- Effect of external pressure and solvent on the equilibrium constant of the Diels-Alder reaction of 9-chloroanthracene with tetracyanoethylene
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The effect of external pressure and solvent on the equilibrium constant of the Diels-Alder reaction of tetracyanoethylene with 9-chloroanthracene at 25°C was studied. The molar reaction volume is strongly solvent-dependent, cm3/mol: -11.3±1.0 in ?-xylene, -14.9±1.0 in toluene, -20.6±1.5 in 1,2-dichloroethane, -22.6±1.5 in ethyl acetate, and -24.2±1.5 in acetonitrile.
- Kiselev,Iskhakova,Shikhab,Konovalov
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- Photoinduced Electron Transfer between Acenaphthylene and Tetracyanoethylene: Effect of Irradiation Mode on Reactivity of the Charge-Transfer Complex and the Resulted Radical Ion Pair in Solution and Crystalline State
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The mechanism of photodimerization of acenaphthylene (ACN) and of reactions with tetracyanoethylene (TCNE) by electron transfer (ET) has been investigated in solution and solid state to elucidate the role of the radical cation of ACN (ACN+?) in formation of the cisoid-dimer (cisoid-1) and the transoid-dimer (transoid-1) of ACN and addition products to TCNE. Selective excitation of the 1:1 charge-transfer (CT) complex between ACN and TCNE with light of >500 nm did not result in any reaction in acetonitrile (AN) or 1,2-dichloroethane (DCE). On the other hand, direct irradiation of ACN with light of >400 nm in solution in the presence of TCNE gave cisoid-1 and transoid-1 as the major products together with a [2 + 2]-adduct (2) and two isomeric [2 + 2 + 2]-adducts (3 and 4) of ACN and TCNE as minor products. Distinction of photochemical reactivity between selective CT excitation and direct excitation of ACN can be attributed to faster backward electron transfer (BET) from the contact radical ion pair (CIP) on CT excitation than from the solvent-separated radical ion pair (SSIP) on direct excitation of ACN due to very low energy for BET, as low as 1.34 V. Effect of [TCNE] on quantum yield for the dimerization of ACN and on the cisoid / transoid ratio of the resulted 1 rationalizes the mechanism involving the singlet and triplet SSIP; the former tends to undergo BET, but the latter undergoes dissociation to ACN+?, followed by formation of dimeric radical cation of ACN, ACN2+?, finally leading to 1. A possible mechanism for formation of 3 and 4 is discussed on the basis of concentration dependence of ACN. Contrary to photochemical inertness of the CT complex in solutions, CT excitation of the 1:1 crystal of ACN and TCNE (ACN·TCNE) gave 2 as the sole product. The selective formation of 2 indicates that fixation of the two alkenic C=C double bonds in ACN·TCNE separated by 3-4 A in both the excited CT state and the resulted CIP retards the deactivation and BET but enables them to undergo cycloaddition.
- Haga, Naoki,Nakajima, Hiroyuki,Takayanagi, Hiroaki,Tokumaru, Katsumi
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- Synthesis of tetracyanoethylene by oxidative dimerization of malononitrile
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A simple laboratory procedure has been proposed for the synthesis of tetracyanoethylene in up to 54% yield by oxidative dimerization of malononitrile in the presence of selenium(IV) oxide.
- Kachanov,Slabko, O. Yu.,Kaminskii
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- Structure of Spurs in γ-Irradiated Alcohol Matrices Determined by Electron Spin-Echo Method
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Paramagnetic relaxation rates of radiation-generated tetracyanoethylene anion radicals (TCNE(1-)) and chemically prepared TCNE(1-) in the glassy matrices of ethanol, 1-propanol and 1-butanol, and radiation-generated CH3CHOH radicals in neat ethanol matrices have been measured by an electron spin-echo method for elucidating the detailed structure of spurs generated in the alcohol matrices γ-irradiated at 77 K.The local concentrations of hydroxyalkyl radicals generated in pair with TCNE(1-) or CH3CHOH radicals in isolated spurs were determined by analyzing the rates of excitation transfer from the magnetically excited TCNE(1-) or CH3CHOH radicals to the hydroxylakyl radicals.Comparison of the local concentrations of CH3CHOH radicals in ethanol matrices with and without solute tetracyanoethylene reveaked that the average number of ion pairs in a spur is close to unity.The distribution function of the distance r between TCNE(1-) and the paired hydroxyalyl radical, φ(r), was derived from relaxation kinetics of TCNE(1-), and was found to be expressed by φ(r)=3 exp(-r6/r06)(2?3/2r03).The average distances between TCNE(1-) and the paired hydroxyalkyl radicals were determined from the local concentrations of the hydroxyalkyl radicals, and were about 5 nm for all the alcohol matrices.
- Ichikawa, Tsuneki,Wakasugi, Shin-ichi,Yoshida, Hiroshi
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- Electronic, infrared, mass spectrometry and thermal studies on the reaction of 2-amino-6-methylpyridine with π-acceptors
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The spectrophotometric characteristics of the solid charge-transfer molecular complexes (CT) formed in the reaction of the electron donor 2-amino-6-methylpyridine (2A6MPy) with the π-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzoq
- Madrahimov, Sherzod,Mostafa, Adel,Yempally, Veeranna,Fadlallah, Joelle,AlQaradawi, Siham Y.
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- Reactivity Variation of Tetracyanoethylene and 4-Phenyl-1,2,4-Triazoline-3,5-Dione in Cycloaddition Reactions in Solutions
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The reasons for the very high reactivity and variability of reactivity of two dienophiles, tetracyanoethylene (1) and 4-phenyl-1,2,4-triazoline-3,5-dione (2), in the Diels–Alder reactions were considered. The data on the rate of reactions with anthracene (3), benzanthracene (4) and dibenzanthracene (5) in 14 solvents over a range of temperatures and high pressures, data on the change in the enthalpy of solvation of reagents, transition state, and adducts in the forward and backward reactions, and the enthalpies of these reactions in solution were obtained. Strong π-acceptor dienophile 1 has sharply reduced reactivity in reactions in π-donor aromatic solvents. It was observed that the π-acceptor properties of dienophile 1 disappear upon passage to the transition state and adduct. Large solvent effects on the reaction rate can be predicted for all types of reactions involving tetracyanoethylene. Very high reactivity of dienophiles 1 and, especially, 2 can be useful to catch such carcinogenic impurities such as 3–5 and neutralize them by transformation into less dangerous adducts.
