Theoretical investigations on 4,4′,5,5′‐tetranitro‐2,2′‐1H,1′H‐2,2′‐biimidazole derivatives as potential nitrogen‐rich high energy materials

The ―NH₂, ―NO₂, ―NHNO₂, ―C(NO₂)₃ and ―CF(NO₂)₂ substitution derivatives of 4,4′,5,5′‐tetranitro‐2,2′‐1H,1′H‐2,2′‐biimidazole were studied at B3LYP/aug‐cc‐pVDZ level of density functional theory. The crystal structures were obtained by molecular mechanics (MM) methods. Detonation properties were evaluated using Kamlet–Jacobs equations based on the calculated density and heat of formation. The thermal stability of the title compounds was investigated via the energy gaps (?E_{LUMO ? HOMO}) predicted. Results show that molecules T5 (D = 10.85 km·s^?1, P = 57.94 GPa) and T6 (D = 9.22 km·s^?1, P = 39.21 GPa) with zero or positive oxygen balance are excellent candidates for high energy density oxidizers (HEDOs). All of them appear to be potential explosives compared with the famous ones, octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetraazocane (HMX, D = 8.96 km·s^?1, P = 35.96 GPa) and hexanitrohexaazaisowurtzitane (CL‐20, D = 9.38 km·s^?1, P = 42.00 GPa). In addition, bond dissociation energy calculation indicates that T5 and T6 are also the most thermally stable ones among the title compounds. Copyright © 2014 John Wiley & Sons, Ltd.     

Kinetics and mechanism for acid‐catalyzed disproportionation of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl

Disproportionation of cyclic nitroxyl radicals (NRs) in acid solutions is of key importance for the chemistry of these compounds. Meanwhile, the data reported on the mechanism of this reaction in dilute acids are inconsistent with those on the stability of NRs in concentrated acids. Here we have examined the kinetics and stoichiometry for the disproportionation of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl ( 1 ) in aqueous H₂SO₄ (1.0–99.3 wt%) and found that (1) the disproportionation of 1 proceeds by the same mechanism over the entire range of acid concentrations, (2) the effective rate constant of the process exhibits a bell‐shaped dependence on the excess acidity function X peaked at X = ?pK _1H+ = 5.8 ± 0.3, (3) a key step of the process involves the oxidation of 1 with its protonated counterpart 1H ⁺ yielding oxopiperidinium cation 2 and hydroxypiperidine 3 at a rate constant of (1.4 ± 0.8) × 10⁵ M^?1 · s^?1, and (4) the reaction is reversible and, upon neutralization of acid, disproportionation products 2 and 3H ⁺ comproportionate to starting 1 . In highly acidic media, the protonated form 1H ⁺ is relatively stable due to a low disproportionation rate. Based on the known and newly obtained values of equilibrium constants, both the standard redox potential for the 1H ⁺ / 3 pair (955 ± 15 mV) and the pH‐dependences have been calculated for the reduction potentials of 1 and 2 to hydroxylamine 3 that is in equilibrium with its protonated 3H ⁺ and deprotonated 3 ^? forms. The data obtained provide a deeper insight into the mechanism of nitroxyl‐involving reactions in chemical and biological systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Photoinduced electron‐transfer reactions of tris(2,2′‐bipyridine)ruthenium(II)‐based carbonic anhydrase inhibitors tethering plural binding sites

