Effect of benzoannulation on tautomeric preferences of 4,6-di(pyridin-2-yl)cyclohexane-1,3-dione.

Density functional theory (DFT) calculations at the B3LYP/6-311+G(d,p) level show that 4,6-di(pyridin-2-yl)cyclohexane-1,3-dione is a labile compound. On the other hand, its dienolimine tautomer (4,6-di(pyridin-2-yl)cyclohaxa-1,3-diene-1,3-diol) seems stable enough to be present in vacuum. Alternatively the equilibriated species are (i) dienolimine and enolimine-enaminone ((6Z)-3-hydroxy-6-(pyridin-2(1H)-ylidene)-4-(pyridine-2-yl)cyclohex-3-enone) or (ii) dienolimine, enolimine-enaminone and dienaminone ((4Z,6Z)-4,6-di(pyridin-2(1H)-ylidene)cyclohexane-1,3-dione).

Synthesis and structural characterization of substituted 2-phenacylbenzoxazoles.

1H and 13C NMR spectra of eleven 2-phenacylbenzoxazoles (ketimine form) show that their CDCl(3)-solutions contains also (Z)-2-(benzo[d]oxazol-2-yl)-1-phenylethenols (enolimine form). Intramolecular hydrogen bonding in the latter tautomer was found to be significantly weaker than that one in respective (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines. Integrals of the 1H NMR signals were used to evaluate the molar ratio of the tautomers.

Two (E)-2-({[4-(dialkylamino)phenyl]imino}methyl)-4-nitrophenols.

The slow evaporation of analytical NMR samples resulted in the formation of crystals of (E)-2-({[4-(dimethylamino)phenyl]imino}methyl)-4-nitrophenol, C(15)H(15)N(3)O(3), (I), and (E)-2-({[4-(diethylamino)phenyl]imino}methyl)-4-nitrophenol, C(17)H(19)N(3)O(3), (II). Despite the small structural difference between these two N-salicylideneaniline derivatives, they show different space groups and diverse molecular packing. The molecules of both compounds are close to being planar due to an intramolecular O-H···N hydrogen bond.

2-Methyl-4-phenyl-3,4-dihydro-quinazoline.

The title compound, C(15)H(14)N(2), was formed during the lithia-tion of 2-methyl-quinazoline with phenyl-lithium followed by hydrolysis of the inter-mediate lithium 2-methyl-4-phenyl-4H-quinazolin-3-ide. NMR spectra as well as single-crystal X-ray structural data indicate that the reaction product to have the same structure in chloro-form solution as in the crystalline state. The phenyl substituent is twisted out of the plane of the 3,4-dihydro-quinazoline ring system by 86.

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.

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.

Instability of 2,2-di(pyridin-2-yl)acetic acid. Tautomerization versus decarboxylation.

The DFT calculations at the B3LYP level with 6-311G** basis set were carried out in order to reveal whether tautomerization or decarboxylation is responsible for the instability of 2,2-di(pyridin-2-yl)acetic (DPA) and 1,8-diazafluorene-9-carboxylic (DAF) acids. The carboxyl protons in both compounds are involved in the intramolecular hydrogen bonds (the pyridine nitrogen atoms are the hydrogen bond acceptors). Although formation of two intramolecular OH · · · N hydrogen bonds in the enols of both carboxylic acids enables effective electron delocalization within the quasi rings (· · · HO - C = C - C = N), only ene-1,1-diol of DAF has somewhat lower energy than DAF itself (ΔE is ca.

(Z)-Ethyl 2-oxo-3-(1,2-dihydroquinolin-2-yl-idene)propano-ate.

Both independent mol-ecules in the asymmetric unit of the tautomeric title compound, C(14)H(13)NO(3), a synthetic product obtained from 2-lithio-methyl-quinoline and diethyl oxalate, crystallize in the enaminone form with a Z configuration around the double bond. Intra-molecular N-H⋯O hydrogen bonds occur, generating an S(6) graph-set motif. In the crystal, weak inter-molecular C-H⋯O and π-π stacking inter-actions [centroid-centroid distances = 3.

