Ryszard Gawinecki

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, the DFT optimized geometries of the aggregates in chloroform solution are in agreement with the X-ray crystal structures. Wavenumbers of the stretching vibration band of the C═O group were also found indicative of the type of hydrogen bond present in the solid state.

The effect of the amino group on the spectral properties of substituted styrylpyridinium salts

Abstract Thirty-six trans -1-methyl-2- and -4-( p -aminostyryl)pyridinium perchlorates were obtained by the condensation of dimethylpyridinium salts with p -aminobenzaldehydes. In all cases, a strong absorption band was present in their UV/VIS spectra above 400 nm. The spectral parameters were not simply related to the substituent constants of the amino groups. A comparison with the respective styrylpyridinium iodides showed the anion to have no effect on the spectra. The 1-methyl-( p -aminostyryl)pyridinium salts prepared are expected to be useful materials in non-linear optics and in biological studies.

Complexation of 2,6-Bis(acylamino)pyridines with Dipyridin-2-ylamine and 4,4-Dimethylpiperidine-2,6-dione

Intermolecular hydrogen bonds between 2,6-bis(acylamino)pyridines and dipyridin-2-ylamine as well as 4,4-dimethylpiperidine-2,6-dione are responsible for relatively strong interactions between these species. Association has been found to be significantly affected by the size of acyl substituent (chemical shift of the NH proton was used as the main probe in determination of the association constants). Calculations at the DFT level of theory are in line with the experimentally observed results. Calculated energies of the interactions between the complex congeners also show the size of the substituent to affect the association. Conformational changes in the dipyridin-2-ylamine molecule are shown to adapt a geometry suitable for formation of efficient hydrogen bonding.

N-methyl-1,2-dihydro-2-benzoylmethylenequinolines: configurational dissimilarity with unmethylated congeners

Abstract Twelve 1-methyl-1,2-dihydro-2-benzoylmethylenequinolines have been synthesized and their structures elucidated by 1 H, 13 C and 15 N NMR, UV–Vis and X-ray methods. The results unambiguously show that these compounds and the corresponding 1,2-dihydro-2-benzoylmethylenequinolines both in crystalline and in solution state are the Z and E isomers, respectively. Comparison of the X-ray structures reveal that ( Z )-1,2-dihydro-2-benzoyl-methylenequinolines are less twisted as compared to their 1-methyl derivatives. This difference is caused by formation of the quasi-aromatic six-membered ring stabilized by an intramolecular hydrogen bond in unmethylated congeners, prevented by N -methylation.

4-Fluoroanilines: synthesis and decomposition

Abstract Fourteen N - and/or 2-substituted 4-fluoroanilines were prepared (the series includes N–C2-bridged compounds). Some of them were found to be thermally unstable when dissolved in chloroform. Both 19 F NMR spectra and comparison of GIAO-DFT calculated and experimental 13 C chemical shifts were used to suggest decomposition products of 4-fluoroanilines.

Substituent and temperature controlled tautomerism: multinuclear magnetic resonance, X-ray, and theoretical studies on 2-phenacylquinolines

Proton-transfer equilibria in chloroform solution of twelve 2-phenacylquinolines were studied by 1H, 13C and 15N NMR spectroscopies. The (Z)-enaminone form stabilized by an intramolecular hydrogen bond was found to prevail in all cases. Electron-donating substituents in the phenacyl part of the molecule lead to an increase of the ketimine form (to 33% for p-NMe2). Variable temperature 1H NMR measurements show that higher temperatures have the same effect. The negative logarithm values of the equilibrium constant, pKT, were found to be linearly dependent on Hammett σ substituent constants. The pKTvs. temperature correlation also has a linear character. In general, strong electron-withdrawing substituents cause transformation of the ketimine to the enaminone form to become more exothermic but values of the heat of reaction for 2-phenacylquinolines studied are not linearly dependent on σ. X-Ray data show that the strength of the internal hydrogen bond in the enaminone form increases for strong electron-withdrawing substituents. Rough estimation shows this bond to be stronger in chloroform solution than in the crystalline state. π-Electron delocalization in the six-membered quasi-ring involving the H⋯O bond is very strong. This effect is responsible for the predominance of the tautomeric enaminone form in 2-phenacylquinolines. On the other hand, semiempirical AM1 and PM3 calculations show that in the gas phase the ketimine tautomer is energetically favored in most cases.

DEVELOPMENT OF FLUORESCENCE PROBES BASED ON STILBAZOLIUM SALTS FOR MONITORING FREE RADICAL POLYMERIZATION PROCESSES

A series of 1-methyl-2-(4-aminostyryl)pyridinium perchlorates and iodides were investigated as fluorescent probes for the monitoring of the progress of free radical polymerization. The study on the changes in the fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate and during photoinitiated polymerization of a 2-ethyl-2-(hydroxymethyl)propane-1,3-diol triacrylate (TMPTA)–1-methylpyrrolidin-2-one (MP) mixture. The purpose of these studies was to find a relationship between the changes in the shape and intensity of probe fluorescence and degree of monomer conversion into polymer. The polymer formation was estimated gravimetrically or by the measurement of the degree of monomer double bond disappearance using FTIR spectroscopy.

Electron ionization mass spectra and tautomerism of substituted 2-phenacylquinolines.

Tautomerism has been studied conventionally in solutions or in the solid state. However, the importance of mass spectrometry in the gas phase was realized relatively late. 2-Phenacylquinolines are known to undergo ketimine-enaminone tautomerism. The ratio of tautomers is dependent on the nature of the phenyl ring substituent and the Hammett substituent constants sigma. Theoretical calculations indicate the presence of ketimine and enaminone tautomers in the gas phase. The electron ionization mass spectra of eight 2-phenacylquinolines (ketimine form) were recorded at 70 eV in order to determine the fragmentation routes and to screen for the presence of their enaminone tautomers, (Z)-2-benzoylmethylene-1,2-dihydroquinolines, in the gas phase. The relative abundances or total ion currents of some ions correlated with the Hammett substituent constants and Hammett-Brown constants. The product ions [M-CO](+.) and [M-HCO](+) were observed. A reaction mechanism is suggested for the formation of these ions, requiring skeletal rearrangements. The results furnish information relating to tautomerism in the gas phase.

Effect of the amino group on the properties of 1-(benzylideneamino)pyridinium salts

Eleven (E)-4-t-butyl-1-(4-dimethylaminobenzylideneamino)pyridinium perchlorates were obtained by the condensation of 1-amino-4-t-butylpyridinium perchlorate with p-amino-benzaldehydes. The position of the primary band in their UV/VIS spectra was not simply related to the σ substituent constants of the different amino groups. Only two compounds were found to be fluorescent and piezochromic.

Electron impact induced fragmentation of ( p-substituted phenyl)-(4′-methylphenacyl) sulfones: contribution of sulfinate ester rearrangements

The molecular ions of the title compounds are usually very unstable. The main fragmentation corresponds to the formation of p-MeC(6)H(4)CO(+) as would be expected. Another abundant fragment ion was [M - SO(2)](+) which is formed both from the original sulfone and from the rearranged sulfinate esters. There are, however, three primary ions which can be traced back to each isomeric molecular ion: p-RC(6)H(4)SO(2)(+) to the original sulfone, p-RC(6)H(4)SO(+) to the.CH(2)S(=O)O-. type sulfinate ester and p-RC(6)H(4)OH(+.) to the.CH(2)OS(=O). type sulfinate ester of which the latter seems by far to dominate. Copyright 2000 John Wiley & Sons, Ltd.