Tris(2,2′‐bipyridine)ruthenium(II) complex‐based carbonic anhydrase (CA) inhibitors, [Ru(bpy)₂(bpydbs)]²⁺ {bpy = 2,2′‐bipyridine and bpydbs = 2,2′‐bipyridinyl‐4,4′‐dicarboxilic acid bis[(2‐{2‐[2‐(4‐sulfamoylbenzoylamino)ethoxy]ethoxy}ethyl)amide]} and [Ru(bpydbs)₃]²⁺, tethering plural benzenesulfonamide groups have been prepared. The CA catalytic activity was effectively suppressed by these synthetic [Ru(bpy)₂(bpydbs)]²⁺ and [Ru(bpydbs)₃]²⁺ inhibitors, and their dissociation constants at pH = 7.2 and at 25°C were determined to be K_I = 0.93 ± 0.02 μM and K_I = 0.24 ± 0.03 μM, respectively. Next, 2 photoinduced electron‐transfer (ET) systems comprising a Ru²⁺‐CA complex and an electron acceptor, such as chloropentaamminecobalt(III) ([CoCl(NH₃)₅]²⁺) or methylviologen (MV²⁺) were studied. In the presence of CA and a sacrificial electron acceptor, such as pentaamminechlorocobalt(III) complex, the photoexcited triplet state of ³([Ru(II)]²⁺)* was quenched through an intermolecular photoinduced ET mechanism. In case of the [Ru(bpydbs)₃]²⁺‐CA‐MV²⁺ system, the photoexcited triplet state of ³([Ru(bpydbs)₃]²⁺)* was quenched by sacrificial quencher through an intermolecular photoinduced ET mechanism, giving the oxidized [Ru(bpydbs)₃]³⁺. Then the following intramolecular ET from the amino acid residue, Tyr6, near the active site of CA proceeded. We observed a transient absorption around at 410 nm, arising from the formation of a Tyr^?+ in the [Ru(bpydbs)₃]²⁺‐CA‐MV²⁺ system. These artificial Ru(II)‐CA systems may clearly demonstrate both intermolecular and intramolecular photoinduced ET reactions of protein and could be one of the interesting models of the ET proteins. Their photophysical properties and the detailed ET mechanisms are discussed in order to clarify the multistep ET reactions.     

Electroluminescence enhancement in ultraviolet organic light‐emitting diode with graded hole‐injection and ‐transporting structure

Electroluminescent intensity and external quantum efficiency (EQE) in ultraviolet organic light‐emitting diodes (UV OLEDs) have been remarkably enhanced by using a graded hole‐injection and ‐transporting (HIT) structure of MoO₃/N,N ′‐bis(naphthalen‐1‐yl)‐N,N ′‐bis(phenyl)‐benzidine/MoO₃/4,4′‐bis(carbazol‐9‐yl)biphenyl (CBP). The graded‐HIT based UV OLED shows superior short‐wavelength emis‐ sion with spectral peak of ～410 nm, maximum electroluminescent intensity of 2.2 mW/cm² at 215 mA/cm² and an EQE of 0.72% at 5.5 mA/cm². Impedance spectroscopy is employed to clarify the enhanced hole‐injection and ‐transporting capacity of the graded‐HIT structure. Our results provide a simple and effective approach for constructing efficient UV OLEDs. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

An experimental and theoretical study on the preparation of 4,4′‐methylene‐bis(N,N‐dimethylaniline) in ionic liquid

The reaction of N,N‐dimethylaniline with tetrachloromethane in ionic liquid was found to give 4,4′‐methylene‐bis (N,N‐dimethylaniline) in considerable yield. The ionic liquid was prepared from N,N‐dimethylaniline which is also the one of raw materials for the preparation of 4,4′‐methylene‐bis (N,N‐dimethylaniline), and acts as both solvent and catalyst in the reaction. Mild reaction conditions, enhanced rates, improved yields, and reagents' reactivity which is different from that in conventional organic solvents are the remarkable features observed in ionic liquids. In addition, the results of calculations are in good accordance with the experimental outcomes. Copyright © 2016 John Wiley & Sons, Ltd.     

Theoretical calculations for neighboring group participation in gas‐phase elimination kinetics of 2‐hydroxyphenethyl chloride and 2‐methoxyphenethyl chloride

Theoretical calculation of the kinetics and mechanisms of gas‐phase elimination of 2‐hydroxyphenethyl chloride and 2‐methoxyphenethyl chloride has been carried out at the MP2/6‐31G(d,p), B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(d,p), B3PW91/6‐31G(d,p) and CCSD(T) levels of the theory. The two substrates undergo parallel elimination reactions. The first process of elimination appears to proceed through a three‐membered cyclic transition state by the anchimeric assistance of the aromatic ring to produce the corresponding styrene product and HCl. The second process of elimination occurs through a five‐membered cyclic transition state by participation of the oxygen of o‐OH or the o‐OCH₃ to yield in both cases benzohydrofuran. The B3PW91/6‐31G(d,p) method was found to be in good agreement with the experimental kinetic and thermodynamic parameters for both substrates in the two reaction channels. However, some differences in the performance of the different methods are observed. NBO analysis of the pyrolysis of both phenethyl chlorides implies a C? Cl bond polarization, in the sense of C^δ+…Cl^δ?, which is a rate‐determining step for both parallel reactions. Synchronicity parameters imply polar transition states of these elimination reactions. Copyright © 2009 John Wiley & Sons, Ltd.     

