So far, we have seen the rotation around the carbon-carbon axis of ethane
and propane. In this exercise, we will be looking at
the rotation around the C2-C3 axis of n-butane. Going from ethane to
propane, nothing really unexpected happened; the energy profile looked quite
the same, except for the slightly larger rotational barrier in propane.
For butane however, we get a really different energy profile:
Whereas the energy profiles for rotation in ethane and propane were purely sinusoidal (i.e. only one maximum and one minimum energy, both repeated every 120°), the profile for butane contains local minima and maxima. Let's step through them, starting with the easy ones:
With this in mind, answer the question regarding the models below:
Above are four models of 1,2-dichloroethane. Which of the lines below lists the conformations in order of decreasing energy?
At this point one should keep in mind that the animation shown above is
only one particular degree of freedom for the molecule. Many more are
possible, and the actual motion of the molecule butane will be a combination
of these. To get an impression, |
The next part is the quiz!