Asymmetric Induction: Definition, Factors & Methods

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, we will learn about asymmetric induction, its definition, what conditions allow it to occur, and what types of reactions use asymmetric induction. Updated: 05/16/2022

What is Asymmetric Induction?

When chemical compounds react with each other, specific atoms on the molecule will participate in the reaction. But chemical compounds aren't just 2D objects like we see on paper. Each of those atoms exist in a 3D plane. The atom could be sticking out, while another atom that plays a role in the reaction may be pointing backward. When two compounds have the same 2D structure but different 3D structures that are mirror images of each other, they are called enantiomers.

So, when a reaction occurs, sometimes only one of the enantiomers is formed. When one enantiomer is formed preferentially over another enantiomer, this is called asymmetric induction.

The two enantiomers that form are referred to as the D form and the L form based on what direction it rotates plane-polarized light. Most reactions will create both enantiomers, creating a racemic mixture. This means that the D and L forms are both formed in equal proportions (the mixture consists of 50% of each form). When this is the case, the mixture doesn't rotate any plane-polarized light because the two directions cancel each other out. When one is formed more than the other, the mixture will start to rotate light in that direction.

The amino acid alanine can form enantiomers D and L. L alanine is the only one that occurs naturally, because biological systems asymmetrically induce only one enantiomer.
D and L alanine

Factors Affecting Asymmetric Induction

In order for asymmetric induction to occur, the product needs to be chiral, or in other words, it needs to have enantiomers of each other. Next, the reaction needs to preferentially produce one enantiomer over the other.

When two enantiomers are possible to form in a reaction, asymmetric induction occurs based on the following factors:

  • How close the two chiral centers are to each other

Different bonds have different lengths. If the bond involved in the enantiomer (the two chiral centers) is a very short bond, then asymmetric induction will be more likely to occur. The longer the bond is, the less likely that asymmetric induction will occur.

  • How much electronic control exists

If all of the groups attached to the chiral centers have similar electronic control (for example similar electronegativity) then asymmetric induction is less likely to occur.

  • Whether there is an intermediate product with two possible diastereomers

A diastereomer is like an enantiomer, except the two are not mirror images of each other. If one diastereomer can form much easier (for example, if it is easier to access the backside because a large molecule blocks the front side) and requires less energy to form, then that diastereomer will be more likely to form. This limits the types of intermediate products that can form, thus limiting what the final products can be as well. There needs to be a diastereomer intermediate product for a reaction to have asymmetric induction. The bigger the energy difference between the two diastereomers, the more likely asymmetric induction will occur.

Methods of Asymmetric Induction

There are several different reactions and methods for asymmetric induction to occur. These include:

  • Sharpless epoxidation, which takes alkenes and oxidizes them into epoxides.
  • Amino acid synthesis, in which only the L configuration of amino acids naturally exist (for most amino acids). Some synthetic reactions come close to only producing the L configuration, but biological systems are much more efficient at it.
  • Reduction of ketones using a chiral reducing agent, in which a ketone is reduced to an alcohol, and depending on the chirality of the reducing agent, will produce a specific enantiomer.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it now
Create an account to start this course today
Used by over 30 million students worldwide
Create an account