Catalysis by hydrogen chloride in the gas‐phase elimination kinetics of 2‐phenyl‐2‐propanol and 3‐methyl‐1‐buten‐3‐ol

A homogeneous, molecular, gas‐phase elimination kinetics of 2‐phenyl‐2‐propanol and 3‐methyl‐1‐ buten‐3‐ol catalyzed by hydrogen chloride in the temperature range 325–386 °C and pressure range 34–149 torr are described. The rate coefficients are given by the following Arrhenius equations: for 2‐phenyl‐2‐propanol log k₁ (s^?1) = (11.01 ± 0.31) ? (109.5 ± 2.8) kJ mol^?1 (2.303 RT)^?1 and for 3‐methyl‐1‐buten‐3‐ol log k₁ (s^?1) = (11.50 ± 0.18) ? (116.5 ± 1.4) kJ mol^?1 (2.303 RT)^?1. Electron delocalization of the CH₂?CH and C₆H₅ appears to be an important effect in the rate enhancement of acid catalyzed tertiary alcohols in the gas phase. A concerted six‐member cyclic transition state type of mechanism appears to be, as described before, a rational interpretation for the dehydration process of these substrates. Copyright © 2007 John Wiley & Sons, Ltd.     

4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione in the ene reactions with cyclohexene, 1‐hexene and 2,3‐dimethyl‐2‐butene. The heat of reaction and the influence of temperature and pressure on the reaction rate

The values of the enthalpy (53.3; 51.3; 20.0 kJ mol^?1), entropy (?106; ?122; ?144 J mol^?1K^?1), and volume of activation (?29.1; ?31.0; ?cm³ mol^?1), the reaction volume (?25.0; ?26.6; ?cm³ mol^?1) and reaction enthalpy (?155.9; ?158.2; ?150.2 kJ mol^?1) have been obtained for the first time for the ene reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione 1 , with cyclohexene 4 , 1‐hexene 6 , and with 2,3‐dimethyl‐2‐butene 8 , respectively. The ratio of the values of the activation volume to the reaction volume (?V^≠_corr/ΔV_{r ? n}) in the ene reactions under study, 1 + 4 → 5 and 1 + 6 → 7 , appeared to be the same, namely 1.16. The large negative values of the entropy and the volume of activation of studied reactions 1 + 4 → 5 and 1 + 6 → 7 better correspond to the cyclic structure of the activated complex at the stage determining the reaction rate. The equilibrium constants of these ene reactions can be estimated as exceeding 10¹⁸ L mol^?1, and these reactions can be considered irreversible. Copyright © 2014 John Wiley & Sons, Ltd.     

A combined experimental and density functional study of 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes reactivity towards the allylic chlorine

Nucleophilic substitution and dehydrochlorination reactions of a number of the ring‐substituted 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes are studied both experimentally and theoretically. The developed synthetic procedures are characterized by a general rapidity, cheapness, and simplicity providing moderate to high yields of 1‐arylsulfonyl 1,3‐butadienes (48–95%), 1‐(arylsulfonyl)‐2‐R‐4‐(N,N‐dialkylamino)‐2‐butenes (31–53%), 1‐(arylsulfonyl)‐2‐R‐2‐buten‐4‐ols (37–61%), and bis[4‐(arylsulfonyl)‐3‐R‐but‐2‐enyl]sulfides (40–70%). The density functional theory B3LYP/6‐311++G(2d,2p) calculations of the intermediate allylic cations in acetone revealed their high stability occurring from a resonance stabilization and hyperconjugation by the SO₂Ar group. The reactivity parameters estimated at the bond critical points of the diene/allylic moiety display a high correlation (R² > 0.97) with the Hammett (σ_p) constants. 1‐Arylsulfonyl 1,3‐butadienes are characterized by a partly broken π conjugated system, which follows from analysis of the two‐centered delocalization (δ) and localization (λ) index values. The highest occupied molecular orbital energies of 1‐arylsulfonyl 1,3‐butadienes are lower than those of 1,3‐butadiene explaining their low reactivity towards the Diels–Alder condensation. Copyright © 2015 John Wiley & Sons, Ltd.     

