Chem 112C - Haworth into Chair Conformation @UCR's Academic Resource Center

Introduction

This tutorial guides you through the process of converting Haworth projections of sugars into chair conformations. Understanding this transformation is crucial for organic chemistry students, as it helps visualize the three-dimensional structure of cyclic sugars and their stability.

Step 1: Draw the Haworth Projection

• Start with the Haworth projection of the sugar you want to analyze.
• Identify the anomeric carbon, which is typically the carbon that is part of the carbonyl group in the open-chain form.
• Ensure that you are aware of the orientation of substituents (e.g., hydroxyl groups, methyl groups) around the anomeric carbon.

Step 2: Identify Axial and Equatorial Positions

• Understand that in a chair conformation, substituents can occupy two positions: axial (up or down along the axis of the ring) and equatorial (pointing outward from the ring).
• Remember:
  • Axial positions alternate up and down around the chair.
  • Equatorial positions are more stable for larger substituents to reduce steric hindrance.

Step 3: Determine Substituent Positions

• Based on the Haworth projection, assign each substituent to either the axial or equatorial position in the chair conformation.
• For substituents on the anomeric carbon:
  • If the substituent in the Haworth projection is above the plane of the ring, it should be placed in the equatorial position in the chair.
  • If it is below, place it in the axial position.

Step 4: Draw the Chair Conformation

• Sketch the chair conformation based on the positions assigned in the previous step.
• Make sure to accurately depict the axial and equatorial positions.
• Use dashed lines to represent bonds pointing behind the plane and solid lines for bonds in front.

Step 5: Analyze Stability

• Evaluate the stability of the chair conformation:
  • Larger groups should prefer the equatorial position to minimize steric strain.
  • If a large substituent is in an axial position, it may cause 1,3-diaxial interactions, which are destabilizing.

Conclusion

Converting Haworth projections to chair conformations is a fundamental skill in organic chemistry, enhancing your understanding of sugar structures. By following these steps, you can accurately represent the spatial arrangement of substituents and assess the stability of cyclic sugars. Practice with various sugars to reinforce your skills, and consider exploring other conformational isomers for a broader understanding of molecular geometry.