--- title: "Alkyne reduction: Lindlar (cis) vs Na/NH₃ (trans) Template | MolDraw" url: https://www.moldraw.com/templates/alkyne-reduction-lindlar-na-nh3/ description: "Alkyne reduction: Lindlar (cis) vs Na/NH₃ (trans) template: But-2-yne gives (Z)-but-2-ene with H₂ over Lindlar’s catalyst, and (E)-but-2-ene with Na in…" 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/) › Alkyne reduction: Lindlar (cis) vs Na/NH₃ (trans) [Mechanisms](https://www.moldraw.com/templates/mechanisms/)Premium # Alkyne reduction: Lindlar (cis) vs Na/NH₃ (trans) template ![Alkyne reduction: Lindlar (cis) vs Na/NH₃ (trans) template: But-2-yne gives (Z)-but-2-ene with H₂ over Lindlar’s catalyst, and (E)-but-2-ene with Na in liquid NH₃: electron transfer gives a radical anion, which NH₃ protonates; a second electron and proton give the trans alkene.](https://www.moldraw.com/templates/alkyne-reduction-lindlar-na-nh3.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). But-2-yne gives (Z)-but-2-ene with H₂ over Lindlar’s catalyst, and (E)-but-2-ene with Na in liquid NH₃: electron transfer gives a radical anion, which NH₃ protonates; a second electron and proton give the trans alkene. ## Mechanism step by step H₂ on a poisoned Pd catalyst adds syn; dissolving sodium adds two electrons and two protons, anti 1. **Lindlar: syn addition** – H₂ on Pd/CaCO₃ poisoned with Pb(OAc)₂ and quinoline: both H add to one face; the poison stops at the alkene 2. **Electron transfer** – Na gives one electron to the π* orbital: a radical anion, with its two lobes trans to keep apart 3. **Protonation** – NH₃ protonates the carbanion carbon: a trans vinyl radical 4. **Second electron** – A second Na gives the vinyl anion, still trans 5. **Protonation** – NH₃ delivers the second H: (E)-but-2-ene ## Key points - Lindlar’s catalyst (Pd on CaCO₃ or BaSO₄, poisoned with Pb(OAc)₂ and quinoline) adds H₂ syn and is too weak to reduce the alkene: internal alkynes give cis (Z) alkenes. - Na or Li in liquid NH₃ (−33 °C) adds an electron, a proton, an electron and a proton; the vinyl radical and anion take the less hindered trans shape, so the product is the trans (E) alkene. - Per alkyne: 2 Na + 2 NH₃ → alkene + 2 NaNH₂. Terminal alkynes are deprotonated (NaNH₂) instead, so this works best on internal alkynes. - H₂ with ordinary Pd/C or Pt reduces the alkyne right through to the alkane. Drawn with 58 atoms, 14 arrows, 7 shapes – every one editable in MolDraw. ## Sources - [Wade, Organic Chemistry, 8th ed., Pearson 2013, ch. 9](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 Alkyne reduction: Lindlar (cis) vs Na/NH₃ (trans) template free? You can preview the Alkyne reduction: Lindlar (cis) vs Na/NH₃ (trans) 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 Alkyne reduction: Lindlar (cis) vs Na/NH₃ (trans) 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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