Aminimides: Rcon⊖N⊕(CH3)2CH2CH(OH)CH3(R = C6H5and CF3CF2) natural bond orbital and topological analysis of electron density distributions. Part 31
Revue Roumaine de Chimie
The negative charge in the title ylides is dispersed almost equally among the negative nitrogen, -N⊖, and the oxygen of the C=O group, as it is computationally illustrated at DFT level of theory. As result, the C-N⊖group acquires partial double bond character and, therefore, display (Z)- and (E)- diastereoisomerism of substituents around this bond. Single crystal X-ray measurements for the title aminimides reveal the preference for the (Z)- diastereomer about the CO-N⊖N⊕bond. Computationally, for example, at level B3LYP-D3/6-311+G∗∗of theory, the (E)- diastereomer is at δG298 K= 14.4 kcal/mol higher than the (Z)-aminimide 1 (R=C6H5) and with 19.9 kcal/mol higher than the (Z)- aminimides 2 (R = CF3CF2). The magnitude of the second order energy stabilization .F as a result of negative nitrogen lone pair (NNLP) charge transfer to the acceptor p∗CO is always larger for (Z)- diastereomer than for the (E)- diastereomer. Additionally, the (Z)- configuration of both aminimide 1 (R=C6H5) and aminimide 2 (R=CF2CF3) is locked by several intramolecular hydrogen bonds: OH-N⊖, CH(Me)-O=C, OH-F and HO-HC(Me), all characterized by bond critical properties (BCP) such as electron density ρ(rBCP), laplacian of electron densities ∇2(rBCP) and eigenvalues of the Hessian of the electron density λ1(rBCP), λ2(rBCP), and λ3(rBCP). Natural Bond Orbital (NBO) analysis predicts large charge transfer from the neighboring NNLP into the π∗CO. As a result, the C=O bond is lengthened in comparison with the protonated RCO- NHN. species, whereas the C-N⊖bond is shortened. Bond orders for C=O and CO-N⊖N⊕are close to 1.5. In accordance with the value of bond order, Natural Resonance Theory (NRT) analysis predicts almost equal weights for the O=C-N⊖and the ⊖O-C=N resonance structures.
Ana Racoveanu and Mircea D. Gheorghiu. "Aminimides: Rcon⊖N⊕(CH3)2CH2CH(OH)CH3(R = C6H5and CF3CF2) natural bond orbital and topological analysis of electron density distributions. Part 31" Revue Roumaine de Chimie (2020): 23-38. https://doi.org/10.33224/rrch.2020.65.1.02