# What is the purpose of phase matching when drawing a MO diagram?

During the lecture, we were learning how to draw the MO diagram for $$\mathrm{BF_3}$$. I understand that only orbitals with the same symmetry labels can interact and form molecular orbitals. My professor always elaborates a lot on "phase matching," and he would draw the orbitals out.

However, I do not understand how these orbital drawings are supposed to assist me when drawing the MO diagram. How would it affect my process for drawing the MO diagram?

• If I interpret correctly phase matching is guaranteed when the orbitals have matching symmetry. You are then allowed to combine them in the MO diagram. – Buck Thorn Oct 5 '19 at 19:32
• Phase matching can matter for determining whether you are forming a bonding vs an antibonding orbital. – Tyberius Oct 5 '19 at 22:58