The molecular structures and relative energies of various methyl and tert-butyl substituted naphthalenes and azulenes have been studied by DFT method ωB97XD/6-311(d, p) with dispersion correction. The relative energies of molecules and effects of steric repulsion, strain and ring distortion were estimated via the appropriate homodesmotic and isodesmic reactions. The calculated standard reaction enthalpies allowed us to estimate the magnitude of various nonbonding intramolecular interactions. The introduction of bulky tert-butyl substituents leads to significant distortions of naphthalene and azulene rings. The aromaticity of the rings had been estimated using HOMA indices. For the most distorted aromatic rings it was found that the net destabilization is more pronounced in octa-tert-butylnaphthalene than in the octa-tert-butylazulene even though the structural distortions of the rings were smaller in the former.