Formation of the 5-Azoniafulvene Ion and its Benzo-annellated Analogue from N-Mannich Bases of Pyrrole and Indole

1-Dialkylaminomethylpyrroles are shown to behave in many respects like aminals. Acylation by an acid chloride, for instance, occurs normally at the amine-type N-atom rather than at the pyrrole ring. Spontaneous cleavage of the resulting quaternary acylammonium salts affords the 5-azoniafulvene ion ( 3 ). This higly reactive iminium ion, and its benzo-annellated analogue ( 4 ) can be trapped by electron rich aromatic compounds such as N-methylpyrrole or N,N-dimethylaniline. More elaborate N-Mannich bases are accessible by addition of indoles to enamines.     

Cyclopentadienyl(iron)arene-bis-(p-N,N-dimethylaminobenzylidene)-cyclopentanone Photoinitiated Polymerization of Methyl Methacrylate and Styrene

Abstract

Polymerization of methyl methacrylate and styrene can be effectively photoinitiated by a binary photoinitiator system consisting of cyclopentadienyl(iron)arene hexafluorophosphonate salt and bis(p-N, N-dimethylaminobenzylidene)cyclopentanone in the spectral range of 400–500 nm. The amine-type radical formed from the exciplex of the binary photoinitiator system is probably responsible for the radical polymerization of vinyl monomers. A probable mechanism of initiation of polymerization is discussed.     

Crown ether-tert-ammonium salt complex fixed as rotaxane and its derivation to nonionic rotaxane

First rotaxane having tert-ammonium axle was prepared from tert-ammonium salt axle and dibenzo-24-crown-8-ether (DB24C8) wheel, suggesting that tert-ammonium salt axle forms the corresponding threaded complex with a crown ether. Same rotaxane was obtained quantitatively by N-methylation of sec-ammonium-type rotaxane. The tert-ammonium-type rotaxane was neutralized with amine base to tert-amine-type rotaxane in 100% yield, indicating the first isolation of ‘nonionic’ amine-type rotaxane. The reversible protonation and deprotonation of tert-amine-type rotaxane were achieved.     

Participation of Non-Conjugated Double Bonds in Diels-Alder Reactions. A kinetic study of the addition of tropone to norbornens

A kinetic study of Diels-Alder additions between norbornene derivatives acting as dienophiles and the dienes tropone, perchlorocyclopentadiene and 9,10-dimethylanthracene is presented. The results suggest that tropone thereby acts as an electron acceptor, classifying these reactions then as Diels-Alder additions with ‘inverse electron demand’. The role of non-reacting double bonds was investigated using 7-alkylidenorbornene derivatives as dienophiles. These show comparable reactivity in ‘normal’ but enhanced reactivity in ‘inverse electron demand’ Diels-Alder additions. This outcome is interpreted in terms of frontier orbital interactions between the reactants using photoelectron spectroscopical results as a basis for the qualitative perturbation treatment. It is suggested that the enhanced reactivity in the case of the 7-alkylidene derivatives does not necessitate the consideration of a direct (‘through-space’) participation of the non-reacting double bond.     

Graphene-supported small-sized palladium nanoparticles made by facile photochemical approaches

To achieve small-sized and well-dispersed palladium (Pd) nanoparticles, we make use of effective photochemical approaches to synthesis of clean Pd nanoparticles on the surface of graphene at room temperature. By modulating the photochemical reaction conditions, the size and dispersion of graphene–Pd composites can be well controlled, where PdCl₄²⁻ and graphene oxide (GO) are the reaction precursors, Hantzsch 1,4-dihydropyridine (HEH) is used as an electron donor and an amine-type ligand to stabilize small Pd nanoparticles on the surface of graphene. As a result, the easy and effective photochemical approaches to the graphene–Pd composites with well-dispersed, small-sized Pd nanoparticles and highly conductive reduced GO, are established. Good to excellent yields have also been achieved with the graphene-supported Pd nanoparticles catalysts for the Suzuki coupling reaction.     

Neighbouring group participation and the tool of increasing electron demand: A review

Solvolytic reactions could be greatly influenced by the presence of neighbouring groups. The tool of increasing electron demand has been successfully used to detect such participation. For example, the tool has detected the presence of major π-participation inanti-7-norbornenyl and π-conjugation in cyclohexen-2-yl derivatives. The changes observed in the absolute values ofp ⁺ with ring size in cyclic systems could be adequately explained by the I-strain concept. The tool has established major πδ-conjugation in cyclopropylcarbinyl and nortricyclyl derivatives. πδ-participation in the Coates’ cation has been unambiguously established. However, this sensitive probe has failed to provide evidence for δ-participation in the solvolysis of 2-norbornyl system. It, is concluded that the tool of increasing electron demand is quite sensitive to detect the presence or absence or neighbouring group participation.     

