Aromatic Free Radicals Research Articles

Aromatic free radicals in the gunflint chert

The Middle Precambrian chert of Gunflint formation contains an exceptionally high amount of bitumen free radicals. The Gunflint chert appears to be the oldest formation in which the presence of these radicals has been found. Their presence in this deposit constitutes evidence for the existence of primitive protovascular plants in the early Proterozoic environment of the Lake Superior Region of Canada.

Electronic Spectra of Some Aromatic Free Radicals

Abstract Electronic spectra are reported for 1-indanyl, 1-tetralyl, and 1-indenyl radicals generated photolytically or radiolytically in rigid matrices; the former two radicals show spectral features similar to those of benzyl radical, whereas the latter radical has a different spectrum because of its non-alternant π electron system.

Kinetics of geminate recombination of aromatic free radicals

Nanosecond laser flash photolysis techniques were used to observe the geminate recombination kinetics of 2-(4'-diphenylaminophenyl)-indandione-1,3-yl radicals (R) in vaseline oil at 0°C. The kinetics are closely described by the Kofman-Burshtein model. The rate of diffusion-controlled recombination of R by random encounters in the bulk was also measured. The kinetics of geminate recombination and recombination in the bulk are described by the same parameters (diffusion coefficient (1.8 ± O.6) × 10 −8 cm 2/s and reaction radius 13.2Å).

The role of free radicals and molecular size in mesophase pitch

The melting behavior of polynuclear aromatic hydrocarbons and hydrocarbon free radicals was studied with differential scanning calorimetry and hot-stage microscopy. Mesophase was not observed during melting of large aromatic compounds, including some containing as many as nine condensed rings. Synthetic aromatic free radicals derived from benzanthrene and naphthanthrene did not induce the formation of mesophase when melted with other polynuclear hydrocarbons. The development of mesophase in pitch is attributed to an increase in molecular size as a result of thermal polymerization.

Observation of deuterium quadrupole splittings of aromatic free radicals in liquid crystals by ENDOR and TRIPLE resonance

First measurements of deuterium quadrupole coupling constants of a polyatomic doublet state radical are reported. The quadrupole couplings were determined by ENDOR and electron–nuclear–nuclear TRIPLE resonance in liquid crystals. For the partially deuterated perinaphthenyl radical the out-of-plane component of the deuterium quadrupole coupling was measured to be e2q33Q/h =−(94±3) kHz for both molecular sites. Within experimental error these values are equal to those measured earlier for deuterated alternant hydrocarbons in the diamagnetic singlet ground state.

Electrostatic energy of aromatic ion radical crystals

The electrostatic energy of aromatic charge-transfer (CT) and free radical (FR) crystals is obtained by using the many-electron site representation and the modified Hubbard model previously developed to correlate the unusual magnetic, electric and optical properties of CT and FR crystals. Both π-electron overlap between adjacent ion radicals in a stack and configuration interaction with CT states are included, thus improving on the Madelung approximation of disjoint charge distributions. π-electron overlap leads to a Coulomb exchange energy E ex which stabilizes both ionic CT and FR crystals, while configuration interaction scales the ground state charge densities, and thus the Madelung energy, in CT crystals. E ex is obtained for 1 : 1 CT crystals and a numerical estimate of 10–15 kcal/mole is found for both TMPD-TCNQ and for TMPD-chloranil.

Fluorine-19 hyperfine splittings in the electron spin resonance spectra of fluorinated aromatic free radicals. III. Benzophenone anion radicals

Fluorine-19 hyperfine splittings in the electron spin resonance spectra of fluorinated aromatic free radicals. III. Benzophenone anion radicals

Fluorine-19 hyperfine splittings in the electron spin resonance spectra of fluorinated aromatic free radicals. II. Triphenylmethyl radicals

