# Using real wave functions for chemical bond explanation

My question related with another one here.

For explanation valence bond direction chemists are used real wave functions, for example $p_x, p_y, p_z, \ldots$. But this functions do not describe the preffred direction of angular momentum, they are not the eigenfunctions of $\hat L_z$. The functions, that are describe the states with some preffered directions are not real, they are complex. For hydrogen, for example, they looks like:

If some other atom nearby first one, then there is some prefered direction, and good funtcions for this situation should be not real ones, but complex ones. Then why chemists used real functions for bond explanation?

Chemists use the linear combinations of hydrogen atom wavefunctions which are real because this is simply much more convenient to think about. Notice that for hydrogen, all the orbitals for a given $n$ are degenerate, so taking these linear combinations does not affect the energy, and thus thinking about the shapes of these orbitals is potentially more useful than thinking about the shape of something which is complex.
You are correct that taking the real-valued wavefunctions causes them to no longer be eigenfunctions of $L_z$. This is a bit frustrating, but in practice we never use these orbitals for anything, so it does not really matter. I used to think organic chemists took the shape of orbitals a bit too seriously (and they maybe do), but the notion of the shape of an orbital is actually recovered in a more rigorous manner.
That is, molecular orbital theory is just a qualitative form of Hartree-Fock (HF) theory. In HF, the Fock matrix is unitarily invariant, so we are free to transform our orbitals by any unitary rotation. These orbitals can be written as functions in $\mathbb{R}^3$ as desired. Thus, there exists schemes by which molecules orbitals can be "localized" and they often take the shape of orbitals which look a whole lot like the real-valued hydrogen atom orbitals you mention.