(1Z,3Z)-3-[Quinolin-2(1H)-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol: An unexpected most stable tautomer of 1,3-bis(quinolin-2-yl)acetone
Abstract 1 H, 13 C and 15 N NMR spectra reveal that CDCl 3 solution of 1,3-bis(quinolin-2-yl)acetone contains only ( 1Z , 3Z )-3-[quinolin-2(1 H )-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol. The proton transfer takes place between two basic centers of the molecule, which means that the process is an identity reaction by character. The situation is completely different from that detected in chloroform solution of 1,3-bis(pyridin-2-yl)acetone where three different tautomers are in equilibrium with each other. Although the proton transfers in both ( 1Z , 3Z )-3-[quinolin-2(1 H )-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol and ( 1Z , 3Z )-3-hydroxy-1-[quinolin-2(1 H )-ylidene-4-quinolin-2-yl]but-3-e…
Structure-based evaluation of the resonance interactions and effectiveness of the charge transfer in nitroamines
Structural data for five nitroamines of general formula Me2N–G–NO2 show effectiveness of the ground-state charge transfer to be most and least efficient in N,N-dimethylnitramine and in 4-N,N-dimethylamino-β-nitrostyrene, respectively. Electron-donor power of the amino nitrogen atom in the latter compound is less than that in 4-nitro-β-N,N-dimethylaminostyrene (these two compounds are isomers). Natural population analysis shows that the charge transfer from the amino to the nitro oxygen atoms is most effective in N,N-dimethylnitramine, Me2N–NO2. The nitro oxygen atoms are not the only acceptors of the negative charge lost by the amino nitrogen atom. The nitro group in two substituted nitrobe…
Tautomeric preferences of phthalones and related compounds
Abstract Multinuclear magnetic resonance and IR spectra prove that although 2-(diacylmethyl)pyridines and 2-(diacylmethyl)quinolines are β-diketones, their proton transfer product present in chloroform solution is not ketoenol but enaminone (earlier opinions were contradictory). Quinoline derivatives are less zwitterionic by character than the respective pyridyl congeners. The β-diketone form itself may also be rarely present in the solution. X-ray data show that 2-(2(1H)-pyridinylidene)-1H-indene-1,3(2H)-dione, i.e., enaminone tautomer of 2-(pyridin-2-yl)-2H-indene-1,3-dione, is also the only form present in crystal. Ab initio calculations show that the enaminone is usually more stable tha…
Self-Organization of 2-Acylaminopyridines in the Solid State and in Solution
Aggregation of 2-acylaminopyridines and their 6-methyl derivatives in chloroform solution was studied by (1)H, (13)C, and (15)N NMR spectroscopies. The results were compared with (13)C and (15)N CPMAS NMR and IR spectral as well as with X-ray structural data. Intermolecular interactions in solution and in solid state were found to have a similar nature. Relatively strong N(amide)-H···N(pyridine) intermolecular hydrogen bonds enable dimerization to take place. Steric interactions in N-pivaloyl- and N-1-adamantylcarbonyl as well as that caused by the 6-methyl group hinder formation of the dimeric aggregates stabilized by the N(amide)-H···N(pyridine) intermolecular hydrogen bonds. In general, …