Remarkable emissions in diprotonated 2,2′:6′,2″‐terpyridine derivatives

A series of new metal‐free blue emission compounds, i.e., diprotonated terpyH₂ClPF₆ ( 1 ), tterpyH₂ClPF₆ ( 2 ), ClterpyH₂ClPF₆ ( 3 ), and BterpyH₂(PF₆)₂ ( 4 ), were prepared and characterized by electrospray ionization mass spectrometry, UV–vis spectroscopy, and cyclic voltammetry (CV). Abbreviations used are terpy = 2,2′:6′,2″‐terpyridine, tterpy = 4′‐(4‐tolyl)‐2,2′:6′,2″‐terpyridine, Clterpy = 4′‐chloro‐2,2′:6′,2″‐terpyridine, and Bterpy = 4,4′,4″‐tert‐butyl‐2,2′:6′,2″‐terpyridine. The X‐ray crystal structures of the three new compounds 1, 2, and 4 were determined. Both protonated pyridine rings of the terpyridine derivatives are hydrogen bonded intermolecularly to the adjacent Cl^? ion in compounds 1 , 2, and 3 . The π–π* absorption bands in the UV region for 1, 2, 3, and 4 in acetonitrile were red‐shifted relative to those of the corresponding neutral compounds. All the compounds exhibited stronger emissions (around 400 nm) than their neutral counterparts. All the CVs for the diprotonated species, terpyH, tterpyH, ClterpyH, and BterpyH, showed the first reduction waves around ?0.6 V, which were more positive than those of the neutral ones. Density functional theory was applied to interpret the remarkable differences in the interaction of the Cl^? ion. The attachment of two protons to the two terminal Bterpy nitrogens in 4 elicits remarkable characteristics. Both positive charges on the nitrogens are delocalized over the conjugated pyridine systems and the tertiary carbonium ions are stabilized to lead to stronger emission (Φ = 0.35) than the corresponding neutral Bterpy (Φ = 0.045). CCDC 732045–732047 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif Copyright © 2010 John Wiley & Sons, Ltd.     

Theoretical design on a new double functional device of 2,2′‐bipyridine‐embedded N‐(9‐pyrenyl methyl)aza‐15‐crown‐5

Theoretical design on a new molecular switch and fluorescent chemosensor double functional device of aza‐crown ether (2,2′‐dipyridine‐embedded N‐(9‐anthraceneyl(pyrenyl)methyl)aza‐15‐crown‐5) was explored. The interactions between ligands and a series of alkaline earth metal cations (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) were investigated. The fully optimized geometry structures of the free ligands ( L _1, L ₂) and their metal cation complexes ( L ₁/M²⁺, L ₂/M²⁺) were calculated with the B3LYP/6‐31G(d) method. The natural bond orbital analysis, which is based on optimized geometric structures, was used to explore the interaction of L ₁/M²⁺, L ₂/M²⁺ molecules. The absorption spectra of L _1, L ₂, L ₁/M²⁺, and L ₂/M²⁺, and their excited states were studied by time‐dependent density functional theory. A new type molecular device L ₂(2,2′‐dipyridine‐embedded N‐(9‐pyrenyl methyl)aza‐15‐crown‐5) is designed, which not only has the selectivity for Sr²⁺, and construct allosteric switch, but also has fluorescent sensor performance.     

Lithium solvation in a PMMA membrane plasticized by a lithium‐conducting ionic liquid based on 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide

The Raman and Infrared (IR) spectra of poly(methyl methacrylate) (PMMA) membranes plasticized by ionic liquids of the (1 − x)[1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI)],xLiTFSI type, where BMI⁺ is the 1‐butyl‐3‐methylimidazolium cation and TFSI⁻ the bis(trifluoromethanesulfonyl)imide anion, are analyzed for a lithium bis(trifluoromethane sulfone)imide (LiTFSI) mole fraction x = 0.23 and PMMA contents from 0 to 50 wt%. The lithium is found to have an average coordination of about three CO groups and less than one TFSI⁻ anion. It plays the role of a cross‐linker between the ester groups of PMMA and the nonvolatile ionic liquid. Addition of PMMA to the (1 − x)(BMITFSI),xLiTFSI ionic liquid lowers the conductivity but might improve the lithium transference number by transforming the [Li(TFSI)₂]⁻ anionic clusters present in the pure ionic liquid into a mixed coordination by ester groups and TFSI⁻ anions. Copyright © 2008 John Wiley & Sons, Ltd.     

