Robert Dobosz

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.

Intramolecular interactions in nitroamines studied by 1H, 13C, 15N and 17O NMR spectral and quantum chemical methods

Abstract1H, 13C, 15N and 17O NMR chemical shifts are used for the characterization of the intramolecular interactions in several nitramines of the Me2N-G-NO2 type. The charge of lone electron pair of the amino group in N,N-dimethylnitramine, N,N-dimethyl-2-nitroethenamine, N,N-dimethyl-p-nitroaniline, 4-nitro-β-dimethylaminostyrene, 4-N,N-dimethylamino-β-nitrostyrene, 4-(N,N-dimethylamino)-4′-nitrobiphenyl, and 4-(N,N-dimethylamino)-4′-nitrostilbene is transferred not only to the nitro oxygens, but also to the vinylene and benzene carbons of the G spacer and to N-methyl carbons as well. Decreased nuclear shielding is found to be qualitatively related to the decreased atomic charge around a nucleus. This finding was further verified and quantified by comparison of the NMR data with those obtained by ab initio quantum chemical calculations. 17O NMR chemical shift changes seem to be more significant when the interacting NMe2 and NO2 groups are separated by a short spacer. On the other hand, 15N NMR chemical shifts suggest that a decrease of the charge at the amino nitrogen is not related to the length of the spacer alone. A lack of the linear dependence between the 17Onitro and 15Namino chemical shifts suggests that the charge lost by the amino nitrogen was only partially gained by the oxygens in the nitro group. The increased shieldings of the aryl carbons in 4-(N,N-dimethylamino)-4′-nitrobiphenyl indicate that atoms of the p,p-biphenylene spacer also gain some charge originating from the amino nitrogen. 3JH,H spin–spin coupling constant shows that among different vinylene compounds, the charge transfer to the nitro group is practically effective only in N,N-dimethyl-2-nitroethenamine where the bond between the vinylene carbons is significantly of low order by character. The calculated Natural Population Analysis (NPA) data confirms that except the nitro oxygens, other atoms that receive the negative charge lost by NMe2 in the compounds studied are the aryl and N-methyl carbons.

Quantum chemical prediction of structure and stability of the benzodihydropyrimidine tautomers

B3LYP/maug-cc-pVTZ and MP2/maug-cc-pVTZ calculations show that 3,4-dihydro-quinazoline and its 2- and/or 4-methyl and -phenyl substituted derivatives in solution (chloroform, DMSO, methanol) are only by 0.3 kcal/mol–2.2 kcal/mol more stable than the respective tautomeric 1,4-dihydroquinazolines (the available literature experimental stability data are not coherent). In the gas phase, 2- and/or 4-substituted tautomers of 3,4-dihydroquinazoline are also energetically preferred (B3LYP/maug-cc-pVTZ, MP2/maug-cc-pVTZ and CCSD/cc-pVDZ calculations lead to the same conclusion). In vacuum, 1,4-dihydro tautomer is by 0.1 kcal/mol–0.2 kcal/mol more stable only for unsubstituted dihydro-quinazoline. The observed tautomeric preference was found almost independent on substitution and solvent used. The optimization procedure used shows that the pyrimidine ring in dihydropyrimidines studied is not planar. Noncoplanarity of the 2-phenyl ring and C=N bond in the respective compounds studied is responsible for the weakened...

Squarylium dye and onium salts as highly sensitive photoradical generators for blue light

2-Ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate was polymerized in the presence of squarylium dye and various onium salts. The onium salts under study are commercially available or may be easily synthesized and are characterized by light absorption properties below 300 nm and generate phenyl radicals upon blue light exposure. Due to these interesting properties the triacrylate polymerization can be efficiently carried out with or without the presence of any additional photoinitiator. The chemical mechanisms are investigated by steady state photolysis and nanosecond laser flash photolysis experiments. The new photoinitiators yielded a higher visible light photoinitiating polymerization effect than the commercial photoinitiator: camphorquinone/ethyl p-(dimethylamino)benzoate and camphorquinone/N-methyldiethanolamine under experimental conditions.

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). Benzoannulation of the pyridine ring at position 5,6 was found to increase the contribution of the tautomers which contain the enaminone moiety. Energies of the transition states between the stable tautomers were also calculated in order to estimate activation energy of the proton transfer. Values of the geometry based harmonic oscillator model of aromaticity (HOMA) index and Laplacian of the electron density in the hydrogen bond critical point (based on quantum theory of atom in molecules) shows that the enaminone moiety in the tautomers studied are stabilized by stronger intramolecular hydrogen bond than this present in the enolimine moiety.