Hi everyone. Today in this video let us discuss about the enomers. Let us take the structure of one of the carbohydrate and this is a well-known carbohydrate is the D-glucose.
Let us give the numbering to this D-glucose. We have to start the numbering from the aldehyde. So this is one two three four five six. So this is a six carbon carbohydrate that is a D-glucose.
Now let us take another structure. What is this structure? This is nothing but the D-mannose. Now if we compare the D-glucose and D-mannose, there hang similar stereochemistry at few of the carbons but a different stereochemistry at the one of the carbon.
So here you can observe at the second carbon the OH group is on the right side in the D-glucose but here in the D-mannose it is on the left side. But the orientation of the groups at the other carbons is identical in D-glucose and D-mannose so these two compounds are going to differ in their configuration at second carbon only. That's why these carbohydrates are called as epimers.
and since they are going to differ at the second position they are called as C2 epimeres. Similarly we can take another structure this is the D-galactose and again if you observe the D-glucose and D-galactose they are going to differ in the configuration at the fourth carbon. Here the OH group is on the right side in the D-glucose and left side in the D-galactose.
So again the D-glucose and D-galactose are the epimeres they are the C4 epimeres. In this way when two carbohydrates are going to differ In configuration only at one carbon they are called as epimers and these two compounds are not same. So epimers exist as different compounds. Then what about the enomers?
There is a relation between the enomers and epimers. Now let us see what are the enomers. Again let us take the structure of the D-glucose and let us give the numbering. Now this D-glucose is in aldose and since it is having a carbonyl functional group at the aldehyde. This can undergo the nucleophilic attack and it can form a nucleophilic addition reaction.
When this D-glucose is going to be dissolved in the water, it undergoes the nucleophilic attack within the structure such that this aldehyde function group is going to be reacting with the OH group of the fifth position. Now because of this reaction, this D-glucose undergoes the nucleophilic addition such that it is going to form a cyclic structure like this. Now let us give the numbering to the cyclic structure.
This is one, two, three, four, five, six, seven, eight, nine, three four five and six and again here it is like the six carbons but in the open chain D-glucose the first carbon is an aldehyde but here in the cyclic form it is going to alcohol by nucleophilic addition. So during the conversion of the aldehyde into alcohol the OH group is going to form which may be oriented in any way at the first carbon. So here we have shown that OH group is present on the left side but it may also be present on the right side. In this way on cyclization of the D-glucose it will give the two products. So this is the D-glucose.
Now when it is undergoing the cyclization it can give one of the product like this. Otherwise it can give the another product like this. You can see that both of these compounds are going to differ by their configuration at first carbon.
And here in this structure the OH group is on the left side. It is called as beta D-glucose. And when this OH group is on the right side it is called as alpha D-glucose. And here we have to consider the configuration at the enomeric carbon that means in this D-glucose at the first carbon. Now we can also represent the alpha D-glucose and beta D-glucose by using the Havertz projection.
So this is the Havertz projection and here you can observe that it is forming a six-membered cyclic ring system with auxin. So these cyclic forms are called as pyranoges because the pyrone is having a six-membered ring system with auxin. Now the carbohydrates which are having the pyrone ring system are called as pyranoses and here you can observe the OH group at the first carbon is attached such that it is below the plane.
Now such type of configuration we call alpha D glucose. So according to the habit projection alpha configuration indicates the group is below the plane. Similarly, this is the beta D glucose.
Here you can observe the OH group is attached above the plane. So this is the beta D glucose. So according to the Havertz projection, the beta configuration means the group is attached above the plane. In this way, we can represent the alpha D glucose and beta D glucose by using the Havertz projection. So when this open chain glucose is going to be dissolved in the water, the aldehyde will undergo the nucleophilic attack such that it is going to form the both alpha D glucose as well as beta D glucose.
but they are not formed at the equal amounts and the relative amounts of these alpha d glucose and beta d glucose depends on their stability when the open chain glucose is going to be dissolved in the water the alpha d glucose going to be formed from zero percent to the 36 percent. Similarly the beta D glucose which is 0 percent in the open chain form is now converted into 64 percent in the aqueous solution. So within the aqueous solution 36 percent of alpha D glucose and 64 percent of beta D glucose will be present with very very little amount of the open chain form. In this way glucose mainly exists as a cyclic form in aqueous solutions.
