Electron Delocalization in Isocyanates, Formamides, and Ureas: Importance of Orbital Interactions

Abstract

The electron delocalization in isocyanates, amides, and ureas has been studied using ab initio MO and density functional methods. The observed trends in the CN rotational barriers and N-inversion barriers in these systems have been explained in terms of orbital interactions. NBO analysis indicates that there is nN → π*[C-X] electron delocalization in amides, which increases with a decrease in the energy difference (ΔE) between the two interacting orbitals. This phenomenon, rather than electronegativity, is responsible for the observed increase in the CN rotational barrier in amides XC(R)NH2 (R = H, NH2) in the order X = O < S < Se.