On the Dissociation of Aromatic Radical Anions in Solution

A new theoretical formulation is given for the reaction rate and path for the important reaction class of aromatic radical anion dissociation in solution [Ar? X]^?.→Ar^.+X^?, and is illustrated for the case of the cyanochlorobenzene radical anion [CN? Φ? Cl]^?. in dimethylformamide. Among the theory's novel features is the inclusion of the conical intersection aspect of this ground electronic state problem, which is key in allowing the reaction to occur and which has a significant impact on the reaction barrier height. Reasonable agreement with the experimental rate is found.     

Conversion of Triple Bonds into Single Bonds in a Domino Carbopalladation with Norbornene

A domino carbopalladation reaction of haloalkynes is presented. Remarkably, the four‐time carbopalladation process converts the carbon‐carbon triple bonds of haloalkynes stepwise into carbon–carbon double bonds, and finally to carbon‐carbon single bonds. Features of this reaction are that the carbon‐carbon double bonds of stable vinyl palladium intermediates are transformed into carbon‐carbon single bonds with the generation of unstable alkyl palladium intermediates. The subsequently formed π‐allylpalladium species are independently trapped by N ‐tosylhydrazones, boronic acids, and B₂pin₂ in a highly diastereoselective manner, delivering the corresponding polycyclic and twisted products with a bicyclo[3.2.1]oct‐2‐en‐3‐yl)tricyclo[3.2.1.0^2,4]octane core skeleton in moderate to good yields via C−C and C−B bond formations. Significantly, the dual roles of norbornenes, ring construction and ring expansion, and the identification of electron‐rich tri(2‐furyl)phosphine as the ligand are found to be critical for the success of these transformations.     

Aromatic Radical Anions in Neat Aromatic Hydrocarbons as Solvents. Direct evidence of through space spin-density transfer to the ligand of the counter ion

Contact ion pairs of aromatic radical anions, with a crown ether complex of potassium as cation in a neat aromatic hydrocarbon, can be obtained by reducing the aromatic hydrocarbon in which a small amount of crown ether is dissolved. The unpaired electron stays attached to one aromatic molecule during a time interval which is long on the ESR. time scale. The radicals are stabilized by ion-pair formation in the low polarity solvent. As a consequence of this stabilization, radicals of compounds with low electron affinities, e.g. mesitylene, can be prepared. Mesitylene, m-xylene, and toluene show additional hyperfine splitting in the ESR. spectra of their anion radical pairs of the order of 18 μT. The proton ENDOR. spectra have signals at the corresponding frequencies, indicating a hyperfine coupling with protons of the crown ether ligand. Using mixtures of two aromatic compounds, their relative electron affinities can be determined by studying the temperature dependence of the radical concentrations.     

Dissociation Chemistry of Hydrogen-Deficient Radical Peptide Anions

The fragmentation chemistry of anionic deprotonated hydrogen-deficient radical peptides is investigated. Homolytic photodissociation of carbon–iodine bonds with 266 nm light is used to generate the radical species, which are subsequently subjected to collisional activation to induce further dissociation. The charges do not play a central role in the fragmentation chemistry; hence deprotonated peptides that fragment via radical directed dissociation do so via mechanisms which have been reported previously for protonated peptides. However, charge polarity does influence the overall fragmentation of the peptide. For example, the absence of mobile protons favors radical directed dissociation for singly deprotonated peptides. Similarly, a favorable dissociation mechanism initiated at the N-terminus is more notable for anionic peptides where the N-terminus is not protonated (which inhibits the mechanism). In addition, collisional activation of the anionic peptides containing carbon–iodine bonds leads to homolytic cleavage and generation of the radical species, which is not observed for protonated peptides presumably due to competition from lower energy dissociation channels. Finally, for multiply deprotonated radical peptides, electron detachment becomes a competitive channel both during the initial photoactivation and following subsequent collisional activation of the radical. Possible mechanisms that might account for this novel collision-induced electron detachment are discussed.     

Out-of-Plane Distortions of Chlorinated Nitrobenzene Radical Anions

According to UHF/INDO calculations of the model conformations of the chlorinated nitrobenzene radical anions, the rotation of the nitro group relative to the plane of the benzene ring is accompanied by its pyramidal deformation caused by the pseudo-Jahn–Teller effect. The degree of the structural distortions of the chlorinated nitrobenzene radical anions depends on the arrangement of the chlorine atoms in the benzene ring and on the solvent, increasing from DMF to its mixtures with water. The isotropic hyperfine coupling constants and their dependence on the water content in a binary mixture of solvents are interpreted for a number of chlorinated nitrobenzene radical anions.     

Out-of-Plane Distortions in Fluorinated Nitrobenzene Radical Anions

According to the data of UHF/INDO calculations of the model conformations of fluorinated nitrobenzene radical anions, rotation of the nitro group relative to the plane of the benzene ring is accompanied by a pyramidal distortion of the group, which is of pseudo-Jahn–Teller nature. The degree of structural distortions depends on the position of the fluorine atoms in the benzene ring and on the solvent, increasing from DMF to DMF–water mixtures. The values of isotropic hyperfine interaction constants are interpreted in the series of fluorinated nitrobenzene radical anions, and the effects of water content in binary mixtures of solvents are discussed.     

