Spectral-luminescence properties and acid-base properties of luminophores obtained from 3-iodo-7-dialkylaminocoumarins

The absorption and fluorescence spectra of the conjugate acids of 7-dialkylaminocoumarins were studied, and their pK_a ^I, pK_a ^II, and pK_a ^* values were determined. It was established with the aid of PMR data that the primary protonation generally involves the nitrogen-containing substituent in the 3 or 4 position, while the secondary protonation involves the nitrogen atom in the 7 position.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1170–1175, September, 1991.     

Acid-base properties of 1,2,5-oxadiazoles. 2. Aminofurazans

The behavior of 3-R-4-aminofurazans (R = NH₂, CH₃, OCH₃, N₃, COOH, and NO₂) in sulfuric acid solutions was studied by electronic and PMR spectroscopy. The constants of protonation (pK _aBH+) at the amino group and in the ring were calculated from the changes in the spectra. Dependences of the position of the absorption maxima corresponding to ^* transitions and the pK _aBH+ values and with the ^o substituent constants were found.See [1] for Communication 1.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 321–324, March, 1981.     

Basicity of 2-phenyl-5-R-1,3,4-oxadiazoles

We have studied the basicity of 2-phenyl-5-R-1,3,4-oxadiazoles (R = H, Me, CH₂Ph, t-Bu, CH₂Cl, CCl₃, CF₃) in aqueous sulfuric acid solutions. These compounds are weak organic bases (pK_BH ⁺ is −1.8 to −5.2). The values of pK_BH ⁺ determined on the H₀ and X acidity function scales agree well with each other. The substituent at the 5 position has a substantial effect on the basicity of the 1,3,4-oxadiazole ring. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 748–756, May, 2006.     

Polynuclear branched tetrazole systems. 3. Acidity of α,ω-ditetrazol-5-ylalkanes

α,ω-Ditetrazol-5-ylalkanes with 1 to 5 methylene groups in the alkyl fragment display the properties of dibasic heterocyclic NH acids with pK_a values lying in the range 3.4–6.1. The pK_a values of these compounds are in a linear dependence on the values of the dielectric permeability of the medium, on the chemical shifts of the signals of the endocyclic carbon atom, and of the carbon atom of the α-methylene group in the ¹³C NMR spectra. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 535–541, April. 2006.     

Protonation of pyrrolo [1,2-α] Pyrimidine derivatives

The protonation of pyrrolo [1,2-] pyrimidine and 6, 7, 8, 9-tetrahydropyrimido [1, 2-] indole derivatives in CF₃COOH (at –15 to +25° C) and in CF₃COOH/H₂SO₄ (at 25°) was studied by PMR spectroscopy. The investigated compounds form monocations, the structure of which corresponds to the addition of a proton to the carbon atom of th pyrrole fragment in the position to the bridge nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 686–692, May, 1976.     

The Protonation and Deprotonation Equilibria of Hypericin Revisited

 The protonation and deprotonation behaviour and the assignment of pK _a values of hypericin are reviewed and discussed. Three experiments (electrospray MS, ¹H NMR, acid–base indicator equilibria) provided additional evidences for the assignment of pK _a values of −5 and −6 to mono- and diprotonation at the carbonyl groups of hypericin, of pK _a = 2 to monodeprotonation at the bay-region, and of pK _a = 11 to dideprotonation at the bay- and peri-regions.     

Photophysics and Acid‐Base Chemistry of Re(CH3bpyCOOH)(CO)3X (X=Cl−, and Imidazole) Complexes

Rheniumtricarbonyl(4′‐methyl‐2,2′‐bipyridine‐4‐carboxylic acid)X (where X is Cl^? and imidazole) complexes have been prepared. These two complexes exhibit similar spectroscopic properties. The metal‐ to‐ligand charge‐transfer (MLCT) absorption and the corresponding emission are observed. This charge transfer band is highly solvent dependent. Due to the stronger electron‐withdrawing ability of the ‐COOH (in comparison to the ‐COO^? group), the MLCT band has red‐shifted during protonation. Emission quantum yields are dramatically reduced while life time remains similar upon protonation. These behaviors are typical in static quenching mechanism by protons. The ground state pK_a of Re(CO)₃ (CH₃bpyCOOH)Cl obtained from the pH titration curve of the complex absorption at 409 nm was 2.5.     