Templating route for mesostructured calcium phosphates with carboxylic acid- and amine-type surfactants

Mesostructured calcium phosphates constructed by ionic frameworks were synthesized using carboxylic acid- and amine-type surfactants in mixed solvent systems of ethanol and water. A lamellar mesostructured calcium phosphate was prepared using palmitic acid as an anionic surfactant, as in the case using n-alkylamines. A wormhole-like mesostructured calcium phosphate can be obtained using dicarboxyl N-lauroyl- l-glutamic acid, whose headgroup is larger than that of palmitic acid. Similar mesostructured product was obtained using 4-dodecyldiethylenetriamine with a large headgroup containing two primary amine groups. Interactions of carboxyl and primary amino groups in the surfactant molecules with inorganic species are quite important for the formation of mesostructured calcium phosphates. The Ca/P molar ratio of mesostructured calcium phosphates was strongly affected by the molecular structure of surfactants containing carboxyl and primary amino groups. Ca-rich materials can be obtained using carboxylic acid-type surfactants (Ca/P approximately 1.7) rather than amine-type surfactants (Ca/P approximately 1.0).     

1H NMR Study of Quaternization of 2,4-Di-tert-butyl-6-dimethylaminomethylphenol

The possibility was revealed for exhaustive protonation of 2,4-di-tert-butyl-6-dimethylaminomethylphenol with participation of lone electron pairs on both nitrogen and oxygen atoms. The reaction of the title compound with alkyl halides includes concurrent and consecutive processes leading to formation of the corresponding hydrohalides and quaternization products. The latter undergo spontaneous oxidation with atmospheric oxygen to give quaternary 6,8-di-tert-butyl-3-methyl-2H-3,4-dihydro-1,3-benzoxazine derivatives which were detected by ¹H NMR spectroscopy.     

Ammoniakverlust aus α,ω-Alkandiaminen im Massenspektrometer. 22. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen

Loss of ammonia from α,ω-alkanediamines in the mass spectrometer . Under electron impact α,ω-alkanediamines lose ammonia from the molecular ion. This fragmentation reaction is explained in the case of 1.4-butanediamine ( 1 ) on the basis of the spectra of homologues and deuteriated derivatives. The reaction proceeds via neighbouring group participation; the mechanism is given in Scheme 1.     

Metal–insulator transition in the Hubbard model on a triangular lattice with disorders: Renormalization group approach

A multistages block renormalization group approach to study the metal–insulator transition in the Hubbard model on a triangular lattice with hexagonal blocks is presented and implemented. A second‐order phase transition with a critical point at U/t = 12.5 is obtained (the coupling parameters U and t correspond to the repulsive charging energy and to the nearest‐neighbor exchange coupling terms, respectively). In the presence of disorder the phase diagram for the system exhibits a metallic phase, an insulating phase, and a domain‐localized phase that separates them in the Mott regime. The subtle influence of electron–electron interactions upon inverse participation rate in the Anderson regime is also investigated. The results are discussed in light of experimental evidence for arrays of metalic quantum dots and exact numerical diagonalization of the Hubbard Hamiltonian. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 360–374, 2003     

Electron impact induced water elimination from hydroxyamides. 1—N-(2′-hydroxyethyl)piperidone-2 and N-3′-hydroxypropyl piperidone-2

The main process of the electron impact induced water elimination of the title compounds takes a reaction course comprising several individual steps. A characteristic neighbouring group participation of the carbonyl function is involved, onto which a hydrogen is transferred in a first rate-determining reaction step. This rearranged hydrogen is finally lost together with the hydroxyl group. The reaction of N-(2′-hydroxyethyl)piperidone follows what seems to be a [1,1] elimination whereas the H₂O elimination from N-(3′-hydroxypropyl)piperidone represents a formal [1,2] elimination.     

Etude de cyclohexanediols par spectrométrie de masse

Low resolution mass spectra of cyclohexane-1,2-diols and of deuterium labelled cyclohexane-1,2-diols cis and trans have been measured. The results indicate that it is easy to differentiate between positional isomers and that the stereochemistry of cyclohexane-1,2-diols can be deduced from the mass spectra. In the 1,2-diols the elimination of water under electron impact occurs simultaneously in three ways: (a) between an OH group and a H atom in position 1,4, (b) between the two OH groups, (c) without participation of the II atoms of the OH groups. Difficulties encountered in deducing unambiguous fragmentation patterns are discussed.     

Determination of Monomer Unit Sequence Distribution and Linkage Configuration of Copolymers of Styrene and Citraconic Anhydride,and Possibility of a Participation of Electron Donor-Acceptor Complex in the Copolymerization

Abstract

The copolymerization system of styrene (ST) and citraconic (α-methymaleic) anhydride (CA) was found to form semi-alternating copolymers when polymerized with a total monomer concentration of 4 mol/L in CCl₄ at 50°C, with alternating copolymers being formed only when the CA mole fraction in feed was greater than 0.9. More than 50% of the linkage configurations at the cyclic CA units in the copolymers were found to be in cis configuration. This, together with the following observations, is consistent with a participation of the electron donor-acceptor (EDA) complex formed between ST and CA: (a) the complex participation model fits best, although only marginally, to the experimental triad mole fraction of alternating sequences; (b) the alternating monomer unit sequences and the cis linkage configuration at the cyclic CA units are more efficiently formed in non polar CCl₄ solutions than in polar methy ethyl ketone. The equilibrium constant for the EDA complexation of ST and CA in CCl₄ at 23°C is determined to be 0.142 ± 0.015 L/mol.     

