Beside the lattice energy, vibrational entropy has an important contribution to polymorph stability. We have developed a new method (NoMoRe - Normal Mode Refinement), which allows estimating vibrational entropy from frequencies, which are obtained from calculations and refined against single crystal diffraction data. We decided to apply NoMoRe to polymorphs of 4-hydroxyacetophenone (HAP). We would like to conduct multi temperature single crystal neutron diffraction measurements on for both polymorphic forms of HAP and conduct normal mode refinements and from obtained frequencies compute vibrational entropy. Additionally in X-ray diffraction pattern for form II, at 100K we found small additional peaks in one direction. Appearance of those small satellite peaks is related to methyl group behavior. Neutrons will enable us to locate hydrogen atom positions and ADPs for methyl group of HAP.