And here we can clearly observe that The beta-D-glucose is more formed compared with the alpha-D-glucose. That means which is more stable? Higher the stability, higher the rate of formation. So here simply it indicates that beta-D-glucose is highly stable that's why it is formed by 64 percent and alpha-D-glucose is somewhat less stable compared with the beta form so it is formed up to 36 percent. Now you can observe this alpha D glucose and beta D glucose.
Both are having the similar configuration at all carbons except the first carbon. So at the first carbon alpha D glucose and the OH group below the plane but in the beta D glucose it is above the plane. So now these are the cyclic carbohydrates which are going to differentiate their configuration at only one carbon.
They are called as enomers. So, enomers are simply cyclic epimers. These enomers are going to differ by their configuration at one carbon particularly at the first carbon and that carbon is called as enomeric carbon.
Then what is enomeric effect? Enomeric effect is the difference in the chemical properties of formed cyclic enomers. We have seen that whenever the open chain D-glucose is going to be dissolved in the water it produces alpha D-glucose and beta D-glucose.
but the beta-D-glucose is more formed compared with the alpha-D-glucose because of higher stability. So this difference in their stability as well as the chemical properties because of their difference in configuration at only one carbon is called as enumeric effect. So now we can observe the differences between the alpha-D-glucose and beta-D-glucose. The first one is the stability.
All we have seen which enomer is more stable. So here the beta D-glycos is more stable than the alpha D-glycos. So that's why beta D-glycos is more formed in the aqueous solutions. Then what about the reactivity? The reactivity of the cyclic enomers depends on the opening of the cyclic ring.
Since the beta D-glycos is more stable, it is not easily opened. So the reactivity will be reversed compared to the stability. alpha D glucose will have more reactivity compared with the beta D glucose. Similarly, we can observe a difference in the optical rotation.
The alpha D glucose, because of the higher reactivity, it is having more optical rotation compared with the beta D glucose. So here stability is more for beta D glucose and reactivity is more for alpha D glucose. And this optical rotation is also different between the alpha and beta D glucoses, which results in a phenomena called mutarotation.
So what is mutarotation? Mutarotation is a change in the optical rotation with respect to time. For example, if you take the alpha D glucose, the alpha D glucose is having the OH group below the plane and this alpha D glucose is having a optical rotation of plus 112.2 degrees.
Pure alpha D glucose will have an optical rotation of 112.2 degrees. But when it is dissolved in water, what happens? When it is dissolved in the water, the optical rotation is going to slowly change such that it is going to reach to a value plus 52.7 degrees.
So this phenomenon what we call mutarotation. Similarly, when we take the beta-D-glucose, the beta-D-glucose is having a OH group above the plane. Now this beta-D-glucose in the pure form, it is having an optical rotation of plus 18.7 degrees. But when it is dissolved in the water, again the optical rotation is slowly increases.
Optical rotation. to 52.7 degrees. In this way both alpha d glucose and beta d glucose change the optical activity and they will reach a particular value that is a 52.7 degrees. So this phenomenon what we call mutarotation. Why it is like this?
This is simply because of the relative stability of alpha d glucose and beta d glucose. When pure alpha d glucose is going to be dissolved in the water It is somewhat converted into beta-D-glucose such that within the solution 36% is alpha-D-glucose and 64% is beta-D-glucose. That's why optical rotation is going to decrease to the 52.7 because the beta-D-glucose will have less optical rotation compared to the alpha-D-glucose. Similarly, when we take the pure form of the beta-D-glucose which will have a less optical rotation like plus 18.7 degrees.
But within the solution, the beta-D-glucose is somewhat changed to the alpha-D-glucose such that it is going to form the 36% alpha-D-glucose and 64% beta-D-glucose. And since this beta-D-glucose is converted to alpha-D-glucose, the optical rotation is going to slowly increases up to the 52.7 degrees. In this way, these enumers can show the mutarotation that is a change in the optical rotation with respect to time when they are dissolved in the water.
This change in the optical rotation is because of the enomeric effect due to the difference in their stability of the enomers. So that's about the enomers. Enomers are the simply cyclic carbohydrates which are going to differ in their configuration at one carbon particularly at the enomeric carbon. So enomers can be considered as cyclic epimers. So they are going to differ in their configuration at only one carbon in cyclic form.
And enomers will have the different chemical properties. they will have the different stability for example beta d glucose is more stable than the alpha d glucose and reactivity is more for alpha d glucose compared with the beta d glucose and they also show the mutar rotation changing the optical rotation with respect to time because of their difference in the relative stabilities so that's about the enumers hope you have enjoyed this video if you like this video please subscribe to our channel share this video with your friends post your comments in the comment box thank you for watching this video