The Protonation and Deprotonation Equilibria of Hypericin Revisited

Summary.  The protonation and deprotonation behaviour and the assignment of pK _a values of hypericin are reviewed and discussed. Three experiments (electrospray MS, ¹H NMR, acid–base indicator equilibria) provided additional evidences for the assignment of pK _a values of −5 and −6 to mono- and diprotonation at the carbonyl groups of hypericin, of pK _a = 2 to monodeprotonation at the bay-region, and of pK _a = 11 to dideprotonation at the bay- and peri-regions. Received September 26, 2001. Accepted October 1, 2001     

The ESR study of the structure and reactivity of α-ketoradicals, derivatives of (CF3)3CC(O)C(O)CF3

The structure and reactivity of α-ketoradicals, derivatives of (CF₃)₃CC(O)C(O)CF₃ (1), were studied by ESR spectroscopy. The photoreduction of α-diketone1 in a solution of cyclohexane in perfluorodipentyl ether results in the formation of radicals of two types, (CF₃)₃CC(2)(O(4))·C(3)(O(6)H)CF₃ (1a) and (CF₃)₃C·C(OH)C(O)CF₃ (1b) in a ∼40∶1 ratio. The degree of delocalization of the spin density in two conformers of radical1a was calculated by the MNDO/PM3 method in the UHF approximation. It was established that radicals1a and1b are capable of reversible dimerization. The rate constant of dimerization and the enthalpy of the radical—dimer equilibrium were measured for radical1a. A decrease in the rate of dimerization of radical1a upon addition of complexing solvents ((CF₃)₃COH andp-CF₃C₆H₄CF₃) was found. The influence of the solvents on the rate of dimerization was also detected for α-ketoradical (CF₃)₃CC(O)·C(OSiMe₂Ph)CF₃ (1c). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 62–67, January, 1998.     

Quinaldine derivatives with fluorine-containing substituents and cyanine dyes based on them

Condensation of fluorine-containing anilines with paraldehyde gave quinaldine derivatives with CF₃, CF₃S, and CF₃SO₂ groups in the 6 position, from which carbocyanine, merocyanine, and styryl dyes were synthesized. Fluorine-containing groups lower the basicity of quinaldine by 0.7–2.0 pK_a units and lead to deepening of the color of the dyes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 76–78, January, 1978.     

Synthesis and Electrochemical Behavior of Some 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles

1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles are key intermediates in obtaining various heterocyclic systems including pyrazolotriazoles. We present the voltammetric behavior of these compounds in nonaqueous media, with the following para substituents grafted on the benzene ring: –N(CH₃)₂, –OH, –OCH₃, –F, –Cl, –CF₃, –NO₂, as well as of the novel compounds with –Br, –I, and –SCH₃ in the para position, in order to elucidate the influence of the various substituents on the mechanism of anodic oxidation.     

Distonic ions of the “ate” class

The gas phase synthesis, structure, and reactivity of distonic negative ions of the “ate” class are described. “Ate”-class negative ions are readily prepared in the gas phase by addition of neutral Lewis acids, such as BF₃, BH₃, and AlMe₃, to molecular anions, carbene negative ions, and radical anions of biradicals. The ions contain either localized σ- or delocalized π-type radical moieties remote from relatively inert borate and aluminate charge sites. The free radical reactivity displayed by these ions appears to be independent of the charge site. As an example, the distonic alkynyl radical (·C≡CBF₃⁻) is highly reactive and undergoes radical coupling reactions with NO₂, NO, H₂C=CH-CN, and H₂C=CH-CH₃. Radical-mediated group and atom transfers are observed with O₂, CS₂, and CH₃SSCH₃. Furthermore, H-atom abstraction reactions are observed, in accordance with the predicted high C-H bond strength of this species [DH₂₉₈(H-C₂BF₃⁻)=130.8 kcal mol⁻¹]. High level ab initio molecular orbital calculations on the prototype “ate”-class distonic ion · CH₂BH₃⁻ and its conventional isomer CH₃BH₂^·− reveal that CH₃BH₂^·− is 3.2 kcal/mol more stable than the α-distonic form. However, the calculations also show that CH₃BH₂^·− is unstable with respect to electron detachment, and only the α-distonic form ·CH₂BH₃⁻ should be experimentally observed in the gas phase.     

