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When a given set of reactants undergoes multiple reactions in a given condition, then the products formed are called stereoisomers. One of these formed products is in a larger quantity than the others, and the entire reaction is called stereoselective reaction. Hence, we can say that, in stereoselectivity, one product is formed selectively more than the others.
Stereoselectivity
Stereoselectivity is a feature of an interaction that enables the formation of several products or stereoisomers. Stereoisomers have similar molecular formulas but different three-dimensional configurations.
Types of Stereoselectivity
Diastereoselective reactions are those in which a stereogenic centre is incorporated into a compound such that it forms diastereoisomers in uneven proportions.
Enantioselective reactions yield uneven quantities of the two enantiomers of such a chiral molecular product. Enantioselective reactions have enantiotopic and enantiofacial selectivity. It is described as the main or exclusively produced from one of the two enantiomers. Chiral substrates, reagents, catalysis, or solvents can be used to do this. Enantioselective reactions include a chemical attacking one of its two enantiotopic groupings or faces preferentially.
Stereoselective Reactions
Stereoselective reactions produce primarily one stereoisomer (or combination of enantiomers) of various diastereomers. Three compounds are produced by the eliminating reactions of 2-iodobutane with the existence of a base. Trans-2-butene, cis-2-butene, and 1-butene are also the three types of butenes. A stereoselective reaction is one in which a stereoisomeric product is produced due to the reactivity route being so much more favourable than all the others. Trans-2-butene is the main product, so we may say the process is synthesised.
The Principle of Stereoselectivity
According to the principle of stereoselectivity, a substrate should have pro stereogenic components that would be determined by the symmetry or, more specifically, the topicality of such a reactive group or faces. The approach to such a synthesis must be determined on a case-by-case basis, with no predetermined guidelines.
In a kinetic model governed by stereoselectivity, the mechanism of stereoselectivity will be the same if it’s diastereoselectivity or enantioselectivity. Two diastereomeric transitions are required to create the two stereoisomers. Stereoselectivity is proportional to the difference in limitless energy between them. A difference of 10 kJ mol-1 at room temperature causes the desired isomer to form in approximately 98 per cent of all cases.
The creation of distinct diastereomeric molecules results in stereoselectivity. The compound would’ve been racemic within thermodynamically controlled conditions. The stereoelectronic component, the steric aspect, as well as other electronic impacts should all be taken into account.
Stereoselective vs stereospecific reactions
Chemical reactions comprising organic molecules that produce products with various atomic configurations are referred to as stereospecific and stereoselective reactions. The key major difference between the two kinds of reactions would be that the reactant’s stereochemistry dictates the stereochemistry of the result in a stereospecific reaction.
The below table outlines the differences between stereoselective vs stereospecific
Stereoselective reactions | Stereospecific reactions |
A stereoselective reaction is the one in which the resultant stereoisomer is generated because the reaction path chosen is much more favourable than all the others. | A stereospecific reaction takes place when the stereochemistry of such reactants totally dictates the stereochemistry of either the result. |
Multiple products may emerge from a stereoselective reaction. | From a particular reactant, a stereospecific reaction generates a specific item. |
Differential steric impacts (the existence of bulky compounds induces steric hindrance) and electronics influences determine the reaction pathway’s selectivity. | The stereochemistry of such reactants influences the finished result of a stereospecific reaction. |
Conclusion
We studied stereoselectivity throughout this module, which is the property of chemically dissimilar compounds reacting in various ways to produce different products. We also looked at diastereoselection in acyclic systems with C-C and C=C bonds, as well as cyclic molecules, focusing on substituent location. Stereoselective reactions produce primarily one stereoisomer (or a pairing of enantiomers) from a set of diastereomers. Nucleophilic additions to cyclohexanones as well as other appropriate substrates have been used to demonstrate it.
