Draw the structure of and name the enantiomeric diols that res...

Question

Draw the structure of and name the enantiomeric diols that result from the cis-dihydroxylation of the alkene shown.

Chemical structure showing cis-dihydroxylation of an alkene with reagents OsO4 and NaHSO3, H2O for diol formation.

Accepted Answer

Hi, everybody. Welcome back. Our next problem says, draw and name the products of the cis di hydroxylation of the molecules shown befo below. And we have a molecule that's a six carbon chain with a ketone on the second carbon. So our carbonel group, I should say on the second carbon, it is a ketone and a double bond from carbon three to carbon four. And we see our reaction arrow above a reaction arrow. We see we have two steps. So number one OS 04 is added. And number two, we have NAHSO three and water. So we don't need to puzzle out what kind of reaction will happen here. We're told right, in the problem that we have a cyst di hydroxylation reaction. So that involves the conversion of an alkene. So we see that lets us know that it's not our carbon group. That's important to the reaction here. It's our carbon carbon double bond. We have the conversion of the alkene to a vicinal dial. So a molecule with two alcohol groups on adjacent carbons. In this case, it's the two carbons that were in the double bond. Now, each have an alcohol group added to them and it's a cyst di hydroxylation. So those two alcohol groups will be added on the same face of the double bond. And that's because of the nature of this reactant of osmium to trox side, it forms a ring, an ester ring where two of its oxygens bond with the carbons that were in the double bond and form this ring. And then we add our reducing agent which releases the ring. The oxygens are left behind on those carbons and then they're proton it. So let's draw what our product will be here. So I'll draw my six carbon chain, draw that Carbel group. Again, that's not affected by the reaction. And then on carbon three where I'd had the double bond, I had an oh group and on carbon four, another oh group, I'm going to put this in parentheses because I'm not quite done here. I drew those as straight lines, but that doesn't show the stereo chemistry here. Again, we need to remember these will be added on the same face of the double bond. So I just drew it this way because we need to think about the potential of isomers. So let's think about drawing this with stereo chemistry indicated. So again, my six carbon chain, my carbonel group, so I can draw the ohs oh let's draw the one on car three as a solid wedge. So there's my first o age group if that one's a solid wedge the one on carbon four also needs to be facing in the same direction. So I can have two wedges, but both of those groups must be the same direction. So I just have one other possibility, some draw next to it carbonel group. What should be both of those oh groups on the dashed wedges. But again, they both have to face the same way. So those are our only two possible stereo isomers. So now our question had to draw and name. So we need to think about the name of this molecule. So looking over at the molecule that I've put in parentheses without the stereo chemistry, I'm going to work over here just to keep from cluttering up the structures I've drawn with my stereo chemistry indicated I have a six carbon chain the most, they're sort of the top priority functional group here is the ketone. So I start numbering it from the side closest to the ketone this case, the left side. So 123. So I've got my ketone on carbon two, my first oh group on carbon three, my second oh group on carbon 456. So six carbon chain, my root here will be hexane. I have the ketone on carbon two. And for ketones, I indicate that with the ending one. So I'm gonna have Hexane hyphen two hyphen oone, hexane 20 That's my root molecule there. So now my alcohol groups are labeled as substituents. Now if alcohol was the most highest priority functional group, I'd have the ending OL but it's not, they get labeled as hydroxy substituents and they are on carbons three and four. So we'd say three comma four. The last thing we need is we need to indicate there are two of them. So we add the prefix dye 34 die hydroxy. So let's put it all together and our name will be 34. So three comma four hyphen die hydroxy. Oops, I accidentally put a hyphen at the end of dihydroxy and it doesn't belong there dihydroxy hexane to own. There's just one thing missing from this big long name, which is that we need to indicate the stereo chemistry with our R and S notation. So let's look at our two molecules with that indicated. Where are our chiral centers? Well, we have carbon one and carbon six are terminal carbons. So they can't be chiral centers. Car in two has the double bond to the oxygen. So that's not it, it's then carbon three does have four different groups. It has a hydrogen, it has the oh group, it has the side of the chain with the ketone and then the side of the chain with the other alcohol carbon four. So we'll put a little asterisk there to indicate it's a chiral center, carbon four, as we might suspect is also a