To select an appropriate chemical to abate the reaction-free energy, the binding nature of the diazo derivative should be investigated. The effect of substitution to the carbene moiety is also analyzed to model carbenes that would be competent to produce diazo derivatives are associated with a negative free energy change. Therefore we investigate why 1 CN carbene is the affluent candidate for N 2 activation among all carbenes studied so far. From the structure of carbene 1 R presented in Figure , it is perceived that the carbene 1 R contains one C = O group which is absent from the structure of the rest of the carbenes. The impact of the C = O group on this process is yet to be brought to light. To cast more light on this matter, the molecular and electronic level inquisition is explored. The binding nature of carbene and N 2 is examined and the flow of electrons during this reaction is captured. The dominance of different substituents on the reactivity of carbene with nitrogen is also reviewed. with NHC occurs through the σ electron ( σ 2 ) donation of NHC to the π * (0) of SO 2 . The reaction of NHC with N O 2 also occurs through σ electron ( σ 2 ) donation of NHC. However, for this reaction, the N O 2 molecule is electronically excited to create a vacant σ orbital (