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.

N-(2-Benzoyl-4-chloro-phen-yl)-4-chloro-benzene-sulfonamide.

The title compound, C(19)H(13)Cl(2)NO(3)S, is an N-aryl-sulfonyl derivative of 2-amino-5-chloro-benzophenone. The compound is biologically active and shows potential to be utilized as an inhibitor of CCR2 and CCR9 receptor functions. In the crystal structure, there is an intra-molecular N-H⋯O hydrogen bond between the amide and carbonyl groups.

Influence of bond fixation in benzo-annulated N-salicylideneanilines and their ortho-C(=O)X derivatives (X = CH3, NH2, OCH3) on tautomeric equilibria in solution.

1H, 13C, and 15N NMR spectra show that an ortho-C(=O)X group present in the molecules of N-salicylideneanthranilamide (X = NH2), methyl N-salicylideneanthranilate (X = OCH3), N-salicylidene-o-aminoacetophenone (X = CH3), and their benzo analogues have only a minor effect on the tautomeric OH/NH-equilibrium in solution. Only two of three possible tautomers were detected. Lability of the absent form was proved by theoretical calculations.

Electron ionization mass spectra and tautomerism of 2-phenacylpyridines.

The electron ionization mass spectra of 2-phenacylpyridine (ketimine form) and its 13 derivatives substituted in the benzene ring (1an: a R = H, b 3-Me, c 4-Me, d 4-NH(2), e 3-F, f 4-F, g 4-OMe, h 4-Cl,i 4-N(CH(3))(2),j 4-NO(2), k 4-CF(3), l 4-N(CH(2))(4), m 4- Br, n 3-Br) were recorded at 70 eV to determine the fragmentation routes and to screen the presence of their enolimine tautomers, (Z-)-2-(2-hydroxy-2-phenylvinyl)pyridines in the gas phase. The total ion currents (TIC) of the ions [MH](+), [MHCO](+), 2-PyCH(2)O(+), and RC(6)H(4)CO(+) (= ArCO(+) ) showed a fair or good correlation with the Hammett s constants (R = 0.859, 0.

Developing of fluorescence probes based on stilbazolium salts for monitoring free radical polymerization processes. II.

The series of 1-methyl-4-(4-aminostyryl)pyridinium perchlorates was investigated as fluorescent probes for the monitoring of the free radical polymerization progress. The study on the changes in fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate. The purpose of these studies was to find a relationship between the structure of fluorophore and the changes in their fluorescence shape and intensity observed during the monomer conversion into polymer.

Identity double-proton transfer in (3Z)-3-hydroxy-1,4-di(quinolin-2-yl)but-3-en-2-one.

Although there is a very fast (on the NMR timescale) double-proton transfer in (1Z,3Z)-3-hydroxy-4-quinolin-2-yl-1-quinolin-2(1H)-ylidenbut-3-en-2-one (the product of the condensation of ethyl oxalate with 2lithiomethylquinoline), it is the only species present in chloroform solution. Comparison of the product of condensation of ethyl oxalate with 2lithiomethyl derivatives of pyridine (recent studies) and quinoline (present studies) shows that benzoannulation considerably affects the tautomeric equilibrium. The observed changes are not only quantitative but also qualitative.

(1Z,3Z)-1,4-Di(pyridin-2-yl)buta-1,3-diene-2,3-diol: the planar highly conjugated symmetrical enediol with multiple intramolecular hydrogen bonds.

1H, (13)C, and (15)N NMR spectral data show that in chloroform solution (1Z,3Z)-1,4-di(pyridin-2-yl)buta-1,3-diene-2,3-diol, OO, is in ca. 9:1 equilibrium with (3Z)-3-hydroxy-1,4-di(pyridin-2-yl)but-3-en-2-one, OK, while no 1,4-di(pyridin-2-yl)-2,3-butanedione, KK, was detected. The species present in the tautomeric mixture were identified by comparing their experimental chemical shifts with those known for similar compounds as well as with the theoretically calculated (GIAO-HF/DFT) values.