--- title: "1,2- vs 1,4-addition of HBr to buta-1,3-diene Template | MolDraw" url: https://www.moldraw.com/templates/butadiene-hbr-1-2-vs-1-4-addition/ description: "1,2- vs 1,4-addition of HBr to buta-1,3-diene template: Protonation of buta-1,3-diene at C1 gives an allylic cation with positive charge on C2 and C4.…" lang: en publisher: Scidart Academy generated: 2026-11-13 --- [MolDraw](https://www.moldraw.com/) › [Templates](https://www.moldraw.com/templates/) › [Mechanisms](https://www.moldraw.com/templates/mechanisms/) › 1,2- vs 1,4-addition of HBr to buta-1,3-diene [Mechanisms](https://www.moldraw.com/templates/mechanisms/)Premium # 1,2- vs 1,4-addition of HBr to buta-1,3-diene template ![1,2- vs 1,4-addition of HBr to buta-1,3-diene template: Protonation of buta-1,3-diene at C1 gives an allylic cation with positive charge on C2 and C4. Bromide adds to C2 (1,2-addition, fastest, major at −80 °C) or C4 (1,4-addition, more stable disubstituted alkene, major at 40 °C when the addition is reversible).](https://www.moldraw.com/templates/butadiene-hbr-1-2-vs-1-4-addition.webp) [Edit in MolDraw](https://www.moldraw.com/)Download with Pro Premium template. Preview and edit it free in MolDraw; downloading and exporting it is part of [MolDraw Pro](https://www.moldraw.com/pricing). Protonation of buta-1,3-diene at C1 gives an allylic cation with positive charge on C2 and C4. Bromide adds to C2 (1,2-addition, fastest, major at −80 °C) or C4 (1,4-addition, more stable disubstituted alkene, major at 40 °C when the addition is reversible). ## Mechanism step by step One allylic cation, two products: the 1,2-adduct forms faster (kinetic), the 1,4-adduct is more stable (thermodynamic) 1. **Protonation at C1** – H⁺ adds to the end carbon so the cation formed is allylic (and secondary) 2. **Allylic cation** – The positive charge is shared by C2 and C4 3. **1,2-Addition** – Br⁻ adds at C2, next to where H⁺ went: lower barrier (C2 carries more of the charge, and Br⁻ is still close) 4. **1,4-Addition** – Br⁻ adds at C4: a disubstituted, more stable C=C ## Key points - Both products come from the same allylic cation: addition at C2 is 1,2-addition, at C4 is 1,4- (conjugate) addition. - Kinetic control (−80 °C, irreversible): the product that forms fastest wins, 3-bromobut-1-ene (about 80 %). - Thermodynamic control (40 °C): ionisation back to the allylic cation is fast, the products equilibrate and the more stable 1-bromobut-2-ene (disubstituted C=C) wins (about 80 %). - Warming the cold mixture to 40 °C converts it into the thermodynamic mixture: proof that the 1,2-adduct re-forms the cation. Drawn with 54 atoms, 10 arrows, 131 shapes – every one editable in MolDraw. ## Sources - [Wade, Organic Chemistry, 8th ed., Pearson 2013, ch. 15](https://openlibrary.org/isbn/9780321768414) Textbook - [Smith, March's Advanced Organic Chemistry, 8th ed., Wiley 2020, ch. 15](https://openlibrary.org/isbn/9781119371809) Textbook ## How to use this template 1. Press **Edit in MolDraw**. The template opens on the canvas of the free MolDraw editor. 2. Change anything: move structures, edit atoms and labels, recolour highlights or delete what you do not need. 3. Add your own structures, arrows and text next to it, or combine several templates on one page. 4. Export the drawing as PNG, SVG or PDF for slides, worksheets, theses and papers. ## Frequently asked questions ### Is the 1,2- vs 1,4-addition of HBr to buta-1,3-diene template free? You can preview the 1,2- vs 1,4-addition of HBr to buta-1,3-diene template here and open and edit it in MolDraw for free. Downloading or exporting it is part of MolDraw Pro, together with the other premium templates. ### Can I edit the 1,2- vs 1,4-addition of HBr to buta-1,3-diene template? Yes. It opens as an ordinary MolDraw drawing, so every structure, arrow, label and colour can be changed, and you can add your own content around it. ### Is the chemistry checked? Every structure is checked with RDKit and every curly arrow passes MolDraw’s electron-flow audit. The sources used are listed on this page. ### What is a curly-arrow mechanism template? A ready-made drawing of a reaction mechanism in which curved arrows show where electron pairs move in each step. 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