Simple near‐infrared photodetector based on charge transfer complexes formed in molybdenum oxide doped N,N′‐di(naphthalene‐1‐yl)‐N,N′‐diphenyl‐benzidine

We have demonstrated a simple near‐infrared (NIR) photodetector (PD) based on charge transfer complex (CTC) formed in molybdenum trioxide (MoO₃) doped N,N′‐di(naphthalene‐1‐yl)‐N,N′‐diphenyl‐benzidine (NPB), which shows a photocurrent of about 0.35 A/cm² at –3 V under 980 nm illumination. The existence of CTC formation promotes photocurrent generation which is investigated by comparison with MoO₃ doped 2‐methyl‐9,10‐di(2‐naphthyl)anthracene (MADN) film which has no CTC absorption. It can be evolved that this kind of simple‐structure photodetector has potential application in the near‐infrared (NIR) detection area. It is shown in this Letter that although both MoO₃ and NPB have larger energy gaps of about 3 eV and weak absorption in the NIR region, the charge transfer complexes formed by mixing the two materials show an extra absorption band and good photoelectric response in the NIR region.

     

Anion effect on the conformational equilibrium of sulfamide and its N,N′‐diindolyl derivative: Insights on anion transportation

The relatively high acidity of the sulfamide hydrogens suggests a potential for the development of sulfamide derivatives as novel anion receptors. The interactions of sulfamide with F^?, Cl^?, CH₃COO^?, and H₂PO₄^? anions were spectroscopically (¹H and ¹⁹F NMR) and theoretically (density functional theory) analyzed, and the complexation through hydrogen bonds was confirmed by changes in the NMR signals and theoretical calculations. The replacement of 2 sulfamide hydrogens with indolyl groups yields the N,N′‐diindolylsulfamide ( DIS , N‐1H‐indol‐4‐yl‐N′‐1H‐indol‐7‐ylsulfuric diamide), whose bond rotations allow the interaction of 4 H(N) atoms with anions. The conformational preferences of DIS change upon the presence of anions, but they are practically insensitive to the anion type. According to the quantum theory of atoms in molecules, natural bond orbital analysis, and NMR chemical shifts, as well as to a thermodynamic cycle, the complex with fluoride is the most stable, followed by the oxoanion‐derived models.     

Pulse radiolysis studies of 2‐ and 3‐hydroxybenzyl alcohols: inhibition of dehydration of ·OH‐(hydroxybenzyl alcohols) adducts by H2PO4− ions

Reactions of ·OH/O ^.? radicals and H‐atoms as well as specific oxidants such as Cl₂^.? and N₃· radicals have been studied with 2‐ and 3‐hydroxybenzyl alcohols (2‐ and 3‐HBA) at various pH using pulse radiolysis technique. At pH 6.8, ·OH radicals were found to react quite fast with both the HBAs (k = 7.8 × 10⁹ dm³ mol^?1 s^?1 with 2‐HBA and 2 × 10⁹ dm³ mol^?1 s^?1 with 3‐HBA) mainly by adduct formation and to a minor extent by H‐abstraction from ? CH₂OH groups. ·OH‐(HBA) adduct were found to undergo decay to give phenoxyl type radicals in a pH dependent way and it was also very much dependent on buffer‐ion concentrations. It was seen that ·OH‐(2‐HBA) and ·OH‐(3‐HBA) adducts react with HPO₄^2? ions (k = 2.1 × 10⁷ and 2.8 × 10⁷ dm³ mol^?1 s^?1 at pH 6.8, respectively) giving the phenoxyl type radicals of HBAs. At the same time, this reaction is very much hindered in the presence of H₂PO ions indicating the role of phosphate ion concentration in determining the reaction pathway of ·OH adduct decay to final stable product. In the acidic region adducts were found to react with H⁺ ions. At pH 1, reaction of ·OH radicals with HBAs gave exclusively phenoxyl type radicals. Proportion of the reducing radicals formed by H‐abstraction pathway in ·OH/O ^.? reactions with HBAs was determined following electron transfer to methyl viologen. H‐atom abstraction is the major pathway in O ^.? reaction with HBAs compared to ·OH radical reaction. H‐atom reaction with 2‐ and 3‐HBA gave transient species which were found to transfer electron to methyl viologen quantitatively. Copyright © 2010 John Wiley & Sons, Ltd.     

