Effective positronium(Ps) quadrupole interaction in some molecular crystals (naphthalene and hexamethylbenzene) has been measured through the anisotropic magnetic quenching of Ps. In order to reduce sample dependence and to achieve a good resolution, the two-dimensional angular correlation of annihilation radiation (2D-ACAR) technique has been used. Anisotropies in both naphthalene and hexamethylbenzene have not been detected because of the heavy positron irradiation effect.