  Cremer-Pople puckering coordinates appear to be the natural candidate
variables to explore the conformational space of cyclic compounds, and in
literature different parametrizations have been used to this end. However,
while every parametrization is equivalent in identifying conformations, it is
not obvious that they can also act as proper collective variables for the
exploration of the puckered conformations free energy surface. It is shown that
only the polar parametrization is fit to produce an unbiased estimate of the
free energy landscape. As an example, the case of a six-membered ring,
glucuronic acid, is presented, showing the artefacts that are generated when a
wrong parametrization is used.
