What stereoisomers are formed in the following reactions? Whic...

Question

What stereoisomers are formed in the following reactions? Which stereoisomer is the major product?

a. the acid-catalyzed dehydration of 1-pentanol to 2-pentene

Accepted Answer

Welcome back, everyone in the acid catalyze the hydration of one Hatin to two hapton determine the steal isomers formed. And which of them would be the major product. The starting material is one hapton. So we are simply going to draw a seven member chain, right? Because we have seven carbon atoms in the parent, and then we are going to add our alcohol group to carbon. Number one, it's really important to understand that we are starting with a primary alcohol. So whenever we perform an acid catalyze dehydration with sulfuric acid in the presence of heat, we're expecting an E two mechanism due to the fact that primary alcohols do not form stable carbo cats. So in the mechanism, we are, first of all proin our alcohol, we can state that we're getting our proin to intermediate in the first step, which is of course achieved using hydro num since sulfuric acid ionizes completely to hydro. So we're going to draw the structure of hydro num to indicate the proton donor. And now the next step, the water molecule formed will act as a base. We want to locate our beta hyen. And now we are going to remove it well done. So now we are forming our and of course, it's a terminal alkin or one heine instead of two heine. So what's actually happening here, we understand that the given alkin is not really stable and there's always a chance for a process which is called a rehydration. In other words, we still have sulfuric acid present in the solution. And the given alkin can undergo an additional electrolytic addition of a proton from sulfuric acid. So we can simply state that we once again treat it with sulfuric acid. So now we are performing the protonation stop hydrogen is added to the less substituted carbon as defined by the more cognitive because we want to form a more stable carbo ion. In this case, that would be our secondary carbo Canion. And now it is important for us to understand that we can have bond rotation. Since we have a secondary carbo Canion, we are going to draw it in another orientation because whenever a carbo is formed and we are going to think about the algae form information, this will affect stereo chemistry. So let's draw bond rotation. And what we can see is just draw our chain. But now, instead of the metal group pointing down, we will draw it, pointing up, nothing really changes. That's exactly the same carbo just see different orientation of the metal group because it's really rotating. And from here, we want to form the most stable possible. Alkin keeping in mind that this process doesn't take place fully. There will still be some fraction of one hep in the mixture, but it looks like we are going to form two additional products. Let's indicate our beta hygienes that we're going to remove those will be higher chance that will allow us to form the most stable possible alkins. Right. So we're not going to think about hyen from the metal group since we are just going to reform our previously given king. And I simply let's indicate that water, which is our base will remove those hydrogens. So now let's see what we are getting for the first structure. We're going to redraw our chain, we're going to get rid of the positive charge. And now we understand that we are getting a trans alkin because the alky groups are on opposite sides of the double mont. So let's go ahead and label it as trans. And now for the other structure, this is exactly why we wanted to take into account the bond rotation. That's because we can also form AC L king. So we're simply going to draw our double bond, right? There's a metal group pointing up and then we're going to add 1234 carbon atoms on the other end. So we're going to add our beautiful substituent. So that'll be c because the two alki groups are on the same side of the double bond. So now let's go ahead and label our products. We have our intermediate product, there is still some amount of it left. We can, we can consider it as a minor product even though the C one is more substituted, right. The substitution pattern is really important. A more substituted alkin will be predominant, but it is still minor compared to the trans one. So the trans one will be major since you may simply recall that trans alkins are more stable due to the STAIC effect. Specifically, we are reducing our STAIC effect and electronic interactions by placing our alki groups as far as possible from each other. So now we have our two minor products. Of course, this, this one is major with respect to one hept scene because it's more substituted. But the trans one is major overall because it's in trans arrangement and it's more substituted than one hept. So now let's go ahead and label our final product or the final major product, the major product will be trans two hap. Thank you for watching.

What stereoisomers are formed in the following reactions? Which stereoisomer is the major product?
a. the acid-catalyzed dehydration of 1-pentanol to 2-pentene

Key Concepts

Stereoisomerism

E/Z Nomenclature

Acid-Catalyzed Dehydration

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