Using Table 18.3, name the α-amino acids that (a) contain an aromatic ring, (b) contain sulfur, (c) are alcohols, and (d) have alkyl-group side chains.

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All right. Hi, everyone. So this question is asking us, do the following alpha amino acids have an aromatic ring, sulfur containing group hydroxyl group or a group side chain. And here we have four different amino acids and four different answer choices proposing each type of side chain for all four of them. So first lets go ahead and recall the basic structure of an alpha amino acid amino acids contain both a carboxylic acid group and an amino group in the same molecule. But the term alpha amino acid refers to the fact that in this case, the amino group is attached to a carbon atom directly adjacent to the carbonyl of the carboxylic acid group because that is called the alpha position or the alpha carpet. And in addition to the alpha carbon in the center of our structure is a side chain otherwise known as an art group. Now, the identity and the properties of the R group R would distinguish alpha amino acids from each other. So considering the four amino acids provided, we can go ahead and identify the alpha carbon in all of them because it's the carbon that's connecting to both the carboxylic acid group and the amino group. So now that we've identified the alpha carbon, we can also go ahead and circle the side chains for each. They all happen to be all the side chains happened to be to the left side. So starting off with number one, we can see that a benzene ring is part of the side chain for the first alpha amino acid. In other words, we have a ring system that has conjugated double bonds or double bonds separated by one single bond in between them, which causes a delocalized p electron cloud. So all this is to say that the first amino acid contains an aromatic ring side chain because benzene happens to be part of our side chain. Now, on the other hand, our second amino acid contains an isopropyl group as or sing because notice how we have a three carbon substituent with the second carbon connecting to the alpha carbon of the amino acid. Now, in this case, we only have carbon carbon, single bonds as part of our substituent. Meaning for compound two, here, our side chain happens to be an a group because it is a straight chain of carbon atoms. Up next is amino acid three, where in addition to one carbon atom in the side chain, we also have this s group. In other words, sulfur connecting to a hydrogen atom at the very end of the side chain. Therefore, the third amino acid contains a sulfur containing group because there's sulfur in the structure of the side chain last but not least for part four. While amino acid four looks very similar to amino acid three. But instead of an S group, we have an O group and recall that an oh group is referred to as a hydroxyl group. So amino acid four contains a hydroxyl group as part of the side chain. Now, just for your reference, the amino acids listed here on the screen in order from one through four are phenylalanine veen cysteine. And sir, but with this in mind, we have arrived at our final answer based on the information gathered by examining the structures of each of these alpha amino acids. The correct answer is option a in the multiple choice because compound one has an aromatic ring, two has an O group, three has a sulfur containing group and four has a hydroxyl group. So with that being said, thank you so very much for watching and I hope you found this helpful.

Using Table 18.3, name the α-amino acids that (a) contain an aromatic ring, (b) contain sulfur, (c) are alcohols, and (d) have alkyl-group side chains.

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Key Concepts

Amino Acid Structure

Functional Groups in Amino Acids

Classification of Amino Acids