[en] The multiple-slit type destructive interference in molecular high-order harmonic generation (HHG) leads to the minima in the harmonic yield for particular molecular orientation angle θ_L and the harmonic order n. For the case of homonuclear diatomic molecules, we have found a condition for this destructive interference in the form of a nonlinear equation over n and θ_L. This condition strongly depends on the molecular symmetry, on the atomic orbitals of which a particular highest occupied molecular orbital (HOMO) consists and on the internuclear distance R. Therefore, one can learn about the molecular structure and dynamics analysing the HHG spectra of aligned molecules. Using the example of an Ar₂ molecule, having 5σ_u HOMO, for various internuclear distances, we analyse this interference condition and show that, in the (n, θ_L) plane, it manifests in the form of one or several continuous curves. Furthermore, in the (Rcos θ_L, λ_min) plane, where λ_min is an effective de Broglie wavelength of the recombining electron, this condition leads to a set of lines which are positioned between the limiting cases of molecular orbitals consisting of only one type (even or odd) of atomic orbitals (s and p in the Ar₂ case). (fast track communication)