chiral center, alcohol group hydrogen. And then the two sides of the chain carbon five has two hydrogen. So it is not. So now we just have to pick out figure out our stereo chemistry there. And for that, we'll want to draw the hydrogens on here. Both of our alcohol groups are solid wedge. So we'll go ahead and put the dashed wedge for our hydrogens. Now, in each case, the hydrogen will be the lowest priority functional group. So let's number our other functional groups by, by priority to determine whether we'll go clockwise or counterclockwise as we go in order of priority 123. So for carbon three are hydrogens in the back, that's the lowest priority. And then number one priority would be the alcohol group. Since O comes before C and priority, it's a higher atom molecular weight. And then we have two adjacent carbons, which one is higher priority. Well, our carbon on the left, don't forget we count double bonds twice. If we're the same atom, we go back to the next atom. So this carbon has bonds to. So it's a little tricky to write in here. I'm gonna write just on the top left. So I, I notate it as C and then in parentheses, I have bonds too, an oxygen, which is a double bond. So it would be o comma o every double bond, you count that out twice and then it has a bond too. Another carbon that last or that first carbon in the chain, I should say, then our other adjacent carbon on the right side. Again, it's another carbon. So we put c and an open parentheses has bonds to and oxygen and then it has a bunch of carbon. So O comma C comma and then has an H. So when we compare those two, we have OOC versus och the carbon on the left which has that car is in the carbonel group is more important. So that's going to be number one. So there's substituent one or excuse me, number two, because we already have our alcohol group as number one and in substituent three on the right side. So now to go from 1 to 2 to 3, I'm going clockwise. So this carbon three will be in the r arrangement. Now we need to look at carbon four. So I labeled the other numbers in red. I'll do this in purple to kind of keep them straight here on this atom. Also the hydrogens in the back. And our top priority will obviously be the alcohol group. That's number one. And then again, we compare our two carbons. Well, we've already labeled carbon four as having och as its other bonds and then carbon five or sorry, excuse me, getting mixed up here. It's not car I'm looking at carbon four as my chiral center. I need to look at carbon three and carbon three has OOC as its other bonds and then carbon five on the other side. But C and then in parentheses, it has a bond to one other carbon and then two hydrogen. So Chh, so there you can see that carbon three is going to be higher priority than carbon five. So we have number 10, number two is carbon three and number three is carbon five. So here to go 1 to 2 to 3, I'm going counterclockwise. So this one is going to be s so carbon four will be S so I could go through this whole process again on the second molecule. But since I'm just flipping the, the oh and the H I just know I'll have the opposite stereo chemistry on those two stereo centers. So on our other is our other isomer, the carbon three will be S and carbon four will be R and you could see how that's the case because we have our hydrogen in the front on this one. And when our least important uh group is in the ba is in the front, we'll still have that same clockwise direction. But when our least important group is in the front, that's going to be S rather than R. So sort of the shortcut there, we don't need to go through and figure that all out again. So now we have our stereo chemistry, we have our name, we have our two molecules. I'm just going to redraw them and then we'll write out the whole name just because my picture has gotten very cluttered and in terms of looking at the answer tidily, this is a little hard to read. So I will just scroll upward and sort of make a clean copy underneath. So now we've got our two products drawn out neatly. The first one with our two alcohol groups on the solid wedges facing upward. The second one with our 20 groups on the dashed wedges facing downward, both have the name 34 dihydroxy hexane two own. All we have to do is our add our notation of our stereo chemistry. So that means our molecule with the solid wedges on the left, we will put in front of the name in parentheses, three R comma four S and closed parentheses and then a little hyphen. And so then obviously our other isomer will be open parentheses. Three S comma four R lowest parentheses and hyphen. So three R 4 S3 H four dihydroxy hexane and two own and then three S four R, 34 dihydroxy hexane two own. So there we have it, we have our two stereo isomer products, those vicinal dials and we have their proper names complete with indication of their stereo chemistry. See you in the next video.

Draw the structure of and name the enantiomeric diols that result from the cis-dihydroxylation of the alkene shown.

Key Concepts

Cis-Dihydroxylation

Enantiomers

Chirality and Stereochemistry

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