--- title: "Reducing sugars: Benedict’s, Fehling’s and Tollens’ tests Template | MolDraw" url: https://www.moldraw.com/templates/reducing-sugar-tests/ description: "Reducing sugars: Benedict’s, Fehling’s and Tollens’ tests template: In base, β-D-glucose opens to the aldehyde; Cu²⁺ (Benedict’s or Fehling’s) is reduced to…" lang: en publisher: Scidart Academy generated: 2026-11-13 --- [MolDraw](https://www.moldraw.com/) › [Templates](https://www.moldraw.com/templates/) › [Biochemistry](https://www.moldraw.com/templates/biochemistry/) › Reducing sugars: Benedict’s, Fehling’s and Tollens’ tests [Biochemistry](https://www.moldraw.com/templates/biochemistry/)Premium # Reducing sugars: Benedict’s, Fehling’s and Tollens’ tests template ![Reducing sugars: Benedict’s, Fehling’s and Tollens’ tests template: In base, β-D-glucose opens to the aldehyde; Cu²⁺ (Benedict’s or Fehling’s) is reduced to red Cu₂O and Ag⁺ (Tollens’) to a silver mirror while C1 is oxidised to gluconate. Sucrose gives no reaction.](https://www.moldraw.com/templates/reducing-sugar-tests.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). In base, β-D-glucose opens to the aldehyde; Cu²⁺ (Benedict’s or Fehling’s) is reduced to red Cu₂O and Ag⁺ (Tollens’) to a silver mirror while C1 is oxidised to gluconate. Sucrose gives no reaction. ## Mechanism step by step The hemiacetal opens to the aldehyde, which Cu²⁺ or Ag⁺ oxidises to the carboxylate; sucrose has no hemiacetal and does not react 1. **Deprotonation** – Hydroxide removes the anomeric OH proton 2. **Ring opening** – O⁻ reforms C=O and pushes out the ring oxygen 3. **Protonation** – Water protonates O5: the free aldehyde 4. **Benedict’s / Fehling’s** – Two Cu²⁺ (citrate or tartrate complex) take 2 e⁻: red Cu₂O 5. **Tollens’ test** – Two [Ag(NH₃)₂]⁺ take 2 e⁻: a silver mirror 6. **Sucrose: negative** – Both anomeric carbons are in the glycosidic bond, so no ring can open. Acid hydrolysis first makes it positive ## Key points - A reducing sugar has a free hemiacetal (or a ketose that isomerises in base): glucose, galactose, fructose, maltose and lactose are all positive. - Benedict’s: RCHO + 2 Cu²⁺ + 5 OH⁻ → RCOO⁻ + Cu₂O + 3 H₂O. Tollens’: RCHO + 2 [Ag(NH₃)₂]⁺ + 3 OH⁻ → RCOO⁻ + 2 Ag + 4 NH₃ + 2 H₂O. - Sucrose (Glc α1↔β2 Fru) is non-reducing; boiling with acid first hydrolyses it to glucose and fructose, and the test turns positive. - Hot alkali also enolises and fragments sugars, so these equations are idealised; electron transfer to the metal is not drawn with curly arrows. Drawn with 211 atoms, 13 arrows, 10 shapes – every one editable in MolDraw. ## Sources - [Nelson & Cox, Lehninger Principles of Biochemistry, 8th ed., 2021, ch. 7](https://openlibrary.org/isbn/9781319228002) Textbook - [Berg, Tymoczko, Gatto & Stryer, Biochemistry, 9th ed., 2019](https://openlibrary.org/isbn/9781319114657) Textbook - [Benedict, Biochem. J. 1907, 2, 408](https://doi.org/10.1042/bj0020408) Original paper ## 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 Reducing sugars: Benedict’s, Fehling’s and Tollens’ tests template free? You can preview the Reducing sugars: Benedict’s, Fehling’s and Tollens’ tests 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 Reducing sugars: Benedict’s, Fehling’s and Tollens’ tests 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. ### Are the biochemical pathways drawn with structures? Yes. 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