- Kiselev, Vladimir D.,Kornilov, Dmitry A.,Anikin, Oleg V.,Shulyatiev, Alexey A.,Konovalov, Alexander I.
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- Spectroscopic and thermal investigations on the charge transfer interaction between risperidone as a schizophrenia drug with some traditional π-acceptors: Part 2
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The focus of present investigation was to assess the utility of non-expensive techniques in the evaluation of risperidone (Ris) in solid and solution states with different traditional π-acceptors and subsequent incorporation of the analytical determination into pharmaceutical formulation for a faster release of risperidone. Charge-transfer complexes (CTC) of risperidone with picric acid (PA), 2,3-dichloro-5,6-dicyano-p-benzoquinon (DDQ), tetracyanoquinodimethane (TCNQ), tetracyano ethylene (TCNE), tetrabromo-p-quinon (BL) and tetrachloro-p-quinon (CL) have been studied spectrophotometrically in absolute methanol at room temperature. The stoichiometries of the complexes were found to be 1:1 ratio by the photometric molar ratio between risperidone and the π-acceptors. The equilibrium constants, molar extinction coefficient (εCT) and spectroscopic-physical parameters (standard free energy (ΔGo), oscillator strength (f), transition dipole moment (μ), resonance energy (RN) and ionization potential (ID)) of the complexes were determined upon the modified Benesi-Hildebrand equation. Risperidone in pure form was applied in this study. The results indicate that the formation constants for the complexes depend on the nature of electron acceptors and donor, and also the spectral studies of the complexes were determined by (infrared, Raman, and 1H NMR) spectra and X-ray powder diffraction (XRD). The most stable mono-protonated form of Ris is characterized by the formation of +NH (pyrimidine ring) intramolecular hydrogen bonded. In the high-wavenumber spectral region ～3400 cm-1, the bands of the +NH stretching vibrations and of the pyrimidine nitrogen atom could be potentially useful to discriminate the investigated forms of Ris. The infrared spectra of both Ris complexes are confirming the participation of +NH pyrimidine ring in the donor-acceptor interaction.
- El-Habeeb, Abeer A.,Al-Saif, Foziah A.,Refat, Moamen S.
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p. 464 - 477
(2013/04/23)
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- Why can the activation volume of the cycloadduct decomposition in isopolar retro-diels-alder reactions be negative?
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Rate constants of the Diels-Alder cycloaddition reaction of anthracene with tetracyanoethylene, enthalpy of solution of reactants and adduct, enthalpy of the reaction in solution, enthalpy and entropy of activation of the forward and retro-Diels-Alder reactions were determined in 14 solvents. Temperature and pressure effects on the rate of the decomposition of the adduct formed from 9-chloroanthracene and tetracyanoethylene were studied. Since the electrostriction effect can be excluded from the consideration of the isopolar Diels-Alder reaction, negative values of the activation volume in the retro-Diels-Alder reactions can be caused by the different possibilities of penetration of the solvent molecules to large steric branched structures of the transition states and adducts.
- Kiselev, Vladimir D.
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experimental part
p. 117 - 125
(2011/05/19)
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- One-pot new synthetic method for 3-amino-2-quinoxalinecarbonitrile
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A new method for the preparation of 3-amino-2-quinoxalinecarbonitrile (1) was studied. A successful condensation reaction between bromomalononitrile and o-phenylenediamine in the presence of Lewis acid catalyst (AlCl3) was achieved to produce compound 1.
- Waly, Mohamed Attia,El-Gogary, Sameh Ramadan,El-Sepelgy, Osama Zakaria
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scheme or table
p. 739 - 743
(2011/03/19)
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- Chemical reactivity of 3-hydrazino-5,6-diphenyl-1,2,4-triazine towards π-acceptors activated carbonitriles
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Behaviour of 3-hydrazino-5,6-diphenyl-1,2,4-triazine 1 as electron donor towards different electron acceptors activated carbonitriles has been investigated and a novel fused heterocyclic system and 2,3-disubstituted 1,2,4-triazines have been obtained. Compound 1 reacts with 1,2-dicyanobenzene as π-acceptor in DMF to form benzencarboximidamide 16, while reaction of 1 with a-bromomalononitrile 17 in boiling DMF affords compound 18. On the other hand, compound 1 reacts with tetracyanoethane 23 in DMF to yield compound 24. The route of reaction in DMF indicates that charge-transfer complexation is the key intermediate to obtain new heterocyclic systems. Structures of the products are established by MS, IR, UV-Vis, CHN and 1H NMR spectral data.
- Abdel-Rahman,Abdel-Monem
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p. 838 - 846
(2008/09/18)
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- Continuum of outer- and inner-sphere mechanisms for organic electron transfer. Steric modulation of the precursor complex in paramagnetic (ion-radical) self-exchanges
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Transient 1:1 precursor complexes for intermolecular self-exchange between various organic electron donors (D) and their paramagnetic cation radicals (D+.), as well as between different electron acceptors (A) paired with their anion radicals (A .), are spectrally (UV-NIR) observed and structurally (X-ray) identified as the cofacial (π-stacked) associates [D, D+.] and [A-.· A], respectively. Mulliken-Hush (two-state) analysis of their diagnostic intervalence bands affords the electronic coupling elements (HOA), which together with the Marcus reorganization energies (λ) from the NIR spectral data are confirmed by molecular-orbital computations. The HDA values are found to be a sensitive function of the bulky substituents surrounding the redox centers. As a result, the steric modulation of the donor/acceptor separation (rDA) leads to distinctive electron-transfer rates between sterically hindered donors/acceptors and their more open (unsubstituted) parents. The latter is discussed in the context of a continuous series of outer- and inner-sphere mechanisms for organic electron-transfer processes in a manner originally formulated by Taube and co-workers for inorganic (coordination) donor/acceptor dyads-with conciliatory attention paid to traditional organic versus inorganic concepts.
- Rosokha, Sergiy V.,Kochi, Jay K.
