Simple methods are proposed to estimate the boiling points and the melting points of aromatic compounds from chemical structure. The transition temperatures are, determined by the estimation of both the enthalpy and the entropy of transition. The enthalpies of boiling and melting are both estimated as additive constitutive properties. The entropy of boiling is assumed to be constant as described by Trouton’s rule, while the entropy of melting is estimated using a modification of Walden’s rule. The latter utilizes the nonadditive nonconstitutive molecular property, rotational symmetry.