cyanide we want to recall is our poly atomic ion with a minus one charge. And then of course sodium as a plus one carry on. So cyanide would obviously make our nuclear file since it has that minus one formal charge. And as our tosel group leaves the structure because it's a good leaving group. Our nuclear file is going to attack again in a backside. Attack the carbon that are leaving group was attached to. And as we stated, our product is going to be inverted now. So we would have the following structure where we now have cyanide bonded in the place where our tosel group was but now on a wedge. And so we would have N and then see here and then our hydrogen is now going to be on a dash. This makes our inverted product. And of course we also have our sodium toluene cell phone eight. So this time it's N A O. T. S as our second major product. So now let's move on to example C here we can see we have our leaving group attached to just one carbon where this carbon is just surrounded by three hydrogen atoms. So this is a primary primary leaving group position here, which also signals another sn two reaction. And then we have the following structure that it's reacting with where sodium oxide is bonded to. This is a group. And this is particularly the isopropyl oxide or rather sodium isopropyl oxide structure where we will generate isopropyl oxide when we form the following an ion and then we would have an A plus. And so obviously our isopropyl oxide is our nuclear file here because it has that minus charge on oxygen. And so as our leaving group leaves the structure again in a backside attack. Our nuclear file is going to attack the carbon which are leaving group was bound to. So notice that each of these examples, we all had the occurrence of a backside attack. And as I stated earlier, this is exclusive to sN two reactions. And so we would form the following product which is not going to be an inversion product because we should see that we don't have a stereo center. We have three hydrogen here. So automatically this carbon is not a stereo center. So we have the following structure where oxygen is now bound to this is a group And then we have our three hydrogen for metal and the carbon of course. And then our second product yet again is our sodium tell you in Sultanate. So N A O T. S. So our final answers which are going to be these three main structures here that I'm highlighting in yellow are going to be our final answers corresponding to choice A in the multiple choice. I hope that everything I explained was clear. If you have any questions, please leave them down below and I'll see everyone in the next practice video

Predict the major products of the following reactions.
(a) ethyl tosylate + potassium tert-butoxide
(b) isobutyl tosylate + NaI
(c) (R)-2-hexyl tosylate + NaCN

Key Concepts

Tosylates

Nucleophilic Substitution Reactions (SN2 and SN1)

Sterics and Nucleophilicity

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