Aromatic Hydrocarbon Radical Anions Research Articles

A computational study of solution effects on the disproportionation of electrochemically generated polycyclic aromatic hydrocarbon radical anions. Thermodynamics and structure

Abstract Density functional quantum chemical methods are used to predict the thermodynamics of disproportionation of electrochemically generated polycyclic aromatic hydrocarbon radical anions ( 2 ) into the corresponding neutral species ( 1 ) and dianions ( 3 ). The computations reveal the overwhelming influence of solvation effects upon the disproportionation equilibrium. By comparison, the effect of ion pairing between 3 and the cation of the supporting electrolyte (R 4 N + ) is modest but real. The computational results can be combined with a variety of entropy effects to calculate the spacing Δ E between the first and second reduction potentials of 1 within 100–150 mV. The highly asymmetric structures of the ion pairs between 3 and R 4 N + show little evidence for steric hindrance to ion pairing, yet the computations do show that the strength of the ion pairs does appear to diminish with increasing size of the R group. The strength of the ion pairs with small cations appears to arise out of the large charge-to-size ratio in such cations.

A New Method of Acylation and Formylation of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbon radical anions, prepared by the addition of sodium to the aromatic hydrocarbon in THF, undergo acylation with carboxylic acid esters and formylation with N N-dialkylformamides.

Stoichiometry of protonation of aromatic hydrocarbon radical anions by weak proton donors. A marked discrepancy between the number of protons used and those incorporated into the aromatic structure

The stoichiometries of the reaction between alkali metal radical anions of biphenyl, naphthalene, phenanthrene and anthracene, and methanol and/or other proton donors have been determined by the magnetic titration technique. In the case of naphthalene radical anion and, for example, methanol as the proton source, the stoichiometry was found to be cation-dependent: Li, 2:1; Na, 1.75:1; K, 1.33:1. The reaction products using the experimentally determined stoichiometric conditions were ca. 95% naphthalene and 5% dihydronaphthalene(s). Thus, a marked discrepanc is observed between the protons used and those incorporated into the naphthalene molecule. Radical anions, at concentrations comparable with those of preparative reactions, react with carbon acids or amines according to the first-order kinetic law, although the initial concentrations of the two reactants were of the same order of magnitude or even equal. Lithium anthacene radical anion reacts with phenylacetylene and diethylamine at comparable rates, although the two “acids” differ in their acidities by ca. 10 orders of magnitude. A deuterium isotope effect of 2.49±0.05 was observed in the reaction between lithium anthracene radical anion and diethylamine. A general reaction scheme is proposed that involves electron transfer to the proton and hydrogen-atom attack on the neutral hydrocarbon as the key reaction steps.

Paramagnetic solvent nuclear magnetic resonance shifts in radical anion solutions. 2. Some cation-dependent phenomena in concentrated solutions of aromatic hydrocarbon radical anions and dianions

Paramagnetic solvent nuclear magnetic resonance shifts in radical anion solutions. 2. Some cation-dependent phenomena in concentrated solutions of aromatic hydrocarbon radical anions and dianions

Electrogenerated Chemiluminescence: XXXII . ECL from Energy‐Deficient Aromatic Hydrocarbon Acceptor and Tetrathiafulvalene Donor Systems

The ECL emission from energy‐deficient mixed aromatic hydrocarbon (AHC) acceptor and tetrathiafulvalene (TTF) donor systems has been investigated in acetonitrile. Radical ion annihilation involving TTF radical cations and AHC radical anions was found to result entirely in acceptor fluorescence emission. Energy considerations show that AHC triplet formation followed by triplet‐triplet annihilation to produce the AHC first excited singlet state is the most probable mechanism for the observed ECL. The intermediacy of exciplexes in the ECL process was not observed experimentally.

