# Position of nodal planes in molecular orbitals

From the attached picture (MO diagram of cyclopentadienyl anion) I can figure out where the nodal planes are, but why are they exactly at these positions?

Why is this nodal plane invalid?

• The picture is not quite right. As these are all pi orbitals, you have to add one nodal surface (in this case a plane) to what it says there. This plane is identical for all orbitals. – Martin - マーチン Aug 15 '14 at 19:23
• I believe that the figure you added has a higher energy than any of the others. So if it is possible, it would be an anti-bonding orbital. – LDC3 Aug 16 '14 at 0:39
• How do you know that? – RBW Aug 16 '14 at 8:47

• @Marko the molecule is of $D_{5h}$ symmetry, with a $C_5$ symmetry axis passing through the centre of the ring perpendicular to the carbon plane. This axis is accompanied by five vertical mirror planes. It can be shown, that these mirror planes are also the nodal planes for high lying orbitals. In the case you explain it would break this symmetry. – Martin - マーチン Aug 15 '14 at 19:30