Converting Fischer Projections to Haworth Projections and Chair Conformations

Introduction

• Importance of converting between Fischer, Haworth, and chair conformations for the MCAT.
• Emphasis on recognizing structures to save time during exams.

Fischer Projection of D-Glucose

• D-Glucose is an aldohexose:
  • Contains an aldehyde group.
  • Has 6 carbons.
• Structure:
  • Alternates groups: right, left, right, left.
  • D means OH is on the right, L means OH is on the left.
  • Final carbon (C6) is CH2OH.
  • Carbons 1 and 6 are not fully drawn in the Fischer form.

Conversion to Haworth Projection

• Key Step: OH on carbon 5 attacks the carbonyl carbon.
• Product: Convert aldehyde to cyclic form.
• Alpha vs. Beta:
  • Alpha: OH faces down.
  • Beta: OH faces up.

Drawing the Haworth Projection

• Step 1: Draw the bonds between carbons 2 and 3.
• Step 2: Wrap the molecule around.
• Step 3: Add substituents:
  • Right side (Carbons 2-5): Drop down.
  • Left side: Remain up.
• Carbon 6: Position based on OH from carbon 5.

Mnemonic for Stability

• In Beta D-glucose, OH and CH2OH are on the same side.
• In Alpha D-glucose, OH and CH2OH are on opposite sides.

Chair Conformation

• Start with a chair skeleton: include Oxygen.
• Step 1: Identify axial and equatorial substituents.
• Step 2: Fill in substituents based on previous patterns.
• Step 3: Ensure groups are positioned correctly:
  • Carbons 2, 3, 4 drop down.
  • Carbon 6 is opposite where OH on carbon 5 was positioned.
• Stability of Beta D-glucose: All OH groups equatorial lead to stability.

D-Fructose Overview

• D-Fructose: A ketohexose with a ketone group.
• Structure:
  • 5-membered ring (Furanose).
  • CH2OH on both ends (Carbons 1 and 6).
  • Carbonyl on carbon 2.
• Follow similar patterns as D-glucose for conversion to cyclic forms.

Conclusion

• Importance of understanding the process for the MCAT.
• Practice quizzes and additional resources available at leah4sci.com/Fischer.