Tautomeric Transformations and Reactivity of Polyfunctional Hydroxypyrimidines: III. Tautomerism of 5-Acyl Derivatives of Hydroxypyrimidines and Formation of H-bonded Complexes with Solvents

Tautomerism of 5-formyl- and 5-acetyl derivatives of pyrimidine-2,4,6-trione, 2-thioxopyrimidine-4,6-dione, and 4,6-dihidroxy-2-methylthiopyrimidine was studied by NMR, UV, and IR spectroscopy, as well as by quantum chemistry. An equilibrium mixture of exo- and endo-enols in the neutral state and the presence of the same tautomers in monoanions were found. The energies of intramolecular hydrogen bonds in the gas phase and their changes in going to solutions in water, DMSO, and chloroform were calculated. The energies of intra- and intermolecular hydrogen bonds are close to each other. This fact suggests existence in solutions of two forms: tautomers with intramolecular H bond and H-bonded complexes with the solvents studied, whose formation involves cleavage of the intramolecular H bond. Characteristics of intermolecular hydrogen bonds are determined by the relative proton-donor and proton-acceptor powers of polyhydroxypyrimidines and solvents and are almost independent of the polarity of the medium.     

Solvent Influence on Absorption Spectra and Tautomeric Equilibria of Symmetric Azomethine-Functionalized Derivatives: Structural Elucidation and Computational Studies

A new series of azomethine-functionalized compounds was synthesized from the condensation of 2-hydroxy-1,3-propanediamine and 2-thienylcarboxaldehydes in the presence of a drying agent. The derivatives were spectroscopically characterized by NMR, LC-MS, UV/Vis, IR and elemental analysis. Variable temperature ¹H-NMR (−60 to +60 °C) was performed to investigate the effect of solvent polarity; the capability of solvent to form H-bond was found to dramatically influencing the tautomerization process of the desired structures. The calculated thermochemical parameters (ΔH₂₉₈, ΔG₂₉₈ and ΔS₂₉₈) at DFT and MP2 levels of theory explained that 3 b exists in equilibrium with two tautomers. The basis of the electronic absorptions was pursued through Time-Dependent Density-Functional Theory (TD-DFT). Analysis of the structural surfaces was inspected and the molecular electrostatic potential (MEP) demonstrated that the three functionalized compounds were relatively analogous in the electronic distributions. Furthermore, the electrophilic and nucleophilic centers lying on the molecular surfaces were probably playing a key-role in stabilizing the compounds through the nonclassical C−H⋅⋅⋅π interactions and hydrogen bonding. The impact of solvent polarity on absorption spectra were investigated via solvatochromic shifts. For instance, compound 3 c displayed a gradual shift of the maximum absorption to the red area when the solvent polarity was increased, recording a 21 nm of bathochromic shift. In contrast, no significant solvent-effect on 3 a and 3 b was observed. The solvation relation was pursued between Gutmann's donicity numbers the experimental λ_max; exhibited almost positive linear performance with a minor oscillation, that ascribe to the possible weak interface between the molecules of solute and designated solvents. The bandgap energy of all products were assessed experimentally using optical absorption spectra following Tauc approach, giving −4.050 ( 3 a ), −3.900 ( 3 b ) and −3.210 ( 3 c ) eV. However, the ΔE were computationally figured out from TD-DFT simulation to be −4.258 ( 3 a ), −4.022 ( 3 b ) and −3.390 ( 3 c ) eV.     

Structure and Reactivity of Uracil Derivatives. 2. Ambident Nucleophilic Reactivity of 5-Diazouracil

On the basis of 3-21G type ab initio calculations we have studied all the possible complexes of 5-diazouracil with boron trifluoride. The most stable of these are the systems with the BF₃ coordinated at the 3, 9, and 10 positions of the heterocyclic molecule.     

Structure and Reactivity of Uracil Derivatives. Thermodynamic Stability of 5-Diazouracil

The equilibrium position in the electrocyclization of certain model diazo compounds has been calculated using ab initio calculations based on RHF/6-31G with full optimization of the geometry. It was shown that on reducing the NN bond length the position of equilibrium is displaced towards the acyclic isomer. This effect is expressed to the greatest extent in -diazocarbonyl systems to which 5-diazouracil derivatives belong. An unusual polarized electron distribution was apparent for 5-diazouracil itself, which does not correspond with the classical Lewis structure.     