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFluorine-19 hyperfine splittings in the electron spin resonance spectra of fluorinated aromatic free radicals. II. Triphenylmethyl radicalsShrikant V. Kulkarni and Charles TrappCite this: J. Am. Chem. Soc. 1970, 92, 16, 4801–4808Publication Date (Print):August 1, 1970Publication History Published online1 May 2002Published inissue 1 August 1970https://doi.org/10.1021/ja00719a007RIGHTS & PERMISSIONSArticle Views188Altmetric-Citations38LEARN 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 (1008 KB) Get e-Alerts Get e-Alerts

Electron spin resonance of stable aromatic radical intermediates in pyrolysis

This paper presents the results of electron spin resonance measurements on several types of stable aromatic free radicals suspected as intermediates in carbonization. The radicals studied include phenalenyl, 1-methylphenalenyl, 1-phenylphenalenyl, fluorenyl, 9-phenylfluorenyl, and biphenyleneallyl. The radicals all show remarkable stability at high temperatures. For at least a limited group of compounds, a correlation appears to exist between the planarity of free radical intermediates formed during carbonization and the degree of order of the final graphites.

20th Farkas Memorial Lecture Recent Progress in the Study of Transient Chemical Intermediates

AbstractRecent studies of aromatic free radicals and electronically excited states using flash photolytic techniques in the microsecond and nanosecond ranges are reviewed. The technique and applications of laser flash photolysis are discussed.

Anomalous Magnetic Properties of Stable Crystalline Phenoxyl Radicals

Abstract The results of static magnetic susceptibility measurements in the 1.8–300°K temperature range are reported on powder samples of the stable aromatic free radicals: 2,6-di-t-butyl-4(3,5-di-t-butyl-4-oxocyclohexa-2,5-dienylidene methyl) phenoxyl (Galvinoxyl) and 2,6-di-t-butyl-4(3,5-di-t-butyl-4-oxocyclohexa-2,5-dienylidene amino) phenoxyl (BIP) radicals. The susceptibility of Galvinoxyl follows the Curie-Weiss law above Tc=81±1°K, depending on the sample, with a Weiss constant of 11±3°K. However, at Tc=81°K, χp rapidly decreases, and below 66°K the susceptibility again increases, with different spin concentrations for independently-prepared samples as the temperature is lowered. A maximum at 81°K was also found by the EPR measurements; the anomaly of the susceptibility at this temperature is probably due to a first-order phase transition induced magnetically, accompanying the pairing of magnetic spins, judging from the results of differential thermal analysis and the magnetic susceptibility measurements. On the other hand, the magnetic susceptibility of the BIP radical exhibits a broad maximum at 54±2°K. This susceptibility can be explained approximately using a model which consists of a singlet ground state and a triplet state lying slightly above the ground state.

Fluorine-19 hyperfine splittings in the electron spin resonance spectra of fluorinated aromatic free radicals

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFluorine-19 hyperfine splittings in the electron spin resonance spectra of fluorinated aromatic free radicalsShrikant V. Kulkarni and Charles TrappCite this: J. Am. Chem. Soc. 1969, 91, 1, 191Publication Date (Print):January 1, 1969Publication History Published online1 May 2002Published inissue 1 January 1969https://doi.org/10.1021/ja01029a035RIGHTS & PERMISSIONSArticle Views73Altmetric-Citations8LEARN 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 (152 KB) Get e-Alerts Get e-Alerts

Absorption spectra of aromatic free radicals: a vibrational analysis of the 3050 Å absorption spectrum of benzyl and a new transition of phenoxyl

The diffuse structure in the 3050 Å absorption spectrum of the benzyl radical has been interpreted in terms of vibrational frequencies similar to those active in the ultraviolet absorption of toluene. A new spectrum of the phenoxyl radical in the region of 6000 Å is described and assigned to a π ← n transition.

Substituent effects on the properties of stable aromatic free radicals. Oxidation-reduction potentials of triarylamine-triarylaminium ion systems.

Substituent effects on the properties of stable aromatic free radicals. Oxidation-reduction potentials of triarylamine-triarylaminium ion systems.

