Which of the other six D aldohexoses yield optically active aldaric acids on oxidation, and whic

Which of the other six D aldohexoses yield optically active...

Key Concepts

D-Aldohexoses

D-Aldohexoses are six-carbon sugars that contain an aldehyde group at one end. They have multiple stereogenic centers, and their spatial configuration defines different isomers. These molecules are fundamental in carbohydrate chemistry, and their properties, such as reactivity and optical activity, are determined by the arrangement of hydroxyl groups along the carbon chain.

Oxidation to Aldaric Acids

Oxidation of aldoses to form aldaric acids involves converting both the aldehyde and the primary alcohol group at the opposite terminal into carboxylic acids. This process is an important transformation in carbohydrate chemistry that changes the functionality and can affect the stereochemical properties and optical activity of the sugar derivative.

Optical Activity

Optical activity refers to the ability of a chiral compound to rotate the plane of polarized light. In the context of sugar oxidation, the optical activity of the aldaric acid product depends on whether the molecule possesses overall chirality or, alternatively, an internal plane of symmetry that could render it optically inactive despite having multiple chiral centers.

Meso Compounds

Meso compounds are molecules that contain multiple stereogenic centers but are overall achiral because of an internal plane of symmetry. This symmetry leads to cancellation of optical activity, so even though the individual centers are chiral, the molecule does not rotate plane-polarized light. In carbohydrate oxidation, some aldaric acids become meso compounds due to symmetric arrangements of substituents.

Stereochemistry of Carbohydrate Oxidation

The stereochemistry in carbohydrate oxidation is crucial because the spatial arrangement of the hydroxyl groups in the aldohexoses influences the configuration of the resulting aldaric acids. Depending on the relative positions of these groups, the oxidation process may either preserve chirality and yield an optically active product or create a symmetrical, meso structure that is optically inactive.

Transcript

00:01 All right, so for problem 20, we have this six aldohexosis that weren't mentioned in problem 19.

00:09 And so this problem is asking for us to turn all of this into their alderic acids, and we're going to figure out which one would be optically active and which one would not be optically active, or in other words, would be a meso compound.

00:26 Okay? so again, just to remind everyone, turning this into the alderic acid version just means take that aldehyde and turn it into cooh for carboxylic acid, and the same is true for that last carbon.

00:46 So carbon 1 and carbon 6 would be a carboxylic acid.

00:54 So let's go ahead and just erase all those extra oxygen and hydrogen.

01:01 Okay, so we're just turning all of it into c -o -o -h.

01:05 That's all we're doing.

01:13 So we're just erasing all that.

01:27 Okay, so almost done here.

01:37 All right, so now that we're done, let's go ahead and just replace all of those with c -o -o -h.

01:45 Okay, so i accidentally deleted that carbon in there.

01:53 Okay, so while we're doing that, we are looking for plane of symmetry okay because the minimum requirement of being optically active is to not have a plane of symmetry so if we do have one if we find one that means that structure would not be optically active okay so that's all we're going to be doing after this okay so starting with the altros okay, starting with d -alros, do we see a plane of symmetry? i don't think so.

02:32 Okay, so i'll just go ahead and just put an x right next to it, okay? to signify that we don't have a plane of symmetry.

02:39 Okay, so next, de -manos...

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