Kagan and Soai: how one hand takes over
About this app
Enantiomeric excess ee made visible: Kagan's non-linear effect with catalyst pairs (sluggish mixed pairs lift the product above the line) and Soai's autocatalysis, in which the product copies itself and a small excess grows to over 90 % within a few rounds. Plus 37 runs without initial excess: 18 × R, 19 × S.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
What it is about
Many reactions give image and mirror image in a 50 to 50 ratio. How strongly one hand predominates is measured by the enantiomeric excess ee = (R − S)/(R + S). In 1986 Henri B. Kagan showed that a catalyst with two chiral ligands can give a product whose ee is higher than that of the ligand if mixed pairs are more sluggish (positive non-linear effect). In 1995 Kenso Soai found a molecule that catalyses its own formation: 5 percent excess became 90 percent within a few rounds. Both received the 2026 Nobel Prize in Chemistry for this.
What the app shows
In the Kagan scenario, 30 catalyst pairs of right and left ligands randomly form matching and mixed pairs. Bars show the shares in catalyst and product, and a chart compares the expectation as a straight line with the model curve. In the Soai scenario a flask fills round after round, the excess grows in the chart, and a dashed line shows the simple copy without amplification. 37 tubes show the experiment with no initial excess at all: the right hand won 18 times, the left hand 19 times.
Try it yourself
Drag the ee of the catalyst and see how far the product lies above the line. Let the mixed pairs work too, and the curve drops onto the line. For Soai you choose the initial excess, the 1995 molecule or the 2003 variant, and compare the rule "pairs" with the simple copy. Curve and rounds are models; the real measured values are in the info panel.
Frequently asked questions
- What is enantiomeric excess (ee)?
- The ee states how strongly one enantiomer predominates in a mixture: ee = (R − S)/(R + S). A 50 : 50 racemate has 0 percent, a pure enantiomer 100 percent, and a 60 : 40 mixture 20 percent.
- What is a non-linear effect in asymmetric catalysis?
- It was expected that the ee of the product is proportional to the ee of the chiral ligand. In 1986 Kagan showed that this does not hold when two ligands sit on the metal: if mixed pairs are more sluggish, the product lies above this line; if they are more reactive, below it.
- What happens in the Soai reaction?
- A pyrimidyl alkanol catalyses the addition of diisopropylzinc to a pyrimidine aldehyde, the reaction that forms the alkanol itself. Because it favours its own hand and slows the other, a small excess grows with every round. With no initial excess at all, chance decides which hand wins.
- What can I adjust in the app?
- For Kagan, the ee of the catalyst and whether mixed pairs work too. For Soai, the initial excess, the 1995 or 2003 molecule, the rule and the number of rounds, plus the 37 runs without initial excess.
Subject: Chemistry
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