[tomothyengel]

I've been considering the linear combinations of three p orbitals to form molecular orbitals with sigma symmetry (I've been think about this in the context of modelling square planar molecules). I've found that the combination of the type + + - or + - - are not permitted. These would form a molecular orbital which is partially bonding and partially antibonding, but why is it that this configuration is not permitted.

I can sort of see that it may be something related to the symmetry and how it's not a suitable alternating pattern like + + + or + - + but I'd like to understand why they have to have such patterns to form suitable linear combinations. My mathematical knowledge is limited to hydrogen-like wavefunctions, so I'm not familiar with any of the mathematics of MO theory, but I'm willing to learn!