Objectives:

At the end of this unit, the students should be able to:

1. Learn the Types of Structures

a. Sawhorse Structures

b. Newman Projections

2. Learn to draw the different Isomers

a. Sawhorse Structures

b. Newman Projections

Types of Structures

1. Two-dimensional structural formula

4. Three-dimensional structural formula

2. Condensed structural formula

5. Sawhorse structures

3. Bond-line structural formula

6. Newman Projection

Three-dimensional structural formula

Sawhorse Structures

In a sawhorse projection, the backbone carbons are represented by a diagonal line, and the terminal carbons are shown in groups.

In a staggered conformation the atoms and groups attached to each backbone carbon fit in the voids around the groups on the adjacent carbon.

In an eclipsed conformation the groups and atoms on adjacent carbons are in line with each other.

Steps in Drawing Sawhorse Structures

Draw the sawhorse projection of 1-iodo-1,2-dicholoro-2-fluoroethane in staggered conformation.

Step 1 Draw a line representing the carbon-carbon bond sloping upward and to the right.

Step 2 Then draw a bond at each carbon, one going exactly straight up and the other exactly straight down.

Step 3 Next, add the two remaining bonds at each carbon, arranged as shown to give the correct bond angles.

Step 4 Finally, add the symbols for the elements.

Exercise

Draw a sawhorse projection of 1,2-ethanediol, HO-CH2-CH2-OH in both staggered and eclipsed conformations. staggered conformation eclipsed conformation

Newman Projection

End-on representations for conformations are commonly drawn using a convention called a Newman projection. A Newman projection is a graphic that shows the three groups bonded to each carbon atom in a particular C – C bond, as well as the dihedral angle that separates them.

How to Draw a