Xylose is a common sugar found in many types of wood, including maple and cherry. Because it is

Xylose is a common sugar found in many types of wood,...

Key Concepts

Chirality Centers

Chirality centers are atoms, typically carbon, that are bonded to four different substituents, leading to non-superimposable mirror images known as enantiomers. Their presence is fundamental in stereochemistry, giving rise to molecules with distinct spatial arrangements and often different chemical and biological properties.

Cahn-Ingold-Prelog (CIP) Priority Rules

The CIP priority rules provide a systematic method to assign priorities to the substituents attached to a chiral center based on atomic numbers and connectivity. These rules are essential for determining the relative arrangement of groups, which is a prerequisite for assigning absolute configurations such as R and S.

R/S Configuration Designation

The R and S configuration notation is used to denote the absolute configuration at a chiral center. Once priorities are assigned using the CIP rules, the molecule is oriented so that the lowest priority group is positioned away from the observer, and the order of the remaining substituents is analyzed to determine a clockwise (R) or counterclockwise (S) arrangement.

Fischer Projections

Fischer projections are a graphical representation used primarily for depicting the stereochemistry of sugars and other molecules with multiple chiral centers. They simplify the visualization of three-dimensional structures on a two-dimensional plane, making it easier to assess the configuration of each chiral center.

Transcript

00:01 So here we have the plus and antimir of xylos, and we want to go ahead and identify all of its chiral centers, as well as assigned configuration for each of those chiral centers.

00:13 So looking from left to right, we see that our first carbon is our aldehyde.

00:18 That is not going to be a chiral center because it is not connected to four different groups.

00:22 And then so our next carbon here, which would be the one denoted in red, this actually is going to be a chiro center because it is connected to the aldehyde group, an alcohol group, a hydrogen group, and then the rest of the connecting chain.

00:39 And so what we can do is we can assign configuration for this.

00:43 And so, of course, our oxygen, which is part of our alcohol group, is going to be number one, and then the aldehyde is going to be number two, and then the rest of the connecting chain here it's going to be number three, and our hydrogen is number four.

01:02 And so what we see is what appears to be going counterclockwise.

01:07 And so we would say that's s, however, we want the hydrogen to be going away from us.

01:11 And so we would invert that configuration.

01:14 And instead of s, we are actually going to get r for this.

01:19 Okay.

01:20 And now looking at the next carbon here, this will actually be another chiral center because we have our left side of the chain, which is connected to the aldehyde.

01:33 We have the right side of the chain, which is connected to an ethanol at the terminal positions.

01:38 And then we are also connected to a alcohol and a hydrogen.

01:43 So these are four different groups.

01:44 And so we would say this is cairo, and we should be able to sign a configuration.

01:48 And so just like before, our alcohol is going to be number one because the oxygen has the highest priority.

01:53 And then going from now we have the two carbons on the left and the right, and those are connected to the same groups except at the terminal position, right? so we have our ethanol versus our aldehyde, and our aldehyde is going to take the priority over the ethanol because that carbon is directly bounded to the oxygen twice because of the double bond, whereas in ethanol it is only bound once, or is it only single bonded.

02:23 And so the left side of the chain is going to be prior to number two.

02:28 Right side of the chain is number three.

02:31 And our hydrogen is number four.

02:34 So it looks like we're going clockwise...

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