Lab 5: An Exercise with Molecular Models
In this laboratory period, we will use molecular models to investigate some three-
dimensional properties of molecules. This experiment will be graded but you may work in groups.
We will look at conformations of acyclic (non-cyclic) compounds, constitutional
isomers in acyclic compounds with the same molecular formula, stereoisomers in cyclic
compounds, and identify axial and equatorial bonds in cyclohexanes. If time permits, you may
also examine other conformations of cyclohexanes.
Section 1: Conformations.
1. Ethane. Construct two models of ethane and arrange one in a fully staggered conformation
and the other in a fully eclipsed conformation.
a. Draw both of these conformations using the Newman, \"sawhorse\" and dash-
wedge drawing conventions.
b. Locate all the planes of symmetry in the two conformations of (a).
c. By how many degrees must one rotate one carbon atom with respect to the other
to carry a staggered conformation into an eclipsed conformation (or vice versa).
d. By how many degrees must one rotate one carbon atom with respect to the other
to carry one staggered conformation into another staggered conformation (or one
eclipsed conformation into another eclipsed conformation).
e. What are the H-C-C-H dihedral angles in the two conformations?
2. Propane. Replace one of the hydrogens in an ethane model with a methyl group to make
a model of propane.
a. Arrange the model in a fully staggered conformation and draw a Newman
Projection of the conformation.