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p. 3683 - 3697
(2008/01/01)
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- Synthesis and reactions of the first cyclopentadienyl isonitriles
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6-Azidofulvenes without a further substituent in the exocyclic position were transformed into new 1-isocyano- and 2-isocyanocyclopenta-1,3-dienes by photolysis in methanol. These novel functionalized cyclopentadienes are useful building blocks, e.g. as dienes in Diels-Alder reactions.
- Banert, Klaus,K?hler, Frank,Meier, Barbara
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p. 3781 - 3783
(2007/10/03)
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- Reaction of 2,2-bis(trifluoromethyl)-1,1-dicyanoethylene with 6,6-dimethylfulvene: Cycloadditions and a rearrangement
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Reaction of 2,2-bis(trifluoromethyl)-1,1-dicyanoethylene (BTF;1) with 6,6-dimethylfulvene (2) affords the expected Diels-Alder cycloadduct, 7-(1-methylethylidene)-3,3-bis(trifluoromethyl)bicyclo[2.2.1]- hept-5-ene-2,2-dicarbonitrile (3), in good yield. The cycloadduct 3 is unstable and exists in equilibrium with the starting materials in less polar solvents. In more polar environment, the [4 + 2] adduct 3 either reverts to starting materials, or, in a competing process, is converted to the formal [2 + 2] adduct, 2-(1-methylethylidene)-7,7- bis(trifluoromethyl)bicyclo[3.2.0]hept-3-ene-6,6-dicarbonitrile (6). In the presence of acid, 3 is converted to a third isomeric form, 1,3a,5,6-tetrahydro- 7-methyl-5,5-bis(trifluoromethyl)-4H-indene-4,4-dicarbonitrile (8). Both 6 and 8 are formed with complete regiospecificity. Quantum mechanical calculations and X-ray crystallographic studies of this ensemble of reactions by BTF, and the analogous set of reactions by its progenitor, tetracyanoethylene (TCNE), reveal several interesting facets. The conversion of 3 to 6 occurs in certain polar solvents, in the presence of silica gel and alumina, as well as in the solid state. Single crystals of 3 were observed by X-ray crystallography to undergo crystal-to-crystal rearrangement to 6. The conversion of 3 to 8 proceeds by the initial retro-Diels -Alder reaction followed by isomerization of the fulvene to 1-isopropenyl-1,3-cyclopentadiene that then reacts with BTF to give the alternative Diels-Alder product as a single regioisomer. A hybrid density functional theory (DFT) method at the B3LYP/6-31G(d) level of theory gave calculated relative energies of 0.0, -9.0, and -18.8 kcal/mol for 3, 6, and 8, respectively. The same method was also used to correctly predict the regiochemical outcome of the cycloaddition of BTF with 1-isopropenyl-1,3-cyclopentadiene. Finally, an explanation is offered for the preference of the persubstituted cyanoolefins BTF and TCNE to add to the exocyclic diene portion of 1-isopropenyl-1,3-cyclopentadiene and the contrasting preference of 2-acetyloxy-2-propenenitrile to add to the endocyclic diene.
- Howard, Michael H.,Alexander,Marshall, William J.,Roe, D. Christopher,Zheng
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p. 120 - 129
(2007/10/03)
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- Ring contraction of 1,2-digermacyclohexa-3,5-dienes initiated by electron transfer reactions with TCNE
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The thermal reaction of 1,2-digermacyclohexa-3,5-dienes with tetracyanoethylene (TCNE) gave 1-germacyclopenta-2,4-diene as a germylene extrusion compound through a charge-transfer complex. The 1-germacyclopenta-2,4-diene was trapped with TCNE to give 5,5,6,6-tetracyano-7-germanor-bornene.
- Mochida, Kunio,Shimizu, Hiromi,Nanjo, Masato
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p. 1226 - 1227
(2007/10/03)
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- The influence of cations complexed by crown ethers on anthracene charge-transfer interactions
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Formation of organic charge-transfer complexes of two anthracene derivatives with tetracyanoethylene (TCNE) was monitored by spectroscopic methods. Both compounds form complexes with TCNE, which are exothermic and enthalpy driven. For compound 3 and TCNE, the association constant is K = 395 M-1. The presence of crown ether rings in compound 5 diminishes the association constant to K = 290 M-1. Additional complexation of potassium cation decreases the charge-transfer (CT) association to K = 142 M-1. This effect is not influenced by the second potassium cation. It is evident from NMR data that TCNE acceptor molecule is rocking over anthracene and incorporation of crown ether rings into anthracene structure slows down the kinetics of formation of the CT complex. Additional complexation of potassium cation by crown ether rings present in anthracene 5 causes a further decrease of the complexation kinetics. The overlap of donor and acceptor molecules according to X-ray data was complemented by the observation that the kinetics of complex formation is strongly dependent on the substituent present in the donor anthracene molecule.
- Ostaszewski,Kozbial
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p. 1489 - 1502
(2007/10/03)
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- Regiocontrol of Diels-Alder reaction of conjugate 1-trienol ether in chiral tropilidene with TCNE
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The Diels-Alder reaction of tetracyanoethylene (TCNE) with a 1-trienol unit in the tropilidenes at the 1,4-position was a quick and reversible process, whereas the 3,6-addition only proceeded in polar solvent and was irreversible.
- Sugimura, Takashi,Nagano, Shinya,Kohno, Harumi,Fujita, Morifumi,Tai, Akira
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p. 179 - 180
(2007/10/03)
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- Pressure effect on the rate and equilibrium constants of the Diels- Alder reaction 9-chloroanthracene with tetracyanoethylene
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The pressure effect on the forward and backward rate constants and equilibrium constants of the Diels-Alder reaction of 9-chloroanthracene with tetracyanoethylene has been investigated in 1,2-dichloroethane up to 1000 kgcm-2 at 298.15 K. The reaction volume obtained from the pressure effect on equilibrium (-20.6 ±1.5 cm3 mol-1) and as difference of activation volumes of forward (-28.5±1.5) and backward (-6.5 ± 0.5) reaction (- 22.0±1.5 cm3 mol-1) are in agreement with partial molar volume difference of adduct (255.5±1.5) {diene (170.7±0.5) and dienophile (107.8±0.2)} giving -23.0 ±2 cm3 mol-1.
