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Carbohydrate Conversion Basics

Aug 25, 2025

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Overview

This lecture explains how to convert D-Glucose and D-Fructose from Fischer Projections to Haworth Projections, including shortcuts and essential terminology for carbohydrate structures.

Carbohydrate Basics

  • Simple carbohydrates can be represented as Fischer Projection, Chair Conformation, or Haworth Projection.
  • Fischer Projections simplify the 3D arrangement of chiral centers into 2D.
  • D-Glucose is an aldohexose (6-carbon sugar with an aldehyde group).
  • D-Fructose is a ketohexose (6-carbon sugar with a ketone group).

Fischer Projections for D-Glucose and D-Fructose

  • D-Glucose Fischer layout: chiral centers have side groups in the pattern right, left, right for OH placement.
  • The lowest chiral carbon's OH is right for D-Glucose, left for L-Glucose.
  • D-Fructose Fischer layout mirrors D-Glucose (right, left, right pattern for OHs).

Formation of Cyclic (Haworth) Structures

  • Sugars convert between linear (Fischer) and ring (Haworth) forms.
  • For glucose, nucleophilic attack: oxygen on C5 attacks the carbonyl carbon (C1), forming a six-membered pyranose ring.
  • For fructose, oxygen on either C5 (forms five-membered furanose) or C6 (forms six-membered pyranose) attacks the carbonyl on C2.

Shortcut for Fischer to Haworth Conversion

  • Everything on the right in Fischer drops down in Haworth; everything on the left goes up.
  • For D-sugars, CH2OH group on C6 is drawn up; for L-sugars, it's down.
  • Carbon 1 (anomeric carbon): OH down gives alpha, OH up gives beta anomer.

Anomers and Ring Types

  • Pyranose: six-membered ring (e.g., D-Glucose after C5 attacks C1).
  • Furanose: five-membered ring (e.g., D-Fructose after C5 attacks C2).
  • Beta anomer: anomeric OH up; alpha anomer: anomeric OH down.

Key Terms & Definitions

  • Fischer Projection — 2D representation of a 3D chiral molecule.
  • Haworth Projection — Flat ring diagram of a cyclic sugar.
  • Aldohexose — Six-carbon sugar with an aldehyde.
  • Ketohexose — Six-carbon sugar with a ketone.
  • Anomeric carbon — Carbon that becomes new chiral center after ring closure.
  • Pyranose — Six-membered ring formed by sugars.
  • Furanose — Five-membered ring formed by sugars.
  • Alpha (α) anomer — Anomeric OH down in Haworth.
  • Beta (β) anomer — Anomeric OH up in Haworth.

Action Items / Next Steps

  • Practice converting Fischer Projections to Haworth Projections for glucose and fructose.
  • Review quiz and cheat sheet at leah4sci.com/fischer as suggested.

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