Claisen rearrangement: push the electrons yourself
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You just pushed every arrow of the Claisen rearrangement.
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Organic Chemistry 2 · Free interactive demo
Heat allyl vinyl ether to about 180 °C and it rearranges to pent-4-enal, a γ,δ-unsaturated aldehyde. Six electrons move together through a chair-like six-membered transition state in a concerted [3,3]-sigmatropic shift.
Draw all three arrows above, then choose Next to see the product. The three practice arrows represent one concerted event, not three separate reaction steps. Each arrow is checked as you draw it, and Hint reveals the next move a little at a time.
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With the Arrow Lab student plan you can snap a photo of a reaction from your lecture notes or textbook. Arrow Lab reads the starting materials and reagents, you check that reading, and it builds the mechanism as an exercise like the one above: you draw each arrow, get hints when you are stuck, and see right away whether each move is correct.
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The Claisen rearrangement: one concerted shift, then the product
Follow C1=C2–O3–C4–C5=C6 around the six-membered transition state: the C1=C2 π electrons form the new C1–C6 σ bond, the C5=C6 π electrons shift to C4–C5, and the O3–C4 σ bond breaks as its electrons form C2=O3. Both π bonds shift without ions or intermediates. Forming the strong C=O bond drives the rearrangement to pent-4-enal.
The 2 steps of the demo, in the exercise's own words. Try drawing each one above before you read it.
Concerted [3,3]-sigmatropic shift through a chair-like transition state
Heating makes the six atoms C1=C2–O3–C4–C5=C6 reorganize in a single cyclic six-electron step. A new C1–C6 σ bond forms while the O3–C4 σ bond breaks. Both π bonds shift. No ions or intermediates form, and the strong C=O bond that results drives the reaction forward.
Pent-4-enal
The product is the γ,δ-unsaturated aldehyde pent-4-enal. C=C plus C–O bonds have been traded for C–C plus C=O bonds, which makes the rearrangement thermodynamically favourable.
How the mechanism is drawn
heat (180 °C), neat