3D models are useful because they allow you
to see much more of the 3-dimensional aspects of a molecule than is obvious
with a structural formula such as HOCH2CH(CH3)CH2CH3.
The molecular viewing gallery allows you to see a number of molecules in 3D
perspective and to rotate them (you will need the plug-in Chime). It is important
to remember, however, that the conformation of atoms that you see in these
molecule is not static; that is, rotation of groups about single bonds can
lead to an arrangement of atoms that is not the same as the picture you see.
Let's go to the Molecular Viewing Gallery at http://www.dcu.ie/%7Echemist/pratt/pdb/gallery.htm,
and click on 2-methylbutan-1-ol.
First, write a structural formula of the
type shown above for this compound.
Does this compound exhibit optical isomerism?
Does this compound exhibit geometrical
isomerism?
Rotate the molecule until the OH group
is on the right-hand side and vertical. Now draw a structure for the molecule
as it would appear after you have rotated the ethyl group around the single
bond between the second and third carbons. Is the number 4 (end) carbon
closer to the oxygen now or farther away? Is this new arrangement of atoms
a structural isomer of the compound as it is shown or is it a conformation?
Now write a structural formula for the
structural isomer of this compound.