- Kiselev, Vladimir D.,Kashaeva, Elena A.,Konovalov, Alexander I.
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p. 1153 - 1162
(2007/10/03)
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- Reactions at Elevated Pressures. II. Effect of Pressure on the Rate of Decomposition of the Diels-Alder Adduct of Tetracyanoethylene and 9-Chloroanthracene
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The kinetics of decomposition of the adduct of tetracyanoethylene with 9-chloroanthracene in 1,2-dichloroethane at 298 K was studied in the pressure range 0-950 atm. The calculated activation volume of the reaction is -6.5±0.5 cm3 mol-1.
- Kiselev,Kashaeva,Dmitriev,Konovalov
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p. 1616 - 1620
(2007/10/03)
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- Molecular Complexation and Kinetics for Diels-Alder Condensation of Naphthylalkenes with Tetracyanoethylene
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The charge-transfer spectra of 1:1 molecular complexes of seven 1-alkyl-1-(2-naphthyl)ethenes (where R=alkyl group: H,Me,Et,n-Pr,i-Pr,t-Bu,Neopent) and 1-vinylnaphthalene with TCNE were determined in ClCH2CH2Cl as solvent at 27.1 deg C.Equilibrium constants, K; for these complexes vary with R, as based on two opposing factors, viz. (a) the polar substituent factor ?* and (b) the angle-of-twist θ between the planes of the naphthyl and vinyl groups.For R=Neopent (?* dominant) K is 50 times as large as for R=t-Bu (θ dominant).Except for R=t-Bu, kinetics of reaction conform with the equation D+TCNE (K) D*TCNE (k1/k-1) P, where D is the donor alkene, P is the Diels-Alder 1,4-cycloaddition product, and k1 and k-1 are first-order reaction rate constants.Values of k1 vary from 0.71 min-1 (R=H) to 55.5 min-1 (R=Neopent) and the corresponding relative second-order rate constants k2 (or k1K) from 1 to 4000.The rate constant k-1 was measured only for 1b (R=Me, 0.0017 min-1) in the solvent mixture p-xylene/ClCH2CH2Cl.Formation of 1b*TCNE complex gives ΔH = 10.0 kcal/mol and ΔS = 38.4 eu, and conversion to P shows an Arrhenius activation energy of Ea = 7.24 kcal/mol.It is proposed that the preferred conformation of a naphthylalkene for complexation has the R and vinyl groups projecting outward from opposite sides of the plane of the naphthalene ring.The TCNE molecule then aligns parallel to the naphthalene ring on the vinyl side where (except for R=t-Bu) it can slide into the geometry of the transition state to form P.
- Klemm, LeRoy H.,Solomon, Wayne C.,Tamiz, Amir P.
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p. 6503 - 6510
(2007/10/03)
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- Charge-Transfer Complexes of Benzo[b]thiophene with σ- And π-Electron Acceptors
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The spectrophotometric properties of the charge-transfer (CT) complexes of benzo[6]thiophene with iodine at 24°C in different solvents such as cychlohexane, carbon tetrachloride, chloroform, dichloromethane, and 1,2-dichloroethane are studied. In addition the spectrophotometric and thermodynamic properties of the CT complexes of benzo[b]thiophene with tetracyanoethylene, chloranil, 2,3-dichloro-5,6-dicyano-p-benzoquinone and 7,7,8,8,-tetracyanoquinodimethane are studied. The results show that the equilibrium and the thermodynamic parameters and the wavelengths of the maximum absorption bands (λmax) of the complexes vary markedly with the solvent. The ionization potential and the donor sites of benzo[b]thiophene are also determined and discussed.
- Ayad, Mohamad M.
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p. 2369 - 2373
(2007/10/03)
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- A study on electronic interaction two systems connected with a C=C bond: Preparation, and of (E)-and(2)-8,8′-(Ethene-l,2-diyl)bis(5-terf-butyl[2.2]metacyclophane)
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(E)-8,8′-(Ethene-1,2-diyl)bis(5-tert-butyl]2.2]metacyclophane) (2) was obtained from a McMurry reaction of 5-tert-butyl-8-formyl[2.2jmetacyclophane (1). Irradiation of 2 with a high-pressure mercury lamp gave the corresponding (Z) isomer 3. X-ray crystallographic analyses of 2 and 3 show a certain degree of twisting of the bond connecting the metacyclophane unit and the central n system due to steric crowding. UV spectra of 2 and 3 and of the charge-transfer complexes [2/TCNE] and [3/TCNE] allow for a discussion of n-n interaction between the centrai stilbene subunit and the outer benzene rings of the metacyclophane units. Bis[2.2]metacyclophanes 2 and 3 reacted regioselectively with hexacarbonylchromiurn on the outer benzene rings giving 1:1 and 1:2 complexes 9-14 with tricarbonylchromium. No 1:3 and 1:4 complexes formed due to steric restrictions. Analysis of UV spectral data of the complexed [2.2]metacyclophanes was performed for an indication of π-π interactions in the complexes. VCH Veriagsgesellschiifi mbH, 1996.
- Ishi-i, Tsutomu,Sawada, Tsuyoshi,Mataka, Shuntaro,Tashiro, Masashi,Thiemann, Thies
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p. 289 - 296
(2007/10/02)
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- Application of Time-Dependent Raman Theory to Raman Excitation Profiles of Hexamethylbenzene-Tetracyanoethylene Electron Donor-Acceptor Complex
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Raman excitation and absorption profiles were obtained for the 1:1 electron donor-acceptor complex of hexamethylbenzene with tetracyanoethylene in dichloromethane solution.The absorption and Raman profiles were analyzed using the time-dependent theory of Heller to obtain the displacements and non-Condon factors for the four strongest Raman modes, the electronic excitation energy, the transition dipole, and solvent linebroadening parameters.The results are compared to the data reported by Myers et al (J.Am.Chem.Soc. 1992, 114, 6208) for the same complex in carbon tetrachloride solution.Attempts to account for solvent effects on the normal-mode displacements in terms of the solvent local field lead are complicated by the effect of the solvent on the structure of the complex.We propose that in CH2Cl2 but not in CCl4, the complex adopts a low-symmetry ground-state geometry which permits vibronic coupling of the charge-transfer and locally excited (TCNE) states.
