Reaction mechanisms
About this app
Drag the electron arrows yourself: from the electron pair to the electron-poor atom. A correct move plays the step in 3D, a wrong one gets a reason. Bromine and ethene, bromination of benzene, chlorination of methane, SN1 and SN2, with energy profile, SE/SN/SR comparison and a test mode for the Abitur.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
One rule for many mechanisms
Organic reaction mechanisms share one logic. A curved arrow shows where electrons move: it starts at an electron pair, such as a π bond or a lone pair, and ends where a new bond or a new lone pair forms. In polar steps a pair moves from electron-rich to electron-poor. In radical steps electrons move singly, which a half arrow shows. If you can read partial charges, you can derive the next step instead of memorising it.
What the app shows
Ball-and-stick models in element colours show the electrophilic addition of bromine to ethene with the bromonium ion and backside attack, the bromination of benzene with FeBr₃ with the sigma complex and rearomatisation, and the chlorination of methane with initiation, chain and termination. SN1 and SN2 with Walden inversion and the carbenium ion are included as an extra. For every step a ball moves along the energy profile. For the radical chain, the levels are calculated from bond enthalpies.
What you can try
Grab a glowing electron pair and drag the arrow onto an atom. If the move is right, the step plays in 3D. If not, the app gives the reason, for example why an arrow to the δ− bromine does not fit or why benzene wants to keep its aromaticity. The comparison view puts SE, SN and SR side by side. In test mode the app stops in the middle of a mechanism and asks: which step comes next?
Frequently asked questions
- What does a curved arrow mean in a reaction mechanism?
- It shows the movement of electrons. The arrow starts at an electron pair and ends where a new bond or a new lone pair forms. A half arrow stands for a single electron.
- Why does benzene react with bromine by substitution rather than addition?
- Addition would destroy the aromatic system for good, and benzene would lose its resonance energy of about 150 kJ/mol. Losing H⁺ from the sigma complex closes the aromatic ring again, so substitution is the more favourable route.
- What is the difference between SN1 and SN2?
- In SN2 the nucleophile attacks from the back while the leaving group departs: one step with Walden inversion. In SN1 the leaving group goes first, forming a carbenium ion that can then be attacked from both sides.
- Can I draw the arrows myself in the app?
- Yes. You drag the arrow from the electron pair to its target. A correct move plays the step, a wrong one gets a reason. The Next button shows the step if you get stuck.
Subject: Chemistry
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