Palladium(II)-dppe-arylazoimidazole complexes: Synthesis,and spectroscopic characterization

Reaction of [Pd(dppe)Cl₂/Br₂] with AgOTf in a dichloromethane medium followed by ligand addition led to [Pd(dppe)(OSO₂CF₃)₂] and then [Pd(dppe)(RaaiR)](OSO₂CF₃)₂ [RaaiR′ = p-R-C₆H₄-N=N-C₃H₂-NN-1-R′, (1–3), abbreviated as a N,N′-chelator, where N(imidazole) and N(azo) are represented by N and N′, respectively; R = H (a), Me (b), Cl (c) and R′ = Me (1), CH₂CH₃ (2), CH₂Ph (3), OSO₂CF₃ is the triflate anion, dppe = 1,2-bis-(diphenylphosphinoethane)]. ³¹P “¹H” NMR confirmed that due to the two phosphorus atom interaction in the azoimine symmetrical environment one sharp peak was formed. The ¹H NMR spectral measurements suggest that azo-imine link with lot of phenyl protons in the aromatic region. ¹³C (¹H) NMR spectrum, ¹H, ¹H COSY and ¹H, ¹³C HMQC spectrum assign the solution structure and stereo-retentive conformation in each complex.     

Spectrophotometric determination of basicities of substituted acetylbiphenyls and biphenyl carboxylic acids

The basicities of several 2′-, 3′-, and 4′-substituted 4-acetylbiphenyls and biphenyl-4-carboxylic acids have been determined spectrophotometrically in sulphuric acid media at 30°C. The pK_BH ⁺ of 3′- and 4′-substituted compounds are correlated by the Hammett equation. The 4′-methoxy group deviates considerably in the Hammett plot. This is attributed to its conjugative interaction with the carbonyl or carboxyl group aided by protonation. Good correlation exists between pK_BH ⁺ and σ⁺. The basicities of 2′-substituted 4-acetylbiphenyls and biphenyl-4-carboxylic acids reaffirm the existence of π-electron steric effect of 2′substituents.     

Substituent effects on the disproportionation—combination rate constant ratios for gas‐phase halocarbon radicals,Part 5: Reactions of CF3 + CF3CH2CHCH3 and CF3CH2CHCH3 + CF3CH2CHCH3

Rate constant ratios, k_d/k_c for the disproportionation/combination reaction have been measured as 0.07 ± 0.02 when an H is removed from the CH₂ position of the CF₃CH₂CHCH₃ radical and as 0.24 ± 0.03 when the H is removed from the CH₃ position in the reaction with the CF₃ radical. For the self‐reaction between two CF₃CH₂CHCH₃ radicals, k_d/k_c has been measured as 0.27 ± 0.03 when the H is removed from the CH₂ position and as 0.47 ± 0.04 when the H is removed from the CH₃ position. The branching fraction, corrected for the number of hydrogens at each site, is 0.70 favoring the methyl position when the acceptor radical is CF₃ and 0.54 when CF₃CH₂CHCH₃ is the acceptor radical. Branching fraction results show that the CF₃ substituent on the CF₃CH₂CHCH₃ radical hinders disproportionation when CF₃ is the acceptor radical. When the accepting radical is CF₃CH₂CHCH₃ the CF₃ substituent may slightly impede the disproportionation reaction, but the branching ratio is nearly statistical. The effect of substituents on the donor radical, CF₃CH₂CHX, will be discussed for the series X = H, CF₃, Cl, and CH₃ when the acceptor radical is CF₃. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 549–557, 2001     

Modeling of Protonation Constants of Linear Aliphatic Dicarboxylates Containing -S-Groups in Aqueous Chloride Salt Solutions,at Different Ionic Strengths,Using the SIT and Pitzer Equations and Empirical Relationships