Isolation and characterization of conformational isomers of N,N′‐bis(3,5‐dichlorosalicylidene)‐2,2′‐ethylenedianiline: crystal structure,photoluminescence, and density functional theory calculation

We have isolated two isomeric solids 1 and 2 of N,N′‐bis(3,5‐dichlorosalicylidene)‐2,2′‐ethylenedianiline and characterized by IR, UV/Vis, X‐ray powder diffraction, thermogravimetric analysis/differential thermal analysis, and X‐ray crystallography. Although the solids are same formulas, each shows different colors and crystal structures. Orange solid ( 1 ) shows endo conformation while yellow solid ( 2 ) exhibits exo form depending on packing modes. UV/Vis spectra of 1 and 2 appear very similar patterns in the solid state; however, the bands of 1 are slightly red‐shifted compared with those of 2 . 1 displays a strong fluorescent emission band at ~582 nm while 2 shows an intense fluorescent signal at ~563 nm. The charge density populations of 1 and 2 have been studied by computational simulations using density functional theory at pbe1pbe/6‐311G** level. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energies of 1 and 2 confirm that charge transfer occurs within the organic molecules. The energy difference of HOMO‐LUMO in 1 is smaller slightly than that of 2 about 0.05 eV (~17 nm). Copyright © 2014 John Wiley & Sons, Ltd.     

Comparative studies on reaction of bis(p‐nitrophenyl) phosphate and α‐nucleophiles in cationic micellar media

We studied the cleave of bis(p‐nitrophenyl) phosphate (BNPP) over a pH range of 7.0–12.0 in the presence of cationic micelles of cetyldiethylethanolammonium bromide, cetyldimethylethanolammonium bromide, cetylpyridinium bromide, cetyltrimethylammonium bromide, and cetylpyridinium chloride by using different α‐nucleophiles, viz acetohydroxamate, benzohydroxamate, salicylhydroxamate, butane‐2,3‐dione monooximate, and α‐benzoin oximate ions. With the use of α‐nucleophiles in cationic micellar media, the hydrolytic cleavage of BNPP was found to be approximately 10⁵‐fold faster than its spontaneous hydrolysis. All reactions followed pseudo‐first‐order kinetics. The effect of various concentrations of cationic micelles for the reaction of BNPP and α‐nucleophiles has been studied. The variation of k_obs values of the reactions depends on the micellar structure, that is, head groups, hydrophobic tail length, and counter ion. Copyright © 2012 John Wiley & Sons, Ltd.     

Homo‐Diels–Alder reaction of a very inactive diene,bicyclo[2,2,1]hepta‐2,5‐diene,with the most active dienophile, 4‐phenyl‐1,2,4‐triazolin‐3,5‐dione. Solvent,temperature, and high pressure influence on the reaction rate

Solvent, temperature, and high pressure influence on the rate constant of homo‐Diels–Alder cycloaddition reactions of the very active hetero‐dienophile, 4‐phenyl‐1,2,4‐triazolin‐3,5‐dione (1), with the very inactive unconjugated diene, bicyclo[2,2,1]hepta‐2,5‐diene (2), and of 1 with some substituted anthracenes have been studied. The rate constants change amounts to about seven orders of magnitude: from 3.95^.10^?3 for reaction (1+2) to 12200 L mol^?1 s^?1 for reaction of 1 with 9,10‐dimethylanthracene (4e) in toluene solution at 298 K. A comparison of the reactivity (ln k₂) and the heat of reactions (?_r‐nH) of maleic anhydride, tetracyanoethylene and of 1 with several dienes has been performed. The heat of reaction (1+2) is ?218 ± 2 kJ mol^?1, of 1 with 9,10‐dimethylanthracene ?117.8 ± 0.7 kJ mol^?1, and of 1 with 9,10‐dimethoxyanthracene ?91.6 ±0.2 kJ mol^?1. From these data, it follows that the exothermicity of reaction (1+2) is higher than that with 1,3‐butadiene. However, the heat of reaction of 9,10‐dimethylanthracene with 1 (?117.8 kJ mol^?1) is nearly the same as that found for the reaction with the structural C=C counterpart, N‐phenylmaleimide (?117.0 kJ mol^?1). Since the energy of the N=N bond is considerably lower (418 kJ/bond) than that of the C=C bond (611 kJ/bond), it was proposed that this difference in the bond energy can generate a lower barrier of activation in the Diels–Alder cycloaddition reaction with 1. Linear correlation (R = 0.94) of the solvent effect on the rate constants of reaction (1+2) and on the heat of solution of 1 has been observed. The ratio of the volume of activation (?V^≠) and the volume of reaction (?V_r‐n) of the homo‐Diels–Alder reaction (1+2) is considered as “normal”: ?V^≠/?V_r‐n = ?25.1/?30.95 = 0.81. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of novel bis(β‐cyclodextrin)s linked with aromatic diamine and their molecular recognition with model substrates

