The group of C[NH 2 ] 3 -compounds consists of three plastic ionic molecular crystals built up of a C[NH 2 ] 3 - Most theoretical studies on piezoelectricity have focused on inorganic materials or polymers. While piezoelectric properties of some molecular crystals have been investigated , microscopic insight into piezoelec-tric mechanisms for these materials is vital for designing new and better materials. Plastic crystals are molecular crystals characterized by the existence of orientationally disordered mesophases, triggered by the onset of rotational motion. In this paper, we investigated how the tendency of molecules to rotate manifest as a large shear compliance and hence the potential for high shear piezoelectric response and piezoelectric anisotropy. Molecules rotate in response to mechanical or electrical stimulus, which induce polarization or unit cell deformations.