There is no significant change in the order of the activation energy barrier ( CN < CF 3 < P h < M e < H < tBu < OM e) and the order of stability (CN > CF 3 > P h > OM e > H > M e > tBu). The lowest activation energy barrier is 30.5 Kcal/mol that is for 4 and the highest activation energy barrier is 45.8 Kcal/mol (for 4 OM e ). For this carbene, CN substituent produces the most stable diazo derivative that is common for the other three carbenes too.