Which of the molecules shown in question 5 has an asymmetric carbon? Which carbon is asymmetric?

Question

Two molecular structures: left with no asymmetric carbon, right with an asymmetric carbon at the second carbon atom.

Accepted Answer

Welcome back. Our next question says. And the structure of three inning the asymmetric carbons are attached to the following functional groups. Except that except reminds us that one of these functional groups were looking for the one that is not attached to an asymmetric carbon. So let's recall it. Carbon makes four bonds arranged in a tetrahedron shape. An asymmetric carbon is one in which each of these bonds is to a different atom or group of atoms. That group is important because say if one of these is to a methane and one of these is to a car box cell, even though these two bonds are each to a carbon atom that carbon atoms in a different environment. So if for instance we had like an O. H. Group over here, an H. Group here. This would be a symmetric because these are not the same exact environment for those two carbons. So let's look at our molecule here and determine which of the carbons are asymmetric. So it kind of helps to expand the structure a little bit. Here's our hydroxyl group with that carbon here. It's got a methane group bonded on the top and then it continues the chain over here to another carbon. We know carbon has four bonds. That fourth bond must be a hydrogen. Let's go to the next carbon in the chain. It's got an amino group bonded to it and then it continues the chain over here to another carbon must have four bonds. So again we've got a hydrogen. As the fourth thing there. The last carbon in the chain here is part of car boxes group with a double bond to oxygen and an O. H. On the other end. So let's look at each of our carbons and see if they are asymmetric. So our first carbon here on the top is part of the methane group. It's got three hydrogen attached to it. Those are identical. So that is not a symmetric and we can eliminate that carbon. Let's look at our next one here. It's got a methane group at one bond. Hydroxide is the second hydrogen is the third and this carbon with an amino group next in the chain of the fourth. None of those things are the same. So this carbon is asymmetric. Next down the chain. This guy has hydrogen is one. The carbon with a methane and hydroxide is to the amino group is three and the car boxes group is four. All different things. So that is also a symmetric. Finally, let's look at this last carbon in the chain. It's part of a car boxing group, but two of its bonds are part of that double bond to an oxygen. So it is not a symmetric. So we can just eliminate that one. So now let's head on over to our groups and see which one is not attached to an asymmetric carbon. Choice A says methyl group. But here's our methyl group right here attached to one of our asymmetric carbon. So choice A can be eliminated. B is hydroxyl group. There's a paradox a group attached to this first asymmetric carbon. We can eliminate B. See amino group amino group is here attached to the second asymmetric carbon C. Is eliminated. Now D. Is a phosphate group. We can remember that a phosphate group has phosphorus in it, and we don't have a phosphate group anywhere on this molecule, so Choice D. By elimination. And we can look over here is the correct answer. It is not attached to an asymmetric carbon. See you in the next video.

Which of the molecules shown in question 5 has an asymmetric carbon? Which carbon is asymmetric?

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Key Concepts

Asymmetric Carbon

Chirality

Stereochemistry