- Britt, B.Mark,McHale, Jeanne L.,Friedrich, Donald M.
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p. 6347 - 6355
(2007/10/02)
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- Cycloreversion of Arene Endoperoxides induced by Electron Transfer
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Cycloreversion of arene endoperoxides 1-4 can be induced by photoexcitation of their electron donor-acceptor complexes with tetracyanoethylene.
- Takahashi, Yasutake,Morishima, Shin-ichi,Wakamatsu, Kan,Suzuki, Takanori,Miyashi, Tsutomu
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- Photoinduced Electron Transfer from Triplet Fullerene, 3C60, to Tetracyanoethylene. Fourier Transform Electron Paramagnetic Resonance Study
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Fourier transform EPR spectroscopy was employed in studying the electron transfer (ET) and the quenching mechanisms of the photoexcited triplet state of C60 (electron donor) in the presence of the electron acceptor tetracyanoethylene (TCNE) in a benzonitrile solution.The ET reaction product, which is the stable anion radical TCNE, interacts with 3C60 (both detected by EPR in the liquid phase), leading to chemically induced dynamic electron polarization of TCNE, via triplet-doublet mixing mechanism.
- Michaeli, S.,Meiklyar, V.,Schulz, M.,Moebius, K.,Levanon, H.
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p. 7444 - 7447
(2007/10/02)
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- Interactions between substituted thioureas and π-acceptors
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Charge-transfer (CT) interactions between some N-aryl-N'-heterocyclic thioureas and both tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) were investigated spectroscopically. The formed CT complexes and the solvent effect on CT complexation are discussed. N-Aryl-N'-(2-pyridyl)-thioureas 1 a-d reacted with TCNE to give cyanothiourea derivatives 6, however in case of DDQ, the adducts 7 were obtained.
- Mohamed,Hassan,Ibrahim,Semida,Mourad
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p. 592 - 595
(2007/10/02)
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- Free Energy Dependence of the Intrinsic Rate of Electron Transfer in Diffusional Quenching of trans-Stilbene S1 by Electron-Deficient Olefins
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The quenching of the first excited singlet states of trans-stilbene and 4,4'-dimethyl-trans-stilbene by acrylonitrile, fumaronitrile, and tetracyanoethylene has been examined by picosecond laser spectroscopy.The intrinsic rate constant of electron transfer is separated from the diffusion rate constant by applying the Collins and Kimball formalism for time-dependent rate constants.The intrinsic rates of electron transfer are correlated with the free energy changes for electron transfer, and it is found that the correlation does not follow the predictions of Marcus' adiabatic electron-transfer theory.
- Angel, Stephen A.,Peters, Kevin S.
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p. 3606 - 3612
(2007/10/02)
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- KINETIC AND THERMOCHEMICAL INVESTIGATION OF THE FORWARD AND REVERSE DIELS-ALDER REACTIONS OF TETRACYANOETHYLENE WITH ANTHRACENE AND 9,10-DIMETHYLANTHRACENE IN CERTAIN SOLVENTS
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The Diels-Alder reaction of tetracyanoethylene with anthracene and 9,10-dimethylanthracene was studied in the forward and reverse directions in a series of solvents.The rate constants, enthalpies and entropies of activation, enthalpies of solution of the reagents and adducts, and enthalpies of the reaction were determined.The changes in the enthalpy of solvation of the reagents, the products, and the transition state for the forward and reverse processes were calculated from the obtained data.The equality of the enthalpies of the reaction obtained from the thermochemical (ΔHr) and kinetic (ΔH1-ΔH-1) measurements suggests that the energies of intermolecular stabilization in the transition state for the forward and reverse Diels-Alder reactions are equal.The indentical changes in the enthalpy of solvation of the transition state for the forward and reverse reactions are consistent with its equilibrium solvation.
- Kiselev, V. D.,Malkov, V. B.,Konovalov, A. I.
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p. 191 - 200
(2007/10/02)
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- Photochemical generation of radical cations from α-terthienyl and related thiophenes: Kinetic behavior and magnetic field effects on radical-ion pairs in micellar solution
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The photochemistry of α-terthienyl (αT) and related compounds has been examined in homogeneous solution and in anionic micelles in the presence of electron acceptors. The absorption spectra of the radical cations from four thiophenic substrates have been characterized; for example, those derived from α-bithienyl (αB) and αT show absorption maxima at 420 and 530 nm, respectively. Triplet quenching by acceptors such as methyl viologen (MV2+) and tetracyanoethylene approaches diffusion control (k > 5 × 109 M-1 s-1). Quenching by oxygen, which is known to be dominated by singlet oxygen sensitization, involves electron transfer only to a minor extent; the highest efficiency, for αB, was only 6%. In micellar systems the behavior of the radical-ion pairs produced via electron transfer involves the competition of geminate and exit processes which occurs in the 10-7-10-6 s time domain. Both processes are slower in the larger micelles. Geminate processes are dramatically affected by magnetic fields. A model is proposed where the rate of geminate processes is suggested to depend upon the intramicellar reencounter frequency for the pair and the degree of singlet character in the triplet-derived radical-ion pair. The magnetic field effects observed are consistent with such a model.
- Evans, Christopher H.,Scaiano
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p. 2694 - 2701
(2007/10/02)
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- 7. Tetrazinodiheteroarene: 'Charge -Transfer'-Komplexbildung mit Akzeptorverbindungen
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The formation of charge-transfer complexes and radical-ion pairs of donor compounds 1-6 with acceptor compounds 7-12 has been investigated by means of VIS/NIR-spectrospcopic methods.The equilibrium constants KCT (up to 1100M-1) for the donor/acceptor couple dipyridotetrazine (2)/ethylenetetracarbonitrile (11) and spectra of the CT complexes have been determined in 1,2-dichloroethane solution at 25 deg C.Results are discussed in relation to known CT-complex properties and to voltammetric redox-potentials E1/2.