A Visible‐Light‐Promoted O‐Glycosylation with a Thioglycoside Donor

Visible‐light irradiation of 4‐p‐methoxyphenyl‐3‐butenylthioglucoside donors in the presence of Umemoto's reagent and alcohol acceptors serves as a mild approach to O‐glycosylation. Visible‐light photocatalysts are not required for activation, and alkyl‐ and arylthioglycosides not bearing the p‐methoxystyrene are inert to these conditions. Experimental and computational evidence for an intervening electron donor–acceptor complex, which is necessary for reactivity, is provided. Yields with primary, secondary, and tertiary alcohol acceptors range from moderate to high. Complete β‐selectivity can be attained through neighboring‐group participation.     

Determination of trace amounts of morpholine and its thermal degradation products in boiler water by HPLC

Summary Morpholine and its amine-type thermal degradation products present in boiler feed water and steam condensate were derivatised with N-succinimidyl-p-nitrophenylacetate. These pre-column derivatives were determined by high-performance liquid chromatography with UV detection at 280 nm. The analytical column was Supelco-sil-ODS with an isocratic mobile phase. Morpholine and its breakdown products were monitored in the range 0.01–10 g ml^–1 with a relative standard deviation of 0.4–3.0%. Chromatographic analysis of boiler feed water and steam condensate samples collected from a boiler servicing a petroleum refinery is described.     

Experimental and Theoretical Studies of Charge Delocalization in Biruthenium–Alkynyl Complexes Bridged by Thiophenes

A series of binuclear ruthenium–alkynyl complexes that are bridged by thiophene groups (thiophene, bithiophene, and terthiophene) have been synthesized. All of these complexes have been well‐characterized by NMR spectroscopy, X‐ray diffraction, and elemental analysis. The electronic properties of these complexes have been examined by using cyclic voltammetry, UV/Vis/NIR and IR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT) calculations. Electrochemical results showed that the potential difference (ΔE) and comproportionation constant (K_c) decreased with increasing size of the thiophene bridging unit. The UV/Vis/NIR spectra and TDDFT calculations of the monocations indicated that the NIR transitions displayed aromatic bridging character. EPR studies of the mono‐oxidized radical species further demonstrated that the unpaired electron/hole was delocalized over both metals and the bridging ligand and established significant participation in the ligand oxidation.     

Stereospecific control of peptide gas‐phase ion chemistry with cis and trans cyclo ornithine residues

We report non‐chiral amino acid residues cis‐ and trans‐1,4‐diaminocyclohexane‐1‐carboxylic acid (cyclo‐ornithine, cO) that exhibit unprecedented stereospecific control of backbone dissociations of singly charged peptide cations and hydrogen‐rich cation radicals produced by electron‐transfer dissociation. Upon collision‐induced dissociation (CID) in the slow heating regime, peptide cations containing trans‐cO residues undergo facile backbone cleavages of amide bonds C‐terminal to trans‐cO. By contrast, peptides with cis‐cO residues undergo dissociations at several amide bonds along the peptide ion backbone. Diastereoisomeric cO‐containing peptides thus provide remarkably distinct tandem mass spectra. The stereospecific effect in CID of the trans‐cO residue is explained by syn‐facially directed proton transfer from the 4‐ammonium group at cO to the C‐terminal amide followed by neighboring group participation in the cleavage of the CO―NH bond, analogous to the aspartic acid and ornithine effects. Backbone dissociations of diastereoisomeric cO‐containing peptide ions generate distinct [b_n]⁺‐type fragment ions that were characterized by CID‐MS³ spectra. Stereospecific control is also reported for electron‐transfer dissociation of cis‐ and trans‐cO containing doubly charged peptide ions. The stereospecific effect upon electron transfer is related to the different conformations of doubly charged peptide ions that affect the electron attachment sites and ensuing N―C_α bond dissociations.     

Investigation of the acceptor properties of chlorophyll in ether and pyridine solutions by a photoconductivity method

Results are given of an investigation of the photoreduction transformations of chlorophyll in diethyl ether and pyridine solutions through measurement of the electrical conductivity during irradiation and by spectral measurements. It is concluded from the experimental data that the red reduced form of chlorophyll a in diethyl ether containing phenylhydrazine is electrically neutral. The possibility of electron transfer between the solvent and chlorophyll molecules during irradiation is examined. A possible model for the participation of the solvent in the primary photochemical act of oxidation-reduction reactions of pigments is proposed.We are indebted to Professor Rassa (France) for pointing out this possible interpretation for the spectrum of III.