What are the reasons for the differences in physicochemical properties between epimers?

A pair of diastereomers produced by the change in the configuration of a single atom mentioned in the title is called epimer. Enantiomers are achiral.

The physical and chemical properties in the environment are consistent; However, this does not mean that only carbon-differentiated epimers should maintain close physicochemical properties in achiral environments (omitted below). In other words, epimers can have very different physicochemical properties. Here are a few examples:

1.Separation of enantiomers by salt formation For a pair of acidic (basic) chiral isomers, it can be resolved using a chiral base (acid). If this chiral base (acid) has only one chiral carbon, it can be seen as forming a pair of epimeric salts.

their solubility.

Properties such as melting point can vary greatly, thus splitting a pair of isomers. There are many reasons for the differences in the physicochemical properties of hydrogen bonds in the epimers, but in general it is because the change in configuration causes certain interactions in a pair of molecules to change. For example, the figure below shows the difference in physicochemical properties caused by hydrogen bond interactions

Hence the intermolecular forces in the trans structure.

Stronger and with a higher melting point. Differences in this interaction can also be reflected in magnetic anisotropy NMR spectra in epimers. For chiral alcohols, amines, and other compounds, one way to determine the absolute configuration is to combine it with mosher'S acid forms ester amide compounds.

s)-mosher'The structure of s acid is as follows: <>

The dominant conformation for the formation of ester compounds is shown in the figure below, where hydrogen and carbonyl groups are formed.

Oxygen parallel, high electronegativity.

The cf is away from the carbonyl key shaft. In this case, the diamagnetic circulation of the phenyl group in NMR shields the X group on the same side; The electronic effect of the methoxy group deshields the ipsilateral y-group: <>

This results in the use of (r)(s)-mosher'The chemical shifts of hydrogen in X and Y are reversed during esterification of S acid, from which the absolute configuration of the compound can be identified. In addition, many factors, such as the distortion of the molecular carbon chain in the epimer, can also cause differences in interactions. In short, it is a common phenomenon that the physicochemical properties of epimers are quite different.

In fact, it is relatively common for diastereomers to have very different properties, and there are many asymmetric syntheses that synthesize enantiomer separation first and then chiral conversion. As for the mechanism, I don't know very well. One possible reason is that the groups on the chiral carbon have hydrogen bonds, large steric hindrance, etc., so that the molecule can only be coiled in a certain way, so that the hydrogen bond is exposed to the body acceptor or forms an intramolecular hydrogen bond, so the physical properties will be changed a lot.

Similar proteins cannot be curled if they have chiral errors, and they are inactive. But one is soluble and the other is insoluble. Ordinary molecules will enter the solution.

When studying organic chemistry, two things that are often considered are electron effects and spatial effects. The physicochemical properties between epimers depend more on spatial effects, and the steric hindrance effect is one, especially in chiral environments such as organisms, the difference will be obvious. <>

In organic matter, the difference between epimers is usually located in a single asymmetric carbon atom, and in general, this carbon is labeled, such as D-glucose, the C2 isomer, D-mannose. If not indicated, C2 is usually assumed, e.g., the epimer of D-glucose is D-mannose. Epimers (English:

epimer) refers to a pair of diastereomers with a different configuration of only one asymmetrical atom in a molecule containing two or more tetrahedral chiral centers. The associated isomerism is called epimerism. If the chiral atoms with different configurations are at the end of the chain, then these two isomers are also called"End-based epimer"。

In other cases, they can be used separately"CN epimer"Indicate that n is the position number of the asymmetrical atom, and c can also be the atom of other tetrahedral configurations. <>

In stereochemistry, among the stereoisomers containing multiple chiral carbon atoms, only one chiral carbon atom has a different configuration, and the rest of the diastereomers with the same configuration are called episomers.

The difference in the performance of the object is mainly reflected in the optical rotation. That is, when polarized light passes through the material, a set of enantiomers causes the polarized light to rotate in different directions, but with the same optical rotation ability.

The chemical properties are almost similar. The difference can only occur when two enantiomers with steric hindrance are reacted. As a result, most of the synthesized molecules are almost half left-handed and right-handed.

The differences in chemical properties are mainly reflected in biochemistry. A large number of proteins and other molecules have a preferential form of optical isomerism. If there is a biological macromolecule with opposite optical rotation, it may not participate in the biochemical reaction due to structural mismatch.

Therefore, in the pharmaceutical and other fields, it is important to choose the right enantiomer.

The position of the hydroxyl group at position C2 is different, and the position of other groups remains unchanged, which is a case of epimerism.

Epimers are stereoisomers containing multiple chiral centers, only one chiral center has a different configuration, and the rest are diastereomers with the same configuration.

Isomers mainly include carbon-dry isomerism, functional group type isomerism, functional group position isomerism, and most isomers are tectonic isomers.

Epimerism refers to the presence of a plurality of chiral carbon atoms, one of which is of the opposite configuration, and the other chiral carbon atoms have the same configuration, so that the two isomers are called epimers of each other, and the composition and structural formula of the two epimers are the same, and they are not structural isomers, but configuration isomers in stereoisomerism.

L-isoleucine with two chiral carbon atoms is partially converted into its diastereomer, D-allisoleucine, only on the -carbon atom.

Containing multiple chiral carbon atoms, one of the chiral carbon atoms has the opposite configuration, and the other chiral carbon atoms have the same configuration, so the two isomers are called epimers. The composition and structural formula of the two epimers are the same, and they are not tectonic isomers between them, but conformational isomers in stereoisomerism.

The molecules of the epimer have only one chiral carbon atom with opposite configurations, so they are not enantiomers, but diastereomers. Two optical isomers that contain only one chiral carbon atom, such as D-glyceraldehyde and L-glyceraldehyde, are not called epimers with each other, although the configuration of the chiral carbon atoms is opposite, they are enantiomers of each other.

Under certain conditions, the process of changing from one epimer to another is called epimerization. In the event of epimerization, the optical rotation will inevitably change, and even the direction of the optical rotation may also change. The transition between two optical isomers containing only one chiral carbon atom is not called episomralization, and is generally referred to as racemization, or racemization.