- Hellrung, Bruno,Balli, Heinz
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- Gas-phase ligand substitution reactions with the 17-electron transition-metal complexes (OC)4Fe.-, (OC)5Cr.-, and (OC)4MnH.-
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Three transition-metal complex negative ions, (OC)4Fe.-, (OC)5Cr.-, and (OC)4MnH.-, were generated and studied in ligand substitution reactions with a variety of neutral ligand substrates. Only (OC)4Fe.- reacted with PF3 and gave sequentially the product ions (OC)4-xFe(PF3)x.- where x = 1-3. The three metal complex negative ions formed ligand substitution product anions with NO; the reaction with (OC)4MnH.- also produced some of the corresponding adduct anion. With SO2, (OC)4Fe.- gave only ligand substitution, (OC)5Cr.- formed a mixture of the adduct and the product of ligand substitution, and (OC)4MnH.- produced only the adduct. Both the NO and SO2 reactions were believed to occur by the associative mechanism with the SO2 reactions proceeding via Lewis acid-base complexes. Only (NC)2C=C(CN)2 (TCNE) of the seven olefins examined reacted with the metal complex negative ions forming the product of electron transfer (TCNE.-) as well as the product ions of ligand substitution. The reactions of all three metal complex negative ions with (CF3)2C=O and of (OC)5Cr.- with biacetyl were considered to involve initial electron transfer within the orbiting collision complex. The reaction of (OC)4MnH.- with O2 produced various oxidation products, the most noteworthy being HCO2- as a major product anion. This latter result is considered to be evidence for the migratory insertion reaction, OC-Mn-H ? Mn-CHO, in the adduct formed from (OC)4MnH.- with O2.
- McDonald, Richard N.,Schell, Philip L.
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p. 1820 - 1827
(2008/10/08)
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- Gas-phase ligand substitution reactions with (OC)Fe(NO)2.-', (OC)2Co(NO).-, (η3-C3H5)Co(CO)2.-, (C3H5)Co(CO)3.-, and CpCo(CO)2.-
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Three 17-electron transition-metal complex negative ions LM(CO)x-1.- ((OC)Fe(NO)2.-, (OC)2Co(NO).-, and (η3-C3H5)Co(CO)2.-) and two parent molecular anion radicals LM(CO)x.- ((C3H5)Co(CO)3.- and CpCo(CO)2.-) were generated by electron impact on the corresponding LM(CO)x complexes in the gas phase. The ion-molecule reactions of these five metal complex negative ions were studied with the neutral molecules PF3, PMe3, NO, SO2, olefins with electron-donating and -withdrawing vinyl substituents, acetone and certain fluorinated derivatives, biacetyl, O2, CO, and CS2. In general, the LM(CO)x-1.- complexes and CpCo(CO)2.- reacted by ligand substitution involving the associative mechanism. In many cases, the product ions of adduct formation and ligand substitution were directly observed in the same reaction. These ligand substitution reactions appear to take advantage of the abbility of the NO, η3-C3H5, and Cp ligands to reduce their hapticities as the neutral ligand bonds to the metal. The reaction of (C3H5)Co(CO)3.- with PF3 occurred by fragmentation of the allyl radical. This latter result was considered to occur by radical β-fragmentation of the excited acyl complex [C3H5C(=O)Co(CO)2(PF3) .-]* formed by CO insertion into the Co-allyl bond. Both parent molecular anion radicals were observed to undergo electron transfer with several of the neutral substrates yielding EA((η3-C3H5)Co(CO)3) = EA(CpCo(CO)2) = 0.62 ± 0.1 eV; EA(η3-C3H5)Co(CO)2) = 0.9 ± 0.2 eV was also measured. The results of the reactions of the parent LM(CO)x.- species with the neutral ligands were consistent with their structures having a 17-electron configuration about the metal with η3-Cp and η1-C3H5 ligands.
- McDonald, Richard N.,Schell, Philip L.
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p. 1806 - 1820
(2008/10/08)
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- Charge-Transfer Complexes and Reactivity in Diels-Alder Cycloadditions
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The reactivity of 2,3-bis(methylene)norbornane (1) towards the highly reactive dienophiles 2,3-dicyano-p-benzoquinone (2), tetracyanoethylene (3), 2,3-dicyanomaleimide (4), and p-benzoquinone-2,3-dicarboxyclic anhydride (5) was analysed kinetically.CT complexes were observed for 1 with 2-5 and equilibrium constants for the formation of the CT complexes between 1 and 2-4 were determined kinetically.The relationship between relative rates, CT-excitation energies, HOMO-LUMO separations, and CT-complex equilibrium constants is discussed.The results do not require the CT complexes to be intermediates but strongly support the importance of CT interactions in the transition state of these cycloadditions.
- Sustmann, Reiner,Dern, Mechthild,Kasten, Ronald,Sicking, Willi
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p. 1315 - 1322
(2007/10/02)
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- PHOTOCHEMISTRY OF BRIDGED CYCLOHEPTADIENES. MULTIPLICITY DEPENDENT PERICYCLIC REARRENGEMENTS OF EXCITED BICYCLONONA-2,4-DIENE-7,7,8,8-TETRACARBONITRILE
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Bicyclonona-2,4-diene-7,7,8,8-tetracarbonitrile rearranges selectively under direct irradiation in acetonitrile to tricyclo2,4>non-6-ene-8,8,9,9-tetracarbonitrile, and upon acetone sensitization to bicyclonona-2,6-diene-8,8,9,9-tetracarbonitrile.Both products are derived from sigma bond cleavage, in contrast to the parent unsubstituted diene where only the ?-bonds react.
- Goldschmidt, Zeev,Genizi, Elisheva
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p. 4867 - 4870
(2007/10/02)
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- GENERATION AND DIENOPHILIC REACTIVITY OF α-OXOSELENOALDEHYDES AND KETONES
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The reaction elemental selenium with sulfur ylides stabilized by electron-withdrawing substituent(s) affords a facile method for generation of functionalized selenocarbonyl compounds, which can be effectively trapped by Diels-Alder reaction with 1,3-dienes.
