Enantiomers are the chiral molecules that are mirror images of one another and are not superimposable. Diastereomers are the stereomer compounds with molecules that are not mirrored images of one another and that are not superimposable. They are non-superimposable mirror images of each other. This means that they are mirror images of each other, but you can't stack them on top of each other and have them line up exactly the same.
Enantiomers and diastereomers are types of stereoisomers. In this lesson, we'll learn what the difference is between these types of stereoisomers and how to differentiate between them. There are two types of Isomers, stereoisomers, and structural isomers.
Structural isomers have the same molecular formula but are different in their bond connection and order. On the other hand, Stereoisomers, differ in the spatial arrangement of their structures. Again the stereoisomers are divided into Enantiomers and Diastereomers. What are Enantiomers and Diastereomers? A chiral molecule has an image that is not the same as its mirror image and, it is typically characterized by a carbon centre with 4 different atoms bonded to it.
These atoms must be chemically distinguishable for a molecule to be qualified as a chiral and thus an Enantiomer. The tetrahedral carbon to which the different atoms are attached to is called the stereocenter. See the difference below, the two molecules have the same formula and the structuring of the atoms so to identify them we have to label one the S and the other R, depending on the clockwise configuration of the atoms from the lowest atomic mass to highest atomic mass.
Diastereomers are the stereomer compounds with molecules that are not mirror images of one another and that are not superimposable. The perfect example of diastereomers is when you look at the cis and trans isomer structure. See the cisbutene and the transbutene structures below:. See the compounds are identical but the arrangements are different, and they are not the mirror images of each other.
Ernest Z. Explanation: Enantiomers Enantiomers are chiral molecules that are nonsuperimposable mirror images of each other. For example, D-glucose and L-glucose are enantiomers.
Chiral molecules A chiral molecule is a molecule that is not superimposable on its mirror image. For example, here are two chiral molecules. They are chiral, but they are not enantiomers. Related questions Question a.
Why are organic compounds important? We will start with a common four-carbon sugar called D-erythrose. A note on sugar nomenclature: biochemists use a special system to refer to the stereochemistry of sugar molecules, employing names of historical origin in addition to the designators ' D ' and ' L '.
You will learn about this system if you take a biochemistry class. As you can see, D -erythrose is a chiral molecule: C 2 and C 3 are stereocenters, both of which have the R configuration. In addition, you should make a model to convince yourself that it is impossible to find a plane of symmetry through the molecule, regardless of the conformation.
Does D-erythrose have an enantiomer? Of course it does — if it is a chiral molecule, it must. The enantiomer of erythrose is its mirror image, and is named L-erythrose once again, you should use models to convince yourself that these mirror images of erythrose are not superimposable. Notice that both chiral centers in L-erythrose both have the S configuration. In a pair of enantiomers, all of the chiral centers are of the opposite configuration.
What happens if we draw a stereoisomer of erythrose in which the configuration is S at C 2 and R at C 3? This stereoisomer, which is a sugar called D-threose, is not a mirror image of erythrose. D-threose is a diastereomer of both D-erythrose and L-erythrose. The definition of diastereomers is simple: if two molecules are stereoisomers same molecular formula, same connectivity, different arrangement of atoms in space but are not enantiomers, then they are diastereomers by default.
In practical terms, this means that at least one - but not all - of the chiral centers are opposite in a pair of diastereomers.
By definition, two molecules that are diastereomers are not mirror images of each other. L-threose, the enantiomer of D-threose, has the R configuration at C 2 and the S configuration at C 3. L-threose is a diastereomer of both erythrose enantiomers. In general, a structure with n stereocenters will have 2 n different stereoisomers.
We are not considering, for the time being, the stereochemistry of double bonds — that will come later. For example, let's consider the glucose molecule in its open-chain form recall that many sugar molecules can exist in either an open-chain or a cyclic form. There are two enantiomers of glucose, called D-glucose and L-glucose. The D-enantiomer is the common sugar that our bodies use for energy. In L-glucose, all of the stereocenters are inverted relative to D -glucose.
That leaves 14 diastereomers of D-glucose: these are molecules in which at least one, but not all, of the stereocenters are inverted relative to D-glucose. One of these 14 diastereomers, a sugar called D -galactose, is shown above: in D-galactose, one of four stereocenters is inverted relative to D-glucose. Diastereomers which differ in only one stereocenter out of two or more are called epimers. D-glucose and D-galactose can therefore be refered to as epimers as well as diastereomers.
We know that enantiomers have identical physical properties and equal but opposite degrees of specific rotation. In addition, the specific rotations of diastereomers are unrelated — they could be the same sign or opposite signs, and similar in magnitude or very dissimilar.
Constitutational isomers or structural isomers are molecules with the same chemical formula but different structures of atoms and bonds.
For example, both 3-methylpentane and hexane have the same chemical formula, C 6 H 14 , yet they clearly have different structures:. Another example involves functional groups. Methoxy methane, an ether, and ethanol, an alcohol, both have the chemical formula C 2 H 6 O:. Identify the following as either a constitutional isomer or stereoisomer.
If stereoisomer, determine if it is an enantiomer or diastereomer.
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