Pentoses also exist in a ring form, but they most commonly occ...

Question

Pentoses also exist in a ring form, but they most commonly occur as furanose rings. D-Ribose exists in its furanose ring form in the nucleic acid RNA. Using the structure of D-ribose from Table 6.1, draw the furanose form of β-D-ribose.

Accepted Answer

Hi, everyone. And welcome back. Our next problem says, ptosis most commonly occur as furino rings using the structure of D xylose shown below. Draw the furino form of beta D Xylo Furano. And we've got our straight chain structure of D xylose, an aldose. So that carbon one is an aldehyde. And then if we number our carbon tier, carbon two has a hetero group on the right. Carmen three on the left. Carmen four on the right. And then carbon five is just the C H2O H group. So the formation of the furino furino rings are five membered rings. But since we have this oxygen that will be within the ring, one of our carbons will be left out. So the best way to remember how that should be drawn is we turn our structure on its side, the carbon one over to the right with its uh aldehyde group, then carbon five with that C H2O H group on the left side. So that's carbon six carbon one and put lines for our internal carbons and put our hydroxyl groups in the right place. So the hydrox groups are on the right that o age group is down. If the hydroxyl groups on the left as on carbon three, that oh group is up. And then with those in mind, we imagine our ring forming, imagine our tail here of the scatter pillar, the six wrapping around and coming up and then see how the carbon carbon will react with that. Oh group. So as we draw the spring forming, we draw remember in a five membered ring, our oxygen will be up at the top but we haven't formed the ring yet. So instead at the top, we're going to have our carbon carbon or excuse me, not our carbon carbon, our carbon five, which is the one that's going to react to the oh group on carbon five is going to react with that carbon carbon. So this is carbon six up on this tail here. C h2o H than carbon five. On the left side, we know that it's number of carbons here. And oops I just realized out of habit, I called that last carbon carbon six, but it should be carbon five there. So now carbon four on the left side of my ring is going to have an oh group going down. Now going down to make the bottom part of my ring that is going to. So we have carbon six or rather a carbon five. I do seem to keep wanting to make that a six carbon molecule we get so used to glucose. That's carbon five carbon four has the oh group going down. Carbon three has the oh group going up and draw our bottom up. That's going to be carbon two. On carbon two, our oh group is going down and then here's our carbonel group. So on carbon one and note that of course, whenever we're dealing with ad sugar as the sugars in our body are with that oh group pointing down on the last stereo center, you are always going to have to rotate that those groups around that bond 90 degrees clockwise to get our hydroxyl group up to where it would react. And that puts that C H2O H group above the ring. So something just to note if you're dealing with ad sugar that um C H2O H group at the end, if that's sticking up out of the ring will be sticking up. So we'll draw our ring here. Now has an oxygen at the top. It's a Pantos. So we have oxygen as one member we're going to have on the left hand side, which is now carbon four, we have AC H2O H group coming up out of the plane of the ring. Now we keep going around the ring. Carbon three has an oh group pointing up carbon two pointing down and now around carbon one are anomic carbon. And we know that that oh group can end up being on the top or on the bottom, depending on which direction the reaction attacked on So let's just draw it going up. It's now on the same side of the ring as our CH two H group. And when that is the case, so when we look at that reference carbon for where that group is, when they're on the same side, I think same begins with S which is a consonant like B or beta, this is going to be the beta animal. And then if I duplicate this five membered ring because we did have. So when I look at this new ring, I know I just need to put, finish my hydroxyl groups, I need to put that hydroxyl group on carbon one, two point down. So it is opposite that C H2O H group on the ring. So opposite begins with a vowel like A or alpha. So this is the alpha animal. So we have our answer for beta form which is what we're looking for of beta D Xylo Furino with our A oh group pointing up. See you in the next video.

Pentoses also exist in a ring form, but they most commonly occur as furanose rings. D-Ribose exists in its furanose ring form in the nucleic acid RNA. Using the structure of D-ribose from Table 6.1, draw the furanose form of β-D-ribose.

Key Concepts

Furanose Structure

d-Ribose

Beta Anomer

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