- Nakayama, Juzo,Akimoto, Keiichi,Niijima, Jun,Hoshino, Masamatsu
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p. 4423 - 4426
(2007/10/02)
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- Electron Affinities of Di- and Tetracyanoethylene and Cyanobenzenes Based on Measurements of Gas-Phase Electron-Transfer Equilibria
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The electron affinities of tetracyanoethylene, trans-1,2-dicyanoethylene, and eleven substituted benzonitriles as well as two naphthonitriles were determined by measurement of the electron-transfer equilibria A-+B=A+B- with a pulsed electron high ion source pressure mass spectrometer.Rate constants for exothermic electron transfer involving the cyano compounds were found to be near unit collision efficiency.The EA (tetracyanoethylene)=3.17 eV obtained in the present work is considerably higher than the 2.3 eV photodetachment value of Palmer and Lyons.The electron affinities of benzene and benzonitrile substituted by CN, CHO, and NO2 increase in the given order, while the order for nitrobenzene is CHO, CN, NO2.This reversal of order is explained on the basis of a larger attenuation of the ?-withdrawing effect relative to the field effect of substituents when the electron density in the ?* single-electron orbital is decreased.
- Chowdhury, Swapan,Kebarle, Paul
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p. 5453 - 5459
(2007/10/02)
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- MESOIONIC THIOCARBONYL YLIDES
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Four kinds of mesoionic thiocarbonyl ylides were synthesized by the treatment of mesoionic thiolate with bromine followed by the reaction with conjugate base of active methylene compounds.The structures were discussed based on the spectroscopic properties.
- Araki, Shuki,Butsugan, Yasuo
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p. 1639 - 1642
(2007/10/02)
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- STUDIES OF THE CHARGE-TRANSPHER COMPLEXES OF AZOXY COMPOUNDS WITH ?-ACCEPTORS
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Charge-transfer complexes of aryl azoxy compounds with some ?-acceptors in dichloromethane were studied spectrophotometrically at 25 deg C in the visible region.The spectroscopic data indicate that the complexes are not strong in nature and the Ph-N=-->O group is resposible for the complexation with ?-acceptors.Comparison with nitrones has been made.The 1H NMR and IR spectra of some solid complexes differ in important respects from those of either component taken separately.The effect of temperature on the stability of the complexes is discussed.Job's method shows that the stoicheiometric ratio of the complexes is 1:1.
- El-Din, Ahmed Moukhtar Nour
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p. 401 - 404
(2007/10/02)
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- ?-? Molecular Complexes with Nitrones: PartIV - Substituent Effect in the Complexation of Aryl Nitrones with Tetracyanoethylene and 1,4-Benzoquinones
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Charge-transfer complexes of some substituted nitrones with tetracyanoethylene and 1,4-benzoquinones have been studied spectrophotometrically.The stoichiometry and apparent formation constants of the complexes have been determined.From the energies of the charge-transfer transitions, the ionization potentials of the donors have been obtained.
- Nour El-Din, Ahmed M.
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p. 511 - 512
(2007/10/02)
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- Optical and Resonance Raman Studies of the 1:1 and 2:1 Complexes of Hexamethylbenzene with Tetracyanoethylene
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The electron donor-acceptor (EDA) complexes of hexamethylbenzene (HMB) and tetracyanoethylene (TCNE) have been studied by optical and resonance Raman spectroscopy in a variety of solvents.The visible absorption spectra of the 1:1 and 2:1 complexes in cyclohexane have been resolved by multiwavelength linear regression of concentration-dependent absorbance data. the resonance Raman spectra of CCl4, CH2Cl2, and cyclohexane solutions of HMB and TCNE have been obtained with 5145-Angstroem excitation.A low-frequency mode at 163-169 cm-1 is assigned to the first overtone of the donor-acceptor stretch, νDA.In cyclohexane, the second overtone of νDA is also observed, but is overlapped by an a2u out-of-plane bending vibration of the methyl groups of HMB, which becomes allowed in the 2:1 complex due to vibronic coupling.A simple molecular orbital picture of the bonding in the 1:1 and 2:1 complexes is proposed which explains the resolved visible spectra as well as the low-frequency Raman data.It is concluded that the second donor molecule is not bound by "charge-transfer" forces, and that, although the ground state 2:1 complex has D2h symmerty, the two D-A bonds are of unequal strngth.
- Smith, Morgan L.,McHale, Jeanne L.
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p. 4002 - 4007
(2007/10/02)
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- Reaktion von trans-1-Arylbutadienen und 1,1-Diarylbutadienen mit Tetracyanethylen (TCNE) und 2,2-Bis(trifluormethyl)ethylen-1,1-dicarbonitril (BTF): Kinetische Studie
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Kinetic data (substituent effects, solvent effects, activation parameter) are reported for the reactions of trans-1-arylbutadienes 1 and 1,1-diarylbutadienes 3 with TCNE 4 and BTF 5. (2+2)- and (4+2)-cycloadducts 7 respectively 9 can rearrange or undergo cycloreversions with quite different reaction rates depending on the substituent in the aryl-ring.
- Drexler, J.,Lindermayer, R.,Hassan, M. A.,Sauer, J.
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p. 2559 - 2562
(2007/10/02)
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- ELECTRON-DONATING PROPERTIES OF SOME N-ARYLPYRROOLES. I. CHARGE-TRANSFER COMPLEXES
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The complex formation between some N-arylpyrroles and the electron acceptors iodine, tetracyanoethylene, and chloranil has been investigated spectrophotometrically.Association constants, free energies of formation and other thermodynamic properties have been calculated for the charge-transfer complexes of these systems.Values of band maxima were used to calculate the ionisation potentials of the donors.Factors governing the stability of the molecular complexes studied are analysed and discussed.
- Abu-Eittah, Rafie H.,Hilal, Refat H.,El-Shall, Mohamed S.
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p. 487 - 492
(2007/10/02)
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- On the Reaction of Chloranil with Cyanide Ions - an ESR Study
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The reaction of chloranil 1 with cyanide ions in acetonitrile and methanol solutions has been studied.The ESR spectra revealed the formation of semiquinone anion radicals 7, 8, and 9.The latter has been found as its protonated form in methanol only.In addition, both 1 and 2,3-dicyano-5,6-dichloro-1,4-benzoquinone 4 gave tetracyanoethylene anion radicals 6 upon reaction with cyanide ions in acetonitrile.Using 13C-labelled cyanide 6 was shown to originate from the fragmentation of the cyanide addition product to 4.Using the spin trapping technique it was found that no cyanyl free radicals are formed during the thermal reaction of either 1 or 4 with cyanide ions.
