Similarities and differences between azomethines and ketimines: synthesis, materials characterization and structure of novel imines compounds

Imines (ketimines and azomethines) derived from p-dibenzoylbenzene (DB) and terephthalic aldehyde (TA) and two aromatic amines: aniline and 2,6-dimethylaniline have been investigated. Compounds were synthesized via condensation of amines with carbonyl monomers in DMA or amine solution. When using DMA as a solvent, azomethines with high yields were obtained. On the other hand, the amines used as a monomers served also as an effective solvent for the synthesis of the ketanils. This different reactivity of the aldehyde and ketone groups in DMA and in amine depends on the dehydration mechanism being dominated by a kinetic process or thermodynamic one. On the basis of FTIR, 13C and 1H NMR, UV-vis spectra, thermal characteristic and theoretical calculations conclusions are drawn regarding the similarities and differences between azomethines and ketimines.     

Theoretical study of the interaction of a proton with the O, F and Cl atoms of enflurane (CHFCl–CF2–O–CHF2)

Ab initio MP2 and density functional B3LYP calculations were performed to investigate the interaction of a proton with the O, F and Cl atoms of enflurane (CHFCl–CF₂–O–CHF₂) in the gas phase. The study included the optimized structures, proton affinities, interactions energies and thermodynamic properties of protonated enflurane. The proton affinities (PAs) of the O and Cl atoms are 154.5 and 139.8 kcal mol⁻¹, respectively, whereas PAs of five of the fluorine atoms are between 143.6 and 165.5 kcal mol⁻¹ (MP2 results). In contrast to protonation at the O and Cl atoms, protonation at each of the F atoms of enflurane reveals a striking result, it leads to a cleavage of the C–F bond and formation of an ion–dipole complex between the enfluranyl cation and neutral hydrogen fluoride. The [(enfluranyl)⁺FH] complexes are weakly bound, the SAPT-calculated interaction energy varies between −12.5 and −11.7 kcal mol⁻¹. The long range attraction in these complexes is dominated by the electrostatic term (70%), whereas the induction and dispersion components contribute by about 15% each. Protonation at the chlorine atom of enflurane does not lead to a cleavage of the C–Cl bond. For the O-protonated enflurane the results from the natural bond orbital analysis (NBO) are discussed in details.