Conformations
When the larger groups overlap they repel each other more strongly than do hydrogen, and
the potential energy goes up.
15.4 Entropy
Entropy, represented as a ∆S, is a mathematical construct that represents disorder or
probability. Natural systems want to find the lowest energy or organization possible, which
translates to the highest entropy.
A note about potential energy: If you are rusty on this, remember the analogy of a big rock
pushed to the top of a hill. At the top it has a maximum of potential energy. When you
push it and allow it to roll down the hill the potential energy stored in it is transformed into
kinetic energy that can be used to generate heat or smash something.
Notice that statistically, the ethane molecule has twice as many opportunities to be in the
gauche conformation as in the anti conformation. However, because the Gauche configu-
ration brings the methyl groups closer together in space, this generates high energy steric
interactions and do not occur without the input of energy. Thus, the butane molecules
shown will almost never be found in such unfavorable conformations.