- Rehorek, Detlef,Janzen, Edward G.
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p. 705 - 717
(2007/10/02)
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- Role of O- Ions in Charge-Transfer Reactions at the Surface of Silica-Supported Molybdenum Catalysts Prepared by the Grafting Method
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In order to elucidate the possible order of O- ions in charge-transfer processes, the reaction of adsorbed O- ions with electron acceptor molecules has been investigated on grafted Mo/SiO2 catalysts.It is shown that their high reactivity might explain the fact that O- cannot be detected in charge-transfer reactions on oxide surfaces between acceptor molecules (A) and surface oxygen in low coordination (OLC2-) A + OLC2- -> O- + A-.Tetracyanoethylene (TCNE) readily reacts with adsorbed O- ions to form a new intermediate species (g = 2.003, doublet with aH = 50 +/- 1 G).The hyperfine splitting and experiments performed with various molecules suggest that TCNE undergoes successive reactions with adsorbed O- species and OH- surface ions to lead to the formation of an intermediate species assumed to be (CN)-CH=C.(CN) (aH is the coupling constant between the unpaired electron and the proton located trans to it on the β carbon).This species is stable at room temperature, but can react in the presence of excess TCNE and lead to the formation of TCNE- radical.The reaction between fumaronitrile H(CN)=(CN)H and adsorbed O- ions induces the same doublet with the same coupling constant and confirms the identification of the intermediate species observed with TCNE.It further indicates that the proton is more easily abstracted by O- than the CN group.This work also shows that on reduced Mo/SiO2 catalysts, the Mo5+ ions act as electron donor centers while on the oxidized catalysts, the surface O2- ions do not lead to charge-transfer reactions with TCNE.
- Che, M.,Dyrek, K.,Louis, C.
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p. 4531 - 4535
(2007/10/02)
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- Cycloreversion Induced by Charge-Transfer Excitation of Electron Donor-Acceptor Complexes. Wavelength-Dependent Photochemistry of Dianthracene
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The electron donor-acceptor or EDA complexes of dianthracene (An2 is the ?-dimer of anthracene) and its derivatives with tetracyanoethylene show two unusually well-resolved charge-transfer (CT) bands.Specific irradiation of each of these absorption bands with monochromatic light at five selected wavelengths ranging from 405 to 577 nm leads to the clean cycloreversion of An2 to anthracene.The striking wavelength-dependent quantum efficiency for cycloreversion is analyzed in terms of two different CT ion pairs derived from the photoexcitation of the first and second absorption bands, which correspond to electron promotion from the HOMO and SHOMO (second highest occupied molecular orbital) of the dianthracene donor, respectively.Orbital correlations between dianthracene ?-dimer reveal that electron promotion from the SHOMO of dianthracene leads to an excited radical ion An2(+) which is more dissociative than that derived from the HOMO transition.
- Masnovi, J. M.,Kochi, J. K.
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p. 6781 - 6788
(2007/10/02)
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- Effects of Base on Oxidation of an NADH Model Compound by Iron(III) Complexes and Tetracyanoethylene
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Effects of base on both an electron-transfer reaction from an NADH model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH) to (3+) (N-N = 2,2'-bipyridine and 1,10-phenanthroline) and a hydride transfer from BNAH to tetracyanoethylene (TCNE) in acetonitrile have been examined.The stoicheiometry of the electron transfer from BNAH to (3+) in the absence of a base indicates that BNAH is a one-electron donor.In the presence of a base, however, BNAH acts as an apparent two-electron donor, when the two-electron transfer proceeds via a multistep process; a fast one-electron transfer from BNAH to (3+) occurred, followed by the rate-determining deprotonation of BNAH+. by base and the subsequent fast electron transfer from BNA. to (3+).The rate constants for the proton transfer from BNAH+. to a series of pyridine derivatives have been determined.In the reduction of TCNE by BNAH, BNAH appears to be a two-electron donor in both the absence and presence of a base.Rates of the reduction of TCNE by BNAH increased with inceasing base concentration, suggesting the involvement of BNAH+. as an intermediate in the hydride transfer from BNAH to TCNE.The kinetic analyses have led to the evaluation of the proton transfer rate constants for the deprotonation of BNAH+. with various bases, which accord with those obtained from the electron-transfer reactions of BNAH with (3+) in the presence of bases.Based on the Broensted plot of the proton transfer rate constants as well as the variation of the primary kinetic isotope effects kH/kD with the pKa of the base, the pKa value for BNAH+. has been evaluated as 3.6 +/-0.4.
- Fukuzumi, Shunichi,Kondo, Yuji,Tanaka,Toshio
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p. 673 - 680
(2007/10/02)
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- EVIDENCE FOR A SINGLE ELECTRON TRANSFER ACTIVATION IN THE HYDRIDE TRANSFER FROM AN NADH MODEL COMPOUND TO TETRACYANOETHYLENE
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New evidence for a stepwise mechanism which requires a single electron transfer activation in the hydride transfer from an NADH model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH), to tetracyanoethylene (TCNE) has been presented based on the effects of pyridine on the stoichiometry of the overall reaction, the rate constant, and the kinetic isotope effect.
- Fukuzimi, Shunichi,Kondo, Yuji,Tanaka, Toshio
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p. 751 - 754
(2007/10/02)
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- Pressure Effect on Reaction Rate of Cycloaddition of Tetracyanoethylene with α-Methylstyrene in Some Aprotic Solvents
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The high-pressure kinetic study of the title reaction was carried out at 25 deg C up to 1500 bar in carbon tetrachloride, chloroform, 1,2-dichloroethane, and acetonitrile, taking into account the role of the EDA complex formation.The dipole moment at the transition state is as large as 8.5 +/- 0.5 debye by Kirkwood's electrostatic model.The solvent effect is also ascribable to the polarity change upon activation.The intrinsic volume of activation is -27 +/- 3 cm3/mol for the cycloadding process and -3.3 +/- 3 cm3/mol for the reverse reaction.
- Tsuzuki, Hideaki,Uosaki, Yasuhiro,Nakahara, Masaru,Sasaki, Muneo,Osugi, Jiro
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p. 1348 - 1351
(2007/10/02)
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