One of the following molecules (a)-(d) is D-erythrose 4-phosphate, an intermediate in the Calvin

One of the following molecules (a)-(d) is D-erythrose...

Key Concepts

Carbohydrate Phosphate Intermediates and the Calvin Cycle

In the context of photosynthesis, the Calvin cycle incorporates carbon dioxide into organic compounds that eventually lead to carbohydrate formation. Carbohydrate phosphate intermediates, such as the one described in the question, participate in these biochemical pathways, and their specific stereochemistry is critical for the precise interactions required in enzyme-mediated reactions.

Diastereomers

Diastereomers are stereoisomers that are not mirror images of each other. Unlike enantiomers, diastereomers have different physical and chemical properties, which often makes them easier to separate and analyze. In molecules with two or more chiral centers, changing the configuration at one (or some but not all) center(s) results in diastereomers.

Chirality Centers

These are atoms, typically carbons, that are bonded to four different substituents, causing the molecule to be non-superimposable on its mirror image. The presence of one or more chiral centers in a molecule introduces the possibility of having stereoisomers, which are compounds with the same molecular formula and connectivity but different spatial arrangements of atoms.

R/S Configuration

This is the system used to designate the absolute configuration of chiral centers. The R (rectus) and S (sinister) labels indicate the spatial arrangement of the substituents around the chiral center, determined according to the Cahn–Ingold–Prelog priority rules. An assignment of R configuration to a chiral center means that the substituents decrease in priority in a clockwise arrangement when viewed from a specific angle.

Enantiomers

Enantiomers are pairs of stereoisomers that are non-superimposable mirror images of each other. They have identical physical and chemical properties in an achiral environment but can interact very differently with other chiral molecules, such as biological receptors. This concept is crucial when assessing molecules that differ only in the absolute configuration at all chiral centers.

Transcript

00:01 So they tell us that dethyrosphosphate has both of its chirocerners with the r configuration.

00:09 And they want us to determine which one of these structures has that configuration.

00:14 Then they want us to determine if the following three molecules are going to be inantomers or diasteremers.

00:25 So let's go ahead and first figure out what a is.

00:28 And then we can get everything else based off of this.

00:34 So let's first start with this chiral center here.

00:41 So remember for the fisher projections, if it's on the backbone like this, they're assumed to be facing down.

00:50 So let's see.

00:53 So let's draw the little bow tie off on the side here to start.

00:58 Well, we know hydrogen should have the lowest priority.

01:03 So because of that, that's just going to be four, and that oxygen has the higher priority when we compare it with those two carbons because it has the highest atomic number.

01:15 Now comparing these two carbons here, well, let's see.

01:18 So this carbon is attached to essentially two oxygens.

01:22 The carbon below is only attached to one oxygen.

01:27 And since oxygen has a higher atomic number than the carbon, that would mean having two oxygens is going to be better.

01:34 So there's going to be two going up and three going down.

01:39 So we want to make it so our four is in the back.

01:45 So what i'm going to do is i'm going to pinch one here and then rotate these other ones.

01:51 So i'm going to move four to two, two to three, and then three to four.

01:55 And doing that.

01:58 So we didn't move one.

02:02 Now three got moved to four, four got moved to two, and then two got moved to three.

02:09 So if we were to look at the orientation of this now, so we go one, two, three, like that, and notice we rotate to the right, so that means it's going to be r.

02:23 So the way i like to remember is when you normally draw an r, when you go to do the little loop, notice how you rotate to the right to do it.

02:31 So it's going to be to the right, so that means this first one is going to have a chirality of r.

02:38 And now when we go to do this second one here so let's draw the little bowtie once again so again hydrogen is going to have the lowest priority that oxygen from the alcohol is going to have the higher priority now we need to decide well what has the higher priority going up or going down well let's draw this actually out so we can maybe see a little bit better so this has two hydrogens attached and then attached to this oxygen like that so when we come down to this carbon versus this carbon, notice that this carbon on the bottom has one oxygen and two hydrogens.

03:29 Coming up, we have one oxygen, one hydrogen, and a carbon.

03:34 So if we were to kind of do like a little punchout game, notice this oxygen knocks that oxygen out, this hydrogen knocks this hydrogen out, and then we have to compare the hydrogen to that carbon...

Please give Ace some feedback