Paramagnetism of Carbazyl and Hydrazyl Free Radicals

Static magnetic-susceptibility measurements in the temperature range 1.4°—300°K are reported on powder samples of the stable aromatic free radicals N-picryl−9-aminocarbazyl (PAC), 2,2-diphenyl−1-picrylhydrazyl in the 106°C mp [DPPH(I)] and 137°C mp [DPPH(II)] crystal modifications, 2-phenyl−2-p-nitrophenyl−1-picrylhydrazyl (DHNO2·) and 2,2-bis(p-nitrophenyl)−1-picrylhydrazyl [D(NO2)2·]. Radical concentrations in the range from 0.81 to 0.99 and Weiss constants in the range −36° to −5.2°K are determined. The measurements are interpreted assuming that the magnetic behavior is due to alternating antiferromagnetic exchange-coupled linear chains. Exchange integrals are inferred from fitting theoretical curves to the susceptibility maxima. Evidence is presented for the presence of random dilution by diamagnetic sites in PAC.

E.s.r. spectra of some aromatic free radical anions which contain cumulated and unsaturated chains

The free-radical-anions af α,γ-diphenylbutadiene, diphenyldiacetylene, tetraphenylethylene, tetraphenylbutatriene, tetraphenylhexapentaene, dibiphenylene-ethylene and dibiphenylenebutratriene have been produced in solution by reduction with potassium. Well-resolved e.s.r. spectra of the radical-anions have been recorded. Except for tetraphenylethylene the spectra have been completely analyzed and the experimental h.f.s.c. compared with the values calculated by the Huckel and McLachlan methods. For tetraphenylethylene, partial analysis of the spectrum has been achieved and two h.f.s.c. and the total spectrum width have been determined. All attempts to produce the free-radical-anion of tetraphenylallene failed. This has been discussed in terms of the probable electron-affinity of this molecule.

Substituent Effects on the Properties of Stable Aromatic Free Radicals. The Criterion for Non-Hammett Behavior1

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSubstituent Effects on the Properties of Stable Aromatic Free Radicals. The Criterion for Non-Hammett Behavior1Robert I. WalterCite this: J. Am. Chem. Soc. 1966, 88, 9, 1923–1930Publication Date (Print):May 1, 1966Publication History Published online1 May 2002Published inissue 1 May 1966https://doi.org/10.1021/ja00961a014RIGHTS & PERMISSIONSArticle Views794Altmetric-Citations125LEARN 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 (1000 KB) Get e-Alerts Get e-Alerts

Substituent Effects on the Properties of Stable Aromatic Free Radicals. An LCAO-MO Treatment1

Substituent Effects on the Properties of Stable Aromatic Free Radicals. An LCAO-MO Treatment¹

The calculation of positive ancl negative spin densities in aromatic free radicals

A simple method of calculating the unpaired π electron spin density is proposed which equates the unpaired spin density to the difference between a density of n-1 electrons of a spin and a density of n electrons of β spin. The α spin density is found from an SCF-Pariser-Parr type calculation for 2(n+l) electrons in n + 1 closed shells and the β spin density from a calculation on 2n electrons in n, closed shells. Positive and negative spin densities are found which are in excellent agreement with experiment. These results are compared to spin densities calculated by other methods, and an improvement is noted in the representative cases considered.

Measurement of g Values in the Electron Spin Resonance Spectra of Free Radicals

Measurements have been made of the g values in the electron spin resonance spectra of 20 aromatic free radicals with an accuracy which has not previously been attainable. The largest source of error for both absolute and relative measurements resulted from variations in the difference between the magnetic field at the ESR sample and at the proton NMR probe, located just outside the center of the microwave cavity, which was used to measure the field. Except for the p-benzosemiquinone radical, g values were not found to depend on temperature over the range from room temperature to −100°C. The dependence of the g value on solvent and counterion was also investigated to some extent, and the g value of the perinaphthenyl radical was found to vary markedly with solvent. Agreement with Stone's theory of the g values of aromatic radicals is excellent, except for those radicals in which molecular distortions are expected according to the Jahn—Teller theorem and for radicals in which the unpaired electron is in a nonbonding molecular orbital.