Abstarct: Pramipexole is one of the few drugs known to treat neurological diseases such as Parkinson's disease. In this drug, due to the existence of the chiral center, there are two spatial structures including R and S enantiomers. Between these two isomers, the R enantiomer has better performance and fewer side effects for the treatment of one of the neurological diseases. Because of the importance of separating the two spatial structures of this drug from each other, it is particularly important to understand the mechanism of the conversion of these two structures. In this dissertation, the computational methods were used to study the possible mechanisms of the conversion of the two enantiomers of the drug to each other in the gas phase and different solvents for determining of the best solvent. Three possible mechanisms were considered for conversion of structure R into S. Separation of proton from drug was studied in the first mechanism. In the first mechanism, the four anions were optimized using the B3LYP method and 6-311G (d, p) basis set. In addition to the gas phase, calculations were also performed in water, acetone, toluene, carbon tetrachloride, nitromethane, and diethyl solvents. The parameters of chemical hardness (η), ionization energy (IP) and electron search energy (EA) was considered for atoms. In the second mechanism, the separation of hydrogen molecule from the drug was studied in the mentioned solvents and the gas phase by the QST3 method and also the transition structure of the related reaction was introduced. NBO calculations were also performed in this mechanism to analyze the obtained structure. In the third mechanism, one-dimensional scan calculations were performed for three bonds in the initial structure in different solvents. In the first mechanism and for anion 1, proton separation was observed to be more difficult than other cases studied. In addition, since all the solvents have positive changes in the Gibbs free energy, no solvent is considered suitable for the proton removal reaction. In the second mechanism, among the reactions studied, it was determined that the second reaction was the most suitable reaction and solvent of nitromethane was determined as the best solvent. In the third mechanism, the second reaction and nitromethane solvent were obtained as the most suitable reaction and the most suitable, respectively. Comparing the obtained results of the three mechanisms, it was determined that the second mechanism, the separation of hydrogen molecule in the second reaction in nitromethane solvent, is the most suitable way to convert the two enantiomers of Pramipexole to each other.