Formation of intramolecular exciplexes in electrogenerated chemiluminescence

Electrogenerated chemiluminescence of (9-anthracene)-(CH 2) n -(N,N-dimethylaniline) ( n = 0, 1, 2) is discussed. In the electrogenated chemiluminescence spectra, only intramolecular exciplex fluorescence was observed and the local excited fluorescence bands, which were obtained by means of photoexcitation, could not be detected. The efficiency of n = 0 was very large (1.1%) compared with that of the ordinary electron transfer luminescence between the radical anions of aromatic hydrocarbons and the radical cations of aromatic amines (A −1/D + systems). The intramolecular exciplexes seem to be directly formed by electron transfer reactions.

Low-field CIDNP [chemically induced dynamic nuclear polarization] and protonations of aromatic hydrocarbon radical anions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLow-field CIDNP [chemically induced dynamic nuclear polarization] and protonations of aromatic hydrocarbon radical anionsJohn F. Garst and Joseph A. PacificiCite this: J. Am. Chem. Soc. 1975, 97, 7, 1802–1805Publication Date (Print):April 1, 1975Publication History Published online1 May 2002Published inissue 1 April 1975https://doi.org/10.1021/ja00840a032RIGHTS & PERMISSIONSArticle Views47Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (481 KB) Get e-Alerts Get e-Alerts

Electron spin distribution and molecular dynamics of aromatic hydrocarbon radical anions studied by1H and2D N.M.R.

The 1H N.M.R. spectra of the anions of anthracene, pyrene and triphenylene and the 2D N.M.R. spectra of the anions of anthracene-d10 and partly, randomly deuterated triphenylene have been measured in ethereal solutions. The hyperfine splitting constants derived from the measured Fermi contact shifts are presented and compared with E.S.R. data and predictions from theory. From the measured 1H and 2D linewidths the electron spin and rotational correlation times have been calculated. It is shown that the derived rotational correlation times are not very sensitive to anisotropic rotation.

The effects of ion pairing on the EPR spectra of alkyl aromatic hydrocarbon radical anions

It is shown that the calculation of spin density changes in radical anions caused by a counterion can be usefully extended to radicals involving hyperconjugation. Such calculations are done for the acenaphthene and pyracene anions and show that the alternating linewidth effects in their EPR spectra are consistent with proposed double potential minima above the aromatic parts of these radicals. New experiments on acenaphthene are reported which support the calculations. The calculation is shown to account successfully for the effects of ion pair formation in 9,10-dihydroanthracene and in benzocyclobutane. Experiments with partially deuterated dihydroanthracene resolve some uncertainty about the assignment of the coupling constants.

Mechansim of the chemiluminescent reaction of certain alkyl halides with electrogenerated aromatic hydrocarbon radical anions

Mechansim of the chemiluminescent reaction of certain alkyl halides with electrogenerated aromatic hydrocarbon radical anions

The protonation of aromatic hydrocarbon radical anions III. Elucidation of electrode process of aromatic hydrocarbon reduction

The protonation of aromatic hydrocarbon radical anions III. Elucidation of electrode process of aromatic hydrocarbon reduction

The protonation of aromatic hydrocarbon radical anions: III. Elucidation of electrode process of aromatic hydrocarbon reduction

Summary The rates of protonation of aromatic hydrocarbon radical anions with water in the DMF—water systems were measured by the stopped flow method. Apparent first-order rate constants of the order of 10 s−1 were obtained by this method. These rate constants were compared with those calculated from the polarographic limiting currents on the basis of two possible mechanisms, i.e. the e.c.e. mechanism: R + e ⇌ R ⨪ R ⨪ + H 2 O → R H ⋅ + O H − R H ⋅ + e ⇌ R H − and the regeneration mechanism: R + e ⇌ R ⨪ R ⨪ + H 2 O → k R H ⋅ + O H − R H ⋅ + R ⨪ → fast R H − + R Good agreement was found between the rate constants of protonation measured by the stopped flow method and those calculated on the basis of the regeneration mechanism. The regeneration mechanism was justified also by the observation that it leads to rate constants which are independent of drop-time.