The protonation constants of ethylenedithiodiacetic, dithiodipropionic and dithiodibutyric acids were obtained from potentiometric measurements in NaCl(aq) (I≤5 mol⋅L⁻¹) and (CH₃)₄NCl(aq) (I≤3 mol⋅L⁻¹) at t=25 °C. Their dependences on ionic strength were modeled by the SIT and Pitzer approaches. The activity coefficients of the neutral species were obtained by solubility measurements. The literature values of the protonation constants of (HOOC)-(CH₂) _n -S-(CH₂) _n -(COOH) (n=1 to 3) and (HOOC)-(CH₂)-S-(CH₂) _n -S-(CH₂)-(COOH) (n=0 to 5) in NaCl(aq) and KCl(aq) (I≤3 mol⋅L⁻¹) at 18 °C were also analyzed using the above approaches. Both the log ₁₀ K _i ^H and interaction parameter values follow simple linear trends as a function of certain structural characteristics of the ligands. Examples of modeling these trends are reported. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.     

Synthesis and Electrochemical Behavior of Some 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles

Summary. 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles are key intermediates in obtaining various heterocyclic systems including pyrazolotriazoles. We present the voltammetric behavior of these compounds in nonaqueous media, with the following para substituents grafted on the benzene ring: –N(CH₃)₂, –OH, –OCH₃, –F, –Cl, –CF₃, –NO₂, as well as of the novel compounds with –Br, –I, and –SCH₃ in the para position, in order to elucidate the influence of the various substituents on the mechanism of anodic oxidation.     

Synthesis and thermal stability of silicon-containing esters of phosphorus acids

A number of trialkylsilylmethyl diphenyl phosphates MeRR′SiCH₂OP(O)(OPh)₂ (1a-e: R=Et (a), Pr (b), CF₃CH₂CH₂ (c, e), Me₃SiCH₂ (d); R′=Me (a-d), Et (e)) were synthesized and their thermal rearrangement, of the 1,2-shift type, was studied. The rearrangement consists of the migration of an alkyl group from Si atom to the methylene carbon atom and gives the corresponding silyl esters. The rate of the rearrangement was found to increase in the order1d<1b<1a<1 (R=R′=Me)<1c corresponding to the enhancement of the total inductive effect (−I) of the substituents at the Si atom. The relative migration ability of the substituents at the Si atom, determined by GC/MS analysis of the disiloxane fraction resulting from hydrolysis of pyrolyzed phosphates1a-e, increases in the order R=Pr<Et<CF₃CH₂CH₂<Me≪Me₃SiCH₂, which differs substantially from the order in which the rate of the rearrangement of phosphates1a-d changes. The electronegativity of the migrating group affects noticeably the relative ability to migrate. For Part 4, see Ref. 1. Deceased. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 1767–1772, September, 1998.     

Reactivity comparison for selenophen,thiophen, and their methyl derivatives via hydrogen-isotope exchange

Deuteration measurements have been made with t-C₄H₉OK and with 4 moles of CH₃COOH mixed with one mole of CF₃COOH against 2D-selenophen, 3D-selenophen, 3CH₃, 2D-selenophen and 5CH₃, 2D-selenophen. Reactivity in the selenohpen-thiopen series is examined via protophilic and electrophilic isotopic-exchange reactions. The factors for the partial exchange rates with acid and base for heterocyclics with D at position 2 and CH₃ at position 3, 4, or 5 are compared with those factors for isomers of monodeuterotoluene; it is found that the electronic effect of the CH₃ group is transmitted similarly for these heterocyclics and for the benzene ring. Reasonably good agreement is found between the relative constants for deuterium exchange in thiophen, selenophen, and methyl derivatives of these as catalyzed by alkali-metal t-butylates in dimethylsulfoxide (DMSO) and in t-butanol mixed with diethylene glycol dimethyl ether. This shows that the results with DMSO correctly characterize the reactivity in protophilic hydrogen exchange.     

Enamines. 9. Polarographic reduction of enamino ketones in aqueous media

The mechanism of the polarographic reduction of cyclic enamino ketones of the pyrrolidine, piperidine, and hexahydroazepine series of two types, viz., compounds in which the -carbon atom of the enamine is included in the azoheteroring, and enamino ketones in which the double bond is located outside the cyclic system, was investigated. The acyclic analogs were also studied. It is shown that the two- or four-electron reduction depends substantially on the structures of the investigated compounds and the pH of the medium; this in turn is associated with a change in the character, rate, and site of protonation of the enamino ketones and the compounds formed as a result of their reduction.See [1] for communication 8.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 357–364, March, 1981.