• Representing?3-D?molecules on a?2D?surface is not easy and the best way to understand?3-D?structures is to use modelling kits or?3-D?modelling software, such as ACD Labs ChemSketch
• For simplification, complex organic molecules are shown with 90^o?bond angles that give the minimum information of which atoms are connected together as in this representation of hexane, C₆H₁₄

A simplified displayed structure for hexane

• The true structure of hexane looks very different when viewed in 3-D modelling software
• Free rotation of the single bonds gives rise to structures that look different on paper:

Different 3-D structures for hexane

• By convention, when showing using 3-D models or drawings, carbon is black, hydrogen is white and oxygen is red
• These structures may not contain accurate?atomic radii,?bond angles?or?bond lengths?(modelling software usually allows you to manipulate these), but they convey information about the orientation of atoms that is very important in?stereochemistry
• Stereochemistry?is the study of the relative spatial arrangements of atoms in molecules

Stereochemical drawings

• To simplify?3-D?drawings, chemists use a convention of drawing 'wedge' bonds to show bonds coming out of the plane of the paper or receding away from the plane
  • A single solid line indicates the bond is in the same plane as the paper
  • The solid wedge shows the bond is coming towards you and the hatched or partial wedge bond is going away from you
• The stereochemical drawing for hexane is shown below:

A stereochemical drawing for hexane

• Stereochemical drawings are particularly useful for representing isomers and complex biomolecules such as carbohydrates and proteins