Cationic Copolymerization of 2-Chloroethyl Vinyl Ether with Styrene Derivatives. III. Solvent and Catalyst Effects on Relative Reactivity

Abstract

The change in relative reactivity in the cationic copolymerization of 2-chloroethyl vinyl ether and styrene derivatives was investigated with various catalysts and solvents. p-Methoxystyrene, p-methylstyrene, and a-methyl-styrene were used as styrene derivatives. The styrene content in the co-polymer increased when a polar solvent and/or a strong catalyst was used. The change of relative reactivity in the copolymerization of 2-chloroethyl vinyl ether with styrene derivatives was much greater than that in the copolymerization between vinyl ethers or styrene derivatives. When nitro-ethane was used as a solvent, not only the polarity but also the nucleophilicity influenced the copolymer composition. The results were discussed by two energies, E^π and E_rs, which are measures of complex formation between monomer and carbonium ion, and stabilization energy in the transition state, respectively.     

Solvent and Media Effects on the Photophysics of Naphthoxazole Derivatives

The photophysical properties of 2‐phenyl‐naphtho[1,2‐d][1,3]oxazole, 2(4‐N,N‐dimethylaminophenyl)naphtho[1,2‐d][1,3]oxazole and 2(4‐N,N‐diphenylaminophenyl) naphtho[1,2‐d][1,3]oxazole were studied in a series of solvents. UV–Vis absorption spectra are insensitive to solvent polarity whereas the fluorescence spectra in the same solvent set show an important solvatochromic effect leading to large Stokes shifts. Linear solvation energy relationships were employed to correlate the position of fluorescence spectra maxima with microscopic empirical solvent parameters. This study indicates that important intramolecular charge transfer takes place during the excitation process. In addition, an analysis of the solvatochromic behavior of the UV–Vis absorption and fluorescence spectra in terms of the Lippert–Mataga equation shows a large increase in the excited‐state dipole moment, which is also compatible with the formation of an intramolecular charge‐transfer excited state. We propose both naphthoxazole derivatives as suitable fluorescent probes to determine physicochemical microproperties in several systems and as dyes in dye lasers; consequence of their high fluorescence quantum yields in most solvents, their large molar absorption coefficients, with fluorescence lifetimes in the range 1–3 ns as well as their high photostability.     

Chemistry and Structure of Diterpene Derivatives of the Kaurane Series: V. Isosteviol Anhydrides

(4,8,13)-13-Methyl-16-oxo-17-norkaurane-18-carboxylic acid (isosteviol) anhydride is synthesized, which is a first representative of bisditerpene compounds of the kaurane series. The structures of the anhydride and isosteviol chloride were studies by X-ray diffraction and quantum chemistry (AM1).     

Quantum-Chemical Studies of the Structure and Reactivity of Pyrazol-5-ones and Their Thio and Seleno Analogs: V. Effect of Electron Correlation on Tautomerism and Acidity of 1-Methylheteropyrazolones

The relative stability of tautomeric forms of 1-methyl-substituted heteropyrazolones (O, S, Se) and their gas-phase acidity were estimated by DFT calculations with various basis sets and methods of geometry optimization. The electron correlation effects make an appreciable contribution to the Gibbs free energies of their tautomers and anions, especially those containing the heavy atoms. The qualitative pattern of tautomerism in pyrazolones is essentially similar to that obtained by semiempirical and nonempirical RHF calculations: The most stable is the CH form. For hetero analogs, consideration of electron correlations effects increases the relative stability of SH (SeH) forms. The series of relative acidity of the compounds depending on the heteroatom is preserved (Se O).     

Polymerization of 2-Oxazolines. IV. The Structure and the Reactivity of 2-Substituted-2-oxazolines and Oxazolinium Perchlorates

Abstract

In order to elucidate the structure and the stability of the growing cationic end in the polymerization of 2-oxazolines, the reactions of 2-bromoethylbenzamide with silver salts such as silver perchlorate, tetrafluoroborate, nitrate, nitrite, cyanate, and acetate were investigated. The reactions with silver perchlorate and tetrafluoroborate gave the 2-phenyl-2-oxazolinium salt (intramolecular O-alkylation product) quantitatively, whereas the reaction with silver nitrate gave the corresponding alkyl nitrate (staight-chain product). For the reactions with silver nitrite, cyanate and acetate, both products were obtained. In order to elucidate the ring-opening reactivity of the oxazolinium cation, the ring-opening addition reaction of N-methyl-2-oxazolinium perchlorates with pyridine was investigated. It was found that N-methyl-2-phenyl-2-oxazolinium perchlorate was more reactive toward the nucleophilic ring-opening reaction than was N-methyl-2-methyl-2-oxazolinium perchlorate. The mutual copolymerization of 2-phenyl-2-oxazoline with the other 2-substituted-2-oxazoline such as 2-methyl-, 2-isopropyl-, and 2-benzyl-2-oxazoline indicated that the monomer reactivity ratio r₂ was much larger than unity, whereas r₁ was very much smaller. Based on these results, the influence of the structure and the reactivity of the monomer and the growing cationic end of the polymerizability of 2-oxazolines are discussed.     