The Radical Cations and the Radical Anions of Some Weitz-Type S-Donors

The radical cations and the radical anions of 1,6-dithiapyrene ( 1 ) and 3,10-dithiaperylene ( 2 ) as well as those of three further Weitz-type S-donors 3 , 4 , and 5 have been studied by ESR spectroscopy. The experimental findings for (widths and behaviour on saturation of hyperfine lines) suggest that the ground state of this radical anion is effectively degenerate. With the exception of , the ESR studies of all radical ions could be complemented by the use of the ENDOR and general TRIPLE resonance techniques. In addition to proton hyperfine data, ³³S coupling constants have been determined for (0.53mT), (0.46mT), and (0.34mT); they are in agreement with the predicted substantial π-spin populations at the S-atoms.     

锰催化芳香碳-氧键的还原断裂

这里发现锰化合物能够催化芳香碳-氧键的还原断裂.就我们所知,目前还没有锰催化芳香碳-氧键断裂方面的报道.以二苯并呋喃为底物,对各种反应条件进行优化,得到的较佳反应条件为5％ Mn(OAc)2,3当量Li-A1H4,140 ℃温度,四氢呋喃溶剂.在这个反应条件下,多种芳香碳-氧键能够发生还原断裂.甲醇钠的添加能够有效地促进二苯醚等底物的反应.对反应机理进行了初步研究,结果表明反应可能经历自由基过程.     

Semihydrogenaticn of Triple Bonds in 1-Alkeue Solutions

Using 1-alkenes as solvent, catalytic reduction of alkynes in the presence of Lindlar's catalyst is achieved without risking over-reduction of terminal unsaturation.     

Interaction of Aromatic Hydrocarbons with Sulfuric Acid,Bisulfate and Sulfate Anions

<正>Intermolecular geometries and energies of the dimers formed between simple aromatic hydrocarbons(benzene,toluene and naphthalene)and sulfate species(sulfuric acid, bisulfate and sulfate)were studied by density functional theory.The AH:H_2SO_4 complexes were determined by the OH-πH-bond,with H_2SO_4 acting as the H-bond donor and AHs as the acceptor. However,the AHs:HSO_4~-and AHs:SO_4~(2-)complexes were established by the H-bond,with AHs serving as acid and HSO_4~-or SO_4~(2-)as alkali.The atmospheric implications of those complexes were strongly supported by their considerable binding energies.     

The Radical Anions of Some Benzo-Derivatives of Dehydrocyclooctatetraenes

The radical anions of 5,6-didehydrobenzocyclooctene ( 3 ), 5,6,9,10-tetradehydrobenzocyclooctene ( 4 ) and 1,4,7,10-tetramethyl-5,6-didehydrodibenzo[a, e]-cyclooctene ( 6 ) were prepared in situ from dibromo-precursors and have been characterized by ESR and ENDOR spectroscopy.     

Isomerization of the Radical Anions of 6a-Thiathiophthenes

The radical anions of 6a-thiathiophthenes ([1,2]dithiolo[1,5-b] [1,2]dithioles), I(R), convert into those of 4H-thiapyran-4-thiones, III(R), via cis-trans isomerization. The reaction is slowed down when the size of the substituent R in the 2,5-positions of 6a-thiathiophthene increases, and it is prevented by the introduction of a 3,4-polymethylene bridge. The primary and the secondary radical anions, I(R)\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document} and III(R)\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}, respectively, exhibit very similar hyperfine splitting patterns. E.g., in the case of the unsubstituted 6a-thiathiophthene, I(H), and 4H-thiapyran-4-thione, III(H), the proton coupling constants are a_H2,5=6.72 and a_H3,4=1.73 Gauss for I(H)\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}, and a_H2,6=6.35 and a_H3,5=2.07 Gauss for III(H)\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}. In contrast to I(H)\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}, cis-trans isomerization could not thus far be proved to occur with its 1,6-dioxa-analogue, IV(H)\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}, since no ESR. spectrum of the radical anion of 4H-pyran-4-thione, V(H), was detected upon reduction of IV(H).     

Solvent-Free Crossed Aldol Condensation of Ketones with Aromatic Aldehydes Mediated by Magnesium Hydrogensulfate

Summary.  Crossed aldol condensations of ketones with aromatic aldehydes are carried out efficiently in the presence of magnesium hydrogensulfate under solvent-free conditions in good to excellent yield without the occurrence of any self-condensation. Similar reactions in solution do not proceed satisfactorily. Corresponding authors. E-mail: p-salehi@cc.sbu.ac.ir Received September 20, 2001. Accepted (revised) January 16, 2002     

Solvent-Free Crossed Aldol Condensation of Ketones with Aromatic Aldehydes Mediated by Magnesium Hydrogensulfate

 Crossed aldol condensations of ketones with aromatic aldehydes are carried out efficiently in the presence of magnesium hydrogensulfate under solvent-free conditions in good to excellent yield without the occurrence of any self-condensation. Similar reactions in solution do not proceed satisfactorily.     

Bimolecular Reactions of Radical Generation Involving Nitrogen-Containing Compounds with Multiple Bonds

Retrodisproportionation reactions R"C=NR" + HY R" NHR" + , RCN + HY R =NH + , RN=NR + HY R NHR + , RNO + HY R OH + , and RNO₂ + HY RN( )OH + (where HY represents hydrocarbons, alcohols, phenols, amines, thiophenols, etc.) are considered as sources of radical generation. The enthalpies of these reactions are calculated. The parabolic model is used to calculate the rate constants for 254 such reactions. Various HY compounds acting as hydrogen-atom donors are compared with nitrogen-containing compounds acting as hydrogen-atom acceptors. The PhN(O) and PhNO₂ compounds exhibit the highest activity among the studied acceptors.