At the first project, an efficient and selective azidation of aryl halides by reacting sodium azide with aryl halides is describe. The heterogeneous nature of the copper (I) catalyst, which catalyses the cross-coupling reaction, and the antiviral and antibacterial properties of the products are features of this methodology. It is also worth noting that no aryl amines are produced as by-products under these conditions. At the second project, the non-toxic and magnetically separable nano-CuFe 2 O 4 catalyst synthesis of symmetrical aryl sulfides by the reaction of thiourea with a wide variety of aryl halide, including aryl chlorides has been reported. Excellent yields of products have been obtained under ligand-free conditions and without the use of any expensive catalysts such as palladium. At the third project, a completely green medium including water as a solvent and antiviral CuFeO 2 as a catalyst is described for the synthesis of 1,4-disubstited 1,2,3-triazoles. Excellent yields of products have been obtained under room temperature. Cost-affectivity, high stability and high recyclability of CuFeO 2 along with antiviral properties of the catalyst makes it a unique catalyst for cycloaddition of phenyl acetylene with a variety of aryl halide. At the next project, theoretical studies was investigated for aza-wittig reaction. In this work, different electron donating and electron withdrawing groups were placed on the nitrogen atom of the phosphazene moiety and relative rates of the reaction was surveyed with these substituents. Also, after showing the rate determining step of the reaction, synchronicity was studied. Calculations were performed at the levels of B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p). At the next project, a detailed study on tautomerism of diacetyl monoxime (DAMO) was performed using M06-2X/6-311++G(d,p) and B3LYP/6-311++G(d,p) levels of theory. Kinetic, thermodynamic, structural and also spectral data of the most stable tautomers of DAMO were calculated. Then, interconversion of the most stable tautomers to each other was surveyed using internal rotation and proton transfer (PT) routs through pathways A - G . Moreover, solvent effects were explored for all paths A - G . Finally, NBO analysis has been performed in order to elucidate donor-acceptor interactions in tautomers 1 - 6 . At the final project, the electronic structures, intramolecular PTs, and rotational barriers around specific bonds in the biuret isomers have been investigated at the B3LYP/6-311++G(d,p) level of theory. The results showed that biuret is nearly planar and diketo form is the most stable isomer. Furthermore, conversion of five most stable isomers to each other was also studied. The results indicated that intramolecular proton transfer step is the rate-determining step in all paths. Study of the relative stabilities and mechanism of conversion of isomers have been performed with polarizable continuum model. Moreover, NBO calculation is carried out for tautomers to obtain donor-acceptor interactions.