Stereochemistry is a branch of chemistry. The stereochemistry of organic compounds is a very interesting subject for chemistry readers. The word stereo meaning three-dimensionality that means Stereochemistry is three-dimensional chemistry. In simple words, Stereochemistry is the study concerning the three-dimensional arrangement of the atoms in space of the molecule i.e. three-dimensional structure of the molecule. As the organic branch of chemistry is the largest branch of chemistry with a huge number of compounds. Therefore, a vast amount of Stereochemistry can be found among the organic compounds.
Isomers of Organic Compound
To learn the Stereochemistry of Organic compounds we must have an idea about the isomers of the organic compound.
Compounds with the same molecular formula but with a different chemical structure or same chemical formula but have different physical and chemical properties even react differently with plane-polarized light are known as the Isomers of each other. The isomers are mainly two types in organic chemistry. They are-
- Constitutional isomers, and
The isomers generate only for different arrangements of the atoms in the molecules are known as the constitutional isomers. There are a different number of classes of constitutional isomers. Such as-
- Chain or nuclear isomers,
- Functional group isomers,
- Positional isomers,
- Metamerism, etc.
This type of isomerism is not our concern for this article. If you want an informative article on those isomers please write a comment below.
Stereochemistry of Organic Compound
In this particular article, we will try to make u understand the stereoisomers because Stereochemistry focuses on the stereoisomers in chemistry
To learn the stereoisomer we should know what is configuration in chemistry. The arrangement of atoms and groups in a molecule in the three-dimensional space is known as the configuration. For the difference of the configuration in a molecule, the stereoisomers take place.
In simple words, isomers differ in the way the atoms are oriented in space, but not in which atoms are bonded to which atoms are called Stereoisomers.
Cis-2-butene and trans-2-butene are examples of the stereoisomers. Here, the cis and trans isomer have the same chemical formula and atomic arrangement. But the orientation of the atoms and group in space is different.
Conditions to be optical isomers
To be optical isomers a compound must achieve some properties. These properties are the conditions for a compound to be either optically active or not. The conditions are given below-
- To be an optical isomer a compound must be optically active,
- In an organic compound if a chiral carbon is present the compound becomes asymmetrical and becomes optically active,
- The optically active isomers must rotate the plane-polarized light in different directions.
- For the chiral center, two different superimposable configurations of an optically active compound become optical isomers.
The optically active compounds or optical isomer rotate the plane-polarized light in opposite direction but in the same numeric angle are called the enantiomer or enantiomorph of antimer or anti-pod. For example, l-lactic acid and d-lactic acid are enantiomers of each other.
When two optically active compounds containing a chiral center are noted as superimposable and they rotate the plane-polarized light in different rotation angles, then they are called diastereomers.
For example, 3-chlorobutanol-2 has enantiomers as well as diastereomers. Here are two chiral centers. Therefore, 22 = 4 isomers are possible.
Polarimeter – an instrument used to measure the optical activity of a substance is known as the Polarimeter.
Dextrorotatory – when the plane of polarized light is rotated in a clockwise direction when viewed through a polarimeter is known as the Dextrorotatory.
It is denoted by (+) or (d) ∗∗∗ do not confuse with D
levorotatory – when the plane of polarized light is rotated in a counter-clockwise direction when viewed through a polarimeter.
It is denoted by (-) or (l) ∗∗∗ do not confuse with L
The angle of rotation of plane-polarized light by an optically active substance is proportional to the number of atoms of the substance in the path of the light.
Specific rotation – The angle of rotation of the plane-polarized light with a sample of 1.00 grams per cm-3 in a 1 tube. the specific rotation is measured by the following equation
where, α = observed rotation (D = sodium lamp, λ = 589 nm).
[α]D =l x d
where, l = length (dm), d = concentration (g/cc)
(+)-alanine [α]D = +8.5
(-)-lactic acid [α]D = -3.8
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