The effect of substitutions (R = CF 3 , CN , H, M e, OM e, P h, tBu) to carbene 3 R is very similar to the other two carbenes discussed so far. The energy profile diagrams of carbene 3 R -N 2 reactions are presented in Figure . The nature of pre-complexes formed for different substitutions ( 3A R ) are resembling previous carbenes. There is no significant change in the qualitative nature of the energy profile diagram. The free energy change for the formation of diazo derivative (carbene -N 2 adduct which is 3B R in Figure ) is positive for all substituents as observed for the earlier two carbenes . There are few changes in the order of activation energies and stabilities of diazo derivatives of different substituents. It is observed that for this carbene, the activation energy for the CF 3 substituent is less than the CN substituent by 0.6 kcal/mol. However, the CN substituted diazo derivative is more stable than that of the CF 3 substituted diazo derivative by 2.5 kcal/mol. The lowest and highest activation energies for 3 R carbene are 29.1 kcal/mol and 39.5 kcal/mol respectively corresponds to CF 3 and OM e substituents. The most stable diazo derivative is obtained for the CN substituent and the order of stability is CN > CF 3 > tBu > P h > M e > H > OM e.