Nobel Prize in Chemistry 2026 · notebook page

Mirror chemistry: guess first, then seehow a reaction can pick one hand

The 2026 Nobel Prize in Chemistry went to Henri B. Kagan and Kenso Soai . Many molecules come in two mirror-image forms, like your left and right hands. This page shows you one pair, then asks three questions about them. Make a guess first, then reveal the answer. Some answers are real measurements; the rest come from small toy models, and each number says which it is.

Start here

Your hands are mirror images

Hold your hands palm to palm: they match. Now lay one on top of the other, both palms down: the thumbs point opposite ways. No turn makes them fit. Many molecules are like that. Below is one, alanine (a building block of proteins), and its mirror image. Drag to turn them.

Drag either molecule to turn both.

Structures: PubChem (NCBI), compounds , public domain. Letters on the balls: C carbon, N nitrogen, O oxygen; small balls are hydrogen.

Question 1 of 3 · Kagan's bend

A catalyst that is 75% one hand and 25% the mirror hand: how big is the product's lead of one hand?

A catalyst speeds up a reaction without being used up. A handed catalyst makes more of one hand of the product. Chemists measure the lead of one hand as the excess (ee, enantiomeric excess): 75 to 25 is an excess of 50% (75 minus 25). A catalyst that is all one hand gives a product with some best excess; call that 100% here.

Your guess: the product's excess of one hand

Pick one first.

Question 2 of 3 · a molecule that copies its own hand

Start with a head start of five parts in ten million. After three runs, how much of one hand?

In 1995 Kenso Soai's group showed a reaction whose product is the catalyst for making more of itself, copies its own hand, and pulls further ahead each time (his first self-copying reaction, in 1990, lost its lead instead). In 2003 they started it with an almost even mix: an excess of one hand of only 0.00005%, prepared on purpose. That is five parts in ten million. Each run's product was the start of the next run.

Your guess: the excess of one hand after three runs

Pick one first.

Question 3 of 3 · the mirror race

Start perfectly balanced. Run it 1,000 times. What do you get?

Now take a toy reaction that starts with no handed molecules at all. Plain molecules slowly turn into one hand or the mirror hand at the same rate. Each handed molecule copies its own hand. And when a molecule meets its mirror image, the two lock into an idle mixed pair (chemists call this mutual antagonism). Nothing favours either hand.

Your guess: over 1,000 runs, you get…

Pick one first.

Why it matters

Medicines, and a very old question

Many medicines come in two mirror forms. The Nobel Committee's popular explanation says one form can have the effect you want, while the mirror form can cause unnecessary and sometimes harmful side effects. So chemists need reactions that make one hand on purpose, and Kagan's non-linear effects help them understand and tune those reactions.

Life itself is one-handed: your proteins use one hand of each amino acid. How that began is still open. Soai's reaction shows that a flask can pick a hand by chance and keep it, but the Committee is clear that this kind of model is not an answer to the origin of biological homochirality.

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