--- title: "Catalytic hydrogenation on a metal surface Template | MolDraw" url: https://www.moldraw.com/templates/catalytic-hydrogenation-syn-surface/ description: "Catalytic hydrogenation on a metal surface template: 1,2-Dimethylcyclohexene with H₂ over Pd gives cis-1,2-dimethylcyclohexane. In the Horiuti–Polanyi scheme…" 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/) › Catalytic hydrogenation on a metal surface [Mechanisms](https://www.moldraw.com/templates/mechanisms/)Premium # Catalytic hydrogenation on a metal surface template ![Catalytic hydrogenation on a metal surface template: 1,2-Dimethylcyclohexene with H₂ over Pd gives cis-1,2-dimethylcyclohexane. In the Horiuti–Polanyi scheme (simplified here: surface atoms drawn as Pd) H₂ dissociates to surface H atoms, one H adds to give a half-hydrogenated alkyl, then the second H adds from the same face and the alkane leaves.](https://www.moldraw.com/templates/catalytic-hydrogenation-syn-surface.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). 1,2-Dimethylcyclohexene with H₂ over Pd gives cis-1,2-dimethylcyclohexane. In the Horiuti–Polanyi scheme (simplified here: surface atoms drawn as Pd) H₂ dissociates to surface H atoms, one H adds to give a half-hydrogenated alkyl, then the second H adds from the same face and the alkane leaves. ## Mechanism step by step H₂ and the alkene bind to the metal, and both H atoms add from the metal side: syn addition 1. **H₂ adsorbs** – Schematic: H₂ binds to the metal and the H–H bond breaks to give surface Pd–H 2. **First H (half-hydrogenated)** – The alkene lies flat on the surface by one face; Pd–H adds across C=C (four-centre, syn): H to one carbon, the other bonds to the metal 3. **Second H, desorption** – The second H comes from the same (metal) face: both new C–H bonds are cis ## Key points - Syn addition: both H atoms come from the metal surface, so 1,2-dimethylcyclohexene gives cis-1,2-dimethylcyclohexane. - Heterogeneous catalysts (Pd/C, PtO₂, Raney Ni) lower the barrier; without a catalyst H₂ and alkenes do not react. Heats of hydrogenation (about −120 kJ mol⁻¹ for a disubstituted C=C) measure alkene stability. - Horiuti–Polanyi steps are reversible: the half-hydrogenated alkyl can lose an H again, which explains H/D scrambling and some C=C migration (the accepted mechanism, simplified here). - C=O, aromatic rings and esters are untouched under mild conditions; alkynes go to alkanes unless the catalyst is poisoned (Lindlar). Drawn with 62 atoms, 6 arrows, 432 shapes – every one editable in MolDraw. ## Sources - [Wade, Organic Chemistry, 8th ed., Pearson 2013, ch. 8](https://openlibrary.org/isbn/9780321768414) Textbook - [Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 23](https://openlibrary.org/isbn/9780199270293) 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 Catalytic hydrogenation on a metal surface template free? You can preview the Catalytic hydrogenation on a metal surface 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 Catalytic hydrogenation on a metal surface 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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