Chemistry and Structure of Diterpene Compounds of the Kaurane Series: IX. Electrochemical Reactions of Isosteviol and Its Derivatives

The keto group in (4,8,13)-13-methyl-16-oxo-17-norkaurane-18-carboxylic acid (isosteviol) is not polarographically reduced in DMF. Isosteviol methyl ester and oximes, too, are not reduced under these conditions. Isosteviol oxime is oxidized electrochemically or with lead dioxide, yielding iminoxyl radical.     

水热和草酸改性对Y分子筛结构和酸性的影响

采用水热与草酸处理相结合的方法对NaY分子筛进行了超稳化和脱铝改性,并利用XRD、红外、NH3-TPD及原位红外技术测试了Y型分子筛结构和酸性.结果表明,水汽处理温度从500℃提高到600℃,Y型分子筛的晶胞常数a0从2.4729 nm降到2.4461 nm,硅铝比从4.22提高到10.35,相对结晶度从53.4%提高到84.3%.随着草酸加入量从0.04 g/g增加到0.36 g/g,总酸量从0.462 mmol/g降到0.315 mmol/g.     

Tautomerism of Aza cycles: IV. Tautomeric structure of 4,5-dihydropyrazol-5-one annelated on bond C3-C4 with piperidine cycle,and its three hydrochlorides

5-Methyl-2-phenyl-3,3a,4,5,6,7-hexahydro-2H-pyrazolo[4,3-c]pyridin-3-one has been synthesized and shown to exist in crystal as zwitterionic structure with the proton localized on the nitrogen atom in the piperidine ring and negative charge delocalized over the pyrazololate fragment. The structure of 2: 1, 1: 2, and 2: 3 hydrochlorides derived from the title compound has been determined by X-ray analysis.     

Quantum-Chemical Study of the Structure and Reactivity of Pyrazol-5-ones and Their Thio and Seleno Analogs: VI. Tautomeric and Acid-Base Properties of 3-Methyl-1-phenyl-4,5-dihydropyrazol-5-one, 3-Methyl- 1-phenyl-4,5-dihydropyrazole-5-thione,and 3-Methyl-1-phenyl-4,5-dihydropyrazole-5-selenone

The relative stabilities of tautomeric forms of 3-methyl-1-phenylpyrazol-5-one and its 5-thioxo and 5-selenoxo analogs, as well as their acid-base properties in the gas phase, were estimated in terms of nonempirical calculations and density functional theory. According to the results of both calculation methods, the CH tautomer of 3-methyl-1-phenylpyrazol-5-one is the most stable. The stabilities of the XH and CH forms of its heteroanalogs (X = S, Se) are comparable; the relative stability of the SeH (SH) tautomers increases when thermal corrections, zero-point energy, and electron correlation effects are taken into account. The two methods indicate increase in the gas-phase acidity of the title compounds on variation of the heteroatom in the series O 相似文献   

Regioselective Synthesis of 3- and 5-Functional Derivatives of Pyrazolidine. 1. Synthesis of Ketones of the Pyrazolidine Series

When 5-hydroxypyrazolidines reacted with ketones on the surface of basic adsorbents the 3-regioisomers were obtained in addition to the expected 5-oxoalkylpyrazolidines. The conditions for the regiodirection of the process have been found. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, 1566–1572, October, 2005.     

Chemistry and Structure of Diterpene Compounds of the Kaurane Series: IV.1 Acylation of Reduction Products of the Isosteviol Keto Group

Acetylation with acetic anhydride of (4,8,13)-16-hydroxy-13-methyl-17-norkaurane-18-carboxylic acid and its methyl ester, obtained by reduction of isosteviol and (4,8,13)-18-methoxycarbonyl-13-methyl-16-oxo-17-norkaurane, respectively, gives rise to (4,8,13)-16-acetoxy-13-methyl-17-norkaurane-18-carboxylic acid and (4,8,13)-16-acetoxy-18-methoxycarbonyl-13-methyl-17-norkaurane. The molecular and crystal structures of the compounds were established by X-ray diffraction.