The orbital phase refers to the relationship between orbitals that originates from their wave character. We show here that the orbital phase essentially determines the diastereoselectivity of the following three organic reactions. 1) Torquoselectivity of the electrocyclicring-opening reaction of 3-substituted cyclobutenes; 2) Contradictory torquoselectivity of the retro-Nazarov reaction; 3) Diastereoselectivity in electrophilic addition to substituted ethylenes.