The molecular geometry, the normal mode frequencies and corresponding vibrational assignments of methylphenidate in the ground state were performed by DFT/B3LYP level of theory using the 6-311++G(d, p) basis set. Harmonic vibrational frequencies were calculated. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The conformational stabilities and optimized geometrical parameters have been carried out with density functional theory with 6-311++G(d,p) basic set by the DFT/B3LYP method. The frequency calculations have been performed with DFT to study the vibrational properties and their dependence on the molecular conformation. (C) 2008 Elsevier B.V. All rights reserved.