The Effect of Water on the Reduction Potentials of Some Aromatic Compounds in the DMF-Water System

Abstract From the viewpoint of the interaction between the oxidized or the reduced form of a depolarizer and solvents, the solvent effect on the half-wave potentials was studied. Another factor affecting the E1⁄2, i.e., pH or ion-pair formation, was also examined. The correction for the liquid junction potential was carried out by the use of the ferrocene standard. The reduction products, radical anions or dianions, were found to be stabilized by the hydrogen-bonding with water where the hydrogen-bond interaction of the dianion was stronger than that of the monoanion. Aromatic hydrocarbon radical anions, whose charges are dispersed over the molecule, were less susceptible to this solvent transfer than were the anthraquinone radical anion and the dianion, whose charges are strongly localized.

The Protonation of Aromatic Hydrocarbon Radical Anions. II. Interpretations of the Rate Constants in Terms of HMO Calculations

Abstract The rates of the protonation of aromatic hydrocarbon radical anions with water in dimethylformamide (DMF)-water mixtures were measured by means of the decay of the visible absorption maxima of radical anions with time. The rates were found to be greatly accelerated by the increasing water content in DMF-water mixtures. This behavior suggests that the negative charge is much more localized in the transition state than in the original radical anion. The rate constants in DMF could be obtained by extrapolation. The correlation of these rate constants to the molecular structure of radical anions was discussed on the basis of the results of HMO calculations. This correlation and the solvent effect could be interpreted by means of the charge-transfer mechanism.

The Protonation of Aromatic Hydrocarbon Radical Anions. I. A Comparison of Methods and a Study of the Mechanism

Abstract The protonation mechanism of the aromatic hydrocarbon radical anions, such as biphenyl, naphthalene, phenanthrene, anthracene, 1,2-benzanthracene, and pyrene, in dimethylformamide (DMF) and water mixtures was studied. Three methods of measuring the concentration of the radical anions, i.e. polarography and ESR and UV absorption spectroscopy, were compared with each other by making simultaneous measurements of the same anthraquinone radical anion solution. A good linear relation of the polarographic anodic diffusion current to the UV absorbance was found, while the ESR signal intensity had linear relations with neither of the others in the system which contained an excessive number of parent molecules, 2×10−3m. The change in the visible absorption spectra of the aromatic hydrocarbon radical anions as a function of the time suggested that all the aromatic hydrocarbon radical anions decay by a first-order reaction. As a result, the radical anions were considered to decay through the following sequence: R\ewdot+H2O\oversetk→RH·+OH−, RH·+R\ewdot\ightleftharpoonsRH−+R, and RH−+H2O\oversetk′→RH2+OH−.

Further information on the structure of some radical anions of aromatic hydrocarbons

1. The EPR spectra of the radical anions formed from diphenylmethane, diphenylethane, and diphenylpropane on reduction with metallic potassium under various conditions and at various temperatures have been discussed. 2. The point of view found in the literature that the delocalization of an electron through saturated methylene bridges in compounds of the type considered is possible has arisen on the basis of inaccurate experiment.

Anionic polymerization of vinyl monomers with condensed aromatic hydrocarbon anions

AbstractThe order of catalytic activity of condensed aromatic hydrocarbon radical anions toward polymerization of acrylonitrile, styrene, and isopren is: naphthalene > anthracene > naphthacene > pentacene.Based on the concept that vinylpolymerization with the hydrocarbon radical anions is initiated by electron transfer from the anion to the vinylmonomer, this order of catalytic activity was theoretically confirmed by calculating the equilibrium constant K in the equilibrium: R⊖ + M ⇌ R + M⊖ (R: hydrocarbon; M: vinylmonomer), where K was evaluated from the half‐wave reduction potential of R and M. The same order was also estimated by the lowest vacant orbital energies corresponding to the electron affinities of R and M.From the apparent number of anions consumed per polymer molecule it was inferred that the smaller the equilibrium constant K with respect to the vinylmonomer, the smaller is the proportion of anions participating in the initiation of polymerization. The devious results with acrylonitrile can be explained by the mechanisms of anionic chain end stabilization suggested by some authors.