Identify the D/L and R/S configuration of all of the following...

Question

Identify the D/L and R/S configuration of all of the following monosaccharides:

Structures of four monosaccharides for D/L and R/S configuration identification.

Accepted Answer

So this practice problem says, identify the DL and RS configuration of all of the following monosaccharides, and notice that we've got these 4 monosaccharides shown down below. Now at first glance, maybe this practice problem seemed kind of long and challenging, because maybe you interpreted this problem as saying, determine the DL and RS configuration of every single chiral carbon that's present, but that is not what this practice problem wants us to do. Instead, it's asking us to determine the DL and RS configuration of the following monosaccharides as a whole. And so recall from our last lesson video that an entire monosaccharide as a whole will take the same configuration as the one chiral carbon that's furthest away from the carbonyl group. And so what that means is that for each of these 4 monosaccharides below, we only need to determine 1 chiral carbon configuration to get our answer. And so that being said, let's take a look at our first sugar over here and notice that this sugar is in standard Fischer projection. Its carbonyl group here, which is a ketone group, is, as close to the top as it can possibly be. So it is towards the top and the longest carbon chain is indeed vertical. And so, also notice that this sugar here only has 1 chiral carbon, which makes our job much much easier. And that chiral carbon is right here. And notice that the hydroxyl group is pointing to the right of the Fischer projection which means that this chiral carbon is taking a d configuration. So we can put deconfiguration up above and also recall from our last lesson video that usually in most circumstances in our course, the configuration is going to translate to our configuration. And so we can also put our configuration here. But you could have also used the con angle pre log system on this chiral carbon to determine that it has our configuration. But that is the answer to part a. So moving on to our next sugar here, notice that the carbonyl group is hidden in this aldehyde group here at the top. And so the chiral carbon that's furthest away from this carbonyl group would be this chiral carbon right here. And so notice that the alcohol group of this chiral carbon is pointing to the left of the Fischer projection which means that the chirocarbon has L configuration. So, we can put L up here at the top and also recall from our last lesson video that usually in our course, l configuration will translate to s configuration. But again, you could have also used the Con Ingle pre log system rules to determine that this chirocarbon has S configuration. But really that is the answer to part b here, so let's move on to part c. And again you can see that here we have our carbonyl group present as a ketone group and the chiral carbon that is furthest away from this carbonyl group is not not going to be this carbon here because notice that this carbon is not chiral since it has 2 hydrogens bound to it. Instead, the carbon that the chiral carbon that is furthest away will be this carbon here whose hydroxyl group is pointing to the right, meaning that this is going to have a deconfiguration. So we can put deconfiguration here and as we already mentioned, deconfiguration translates to our configuration in most circumstances here. But again, we could have used the con angle pre log system rules on this chiral carbon to determine that this is our configuration. And so this is the answer to part c. And so last but not least, we have part d here and notice that it's carbonyl carbon atom is hidden in this aldehyde group here at the top. And so the chiral carbon furthest away from the carbonyl group will be this chiral carbon here. And notice that the alcohol group of this chiral carbon is pointing to the left of the Fischer projection which means that this chiral carbon has an l, configuration. So we can put l at the top. And again, usually in most circumstances, l configuration will translate to s configuration, in our course. And, again, we could have also used the con angle pre log system rules to determine that this chiral carbon has s configuration. And so, these are the answers here to, our practice problem and that concludes this practice so I'll see you guys in our next video.

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Identify the D/L and R/S configuration of all of the following monosaccharides:

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