Novel β‐cyclodextrin (β‐CD) dimers with aromatic diamine linkers, 1,3‐(aminomethyl)‐benzylamine‐bridged bis(6‐amino‐6‐deoxy‐β‐CD) (2) , 4,4′‐diaminodiphenylmethano‐bridged bis(6‐amino‐6‐deoxy‐β‐CD) (3) , and 4,4′‐ ethylenedianiline‐bridged bis(6‐amino‐6‐deoxy‐β‐CD) (4) , were synthesized. The inclusion complexation behaviors of these compounds, together with 4,4′‐aminophenyl ethyl‐bridged bis(6‐amino‐6‐deoxy‐β‐CD) (5) , with substrates such as acridine red (AR), neutral red (NR), ammonium 8‐anilino‐1‐naphthalenesulfonate (ANS), sodium 2‐(p‐toluidinyl) naphthalenesulfonate (TNS), rhodamine B (RhB), and brilliant green (BG), were investigated by ultraviolet, fluorescence, circular dichroism, and 2D NMR spectroscopy. The results indicated that the two linked CD units cooperatively bound to a guest, and the molecular binding affinity toward substrates, especially curved guest ANS and linear guests such as NR and AR, was increased. The linker length between two CD units played a crucial role in the molecular recognition of the hosts with guest dyes. The binding constants of the hosts for AR, TNS, ANS, and RhB decreased with increasing linker length in hosts 2‐4 . Moreover, structurally similar hosts 3 and 5 exhibited very different binding behavior for the guests. Host 5 showed much higher Ks values toward positively charged guests and lower Ks toward negatively charged guests than host 3 . The 2D NMR spectra of hosts 3 and 5 with RhB were acquired to understand the binding difference between 3 and 5 . The molecular binding ability and selectivity of model substrates by these hosts were sufficiently investigated to reveal not only the cooperative contributions of the linker group and CD cavities upon inclusion complexation with dye guest molecules, but also the controlling factors for the molecular selective binding. Copyright © 2008 John Wiley & Sons, Ltd.     

1,3‐Bis(2′‐hydroxyethyl)imidazolium ionic liquids: correlating structure and properties with anion hydrogen bonding ability

A series of 1,3‐bis(2′‐hydroxyethyl)imidazolium ionic liquids is reported where ¹H NMR chemical shift values and thermal stabilities (T_d), as determined by thermogravimetric analysis, are correlated with the hydrogen bonding capability of various anions ([Cl^?], [Br^?], [CF₃CO₂^?], [NO₂^?], [MsO^?], [NO₃^?], [TfO^?], [BF₄^?], [NTf₂^?], and [PF₆^?]). Use of anions with the strongest hydrogen bonding capability, such as chloride [Cl^?], bromide [Br^?], and trifluoroacetate [CF₃CO₂^?], led to the furthest observed downfield chemical shift values in DMSO‐d₆ and the poorest thermal stabilities ([CF₃CO₂^?] < 200 °C). Thermal stabilities in excess of 350 °C and upfield chemical shift values were observed for ionic liquids, which employed the weakly coordinating triflate [OTf^?], tetrafluoroborate [BF₄^?], or bis(trifluoromethylsulfonyl)imide [NTf₂^?] anion. Optimized structures of selected ionic liquids, as determined by density functional theory calculations at the B3LYP/6‐31G + (d,p) level, indicated that the anion preferred to be located above the imidazolium ring and in close proximity to the hydroxyl groups. Calculated dissociation energies (ΔE) and a comparison of key bonding distances (C2―H, (C2)H···X, O―H, and (O)H···X) also confirmed this structural preference. Copyright © 2013 John Wiley & Sons, Ltd.