# Dipole moment of ferrocene conformations

Which conformation of ferrocene has a zero dipole moment?

I thought that the answer should be the staggered conformation because it would have the cyclopentadienyl groups oriented away from each other. However, the answer given is the eclipsed form. I can’t understand why that happens.

• Now that's a cryptic question indeed. You are right in that the staggered conformation has zero dipole moment because of symmetry. So does the eclipsed conformation. So does every other conformation as well. – Ivan Neretin Oct 15 '17 at 18:40
• I would also argue both the eclipsed and staggered form have zero dipole-moment due to symmetry, by the argument that, if ferrocene is aligned along the z axis, then for any dipole $v = (v_x, v_y, v_z)$ there is a dipole $v' = (v_x, v_y, -v_z)$ so that the net dipole moment cancels. Maybe it is about polarizability? – logical x 2 Oct 15 '17 at 19:23

It should be easy to see that te eclipsed conformation has five planes of symmetry perpendicular to the cyclopentadienyl rings ($5\sigma_\mathrm v$). Another sixth plane of symmetry is sandwiched between the two rings and passes through the iron atom ($\sigma_\mathrm h$). The only vector that will be transformed onto itself by all these planes of symmetry is the null vector $\vec{0}$. Therefore, this conformation has zero dipole moment.
The staggered conformation also has five planes of symmetry perpendicular to the ring planes as the eclipsed conformation ($5\sigma_\mathrm v$). It also features a centre of symmetry in the iron atom ($i$) as well as improper rotation ($S_{10}$). The inversion centre alone is enough to determine that only the null vector $\vec 0$ will be transformed upon itself. Therefore, this form also has no dipole moment.