The corresponding semiquinone radicals are formed via a one-photon reaction during the irradiation of pyridine, quinoline, isoquinoline, pyrazine, pyrimidine, quinoxaline, and acridine in neutral hydrogen-containing solvents such as ether, methanol, or ethanol. In all cases, the dissolved substance in the nπ*-excited (usually singlet) state splits out a hydrogen atom from the solvent. Six-membered monoaza aromatic compounds on irradiation in methanol acidified with HCl are converted to the same semiquinone radicals as in neutral media, but via a two-photon process consisting of electron transfer from an alcohol molecule to the higher excited triplet state of the protonated monoaza aromatic compound. The corresponding cation radicals are formed by UV irradiation of pyrazine, quinoxaline, and phenazine in methanol acididified with HCl. Six-membered o-diaza compounds of the phthalazine and cinnoline type do not react with ether in the absence of a ketone, which acts as a chemical sensitizer. However, they react with methanol via a two-photon mechanism in which the first step is protonation of the dissolved substance, which is followed by electron transfer.

Abstract—Ultraviolet irradiation of pyrimidine and 4‐ and 5‐methylpyrimidine in methanol at 113 K gave the corresponding semiquinone radicals in a monophotonic process. It is likely that this process involves an n* triplet state of the photoexcited pyrimidines.

Chemischer InformationsdienstVolume 5, Issue 5 Physical Organic Chemistry ChemInform Abstract: PHOTOCHEMICAL STUDIES PART 16, SECOND MOMENT ANALYSIS OF THE ELECTRON SPIN RESONANCE SPECTRA OF RADICALS FORMED BY ULTRAVIOLET IRRADIATION OF 9-PHENYLACRIDINE AND OF ACRIDINE AZELIO CASTELLANO, AZELIO CASTELLANOSearch for more papers by this authorJEAN-PIERRE CATTEAU, JEAN-PIERRE CATTEAUSearch for more papers by this authorALAIN LABLACHE-COMBIER, ALAIN LABLACHE-COMBIERSearch for more papers by this authorGUY ALLAN, GUY ALLANSearch for more papers by this author AZELIO CASTELLANO, AZELIO CASTELLANOSearch for more papers by this authorJEAN-PIERRE CATTEAU, JEAN-PIERRE CATTEAUSearch for more papers by this authorALAIN LABLACHE-COMBIER, ALAIN LABLACHE-COMBIERSearch for more papers by this authorGUY ALLAN, GUY ALLANSearch for more papers by this author First published: February 5, 1974 https://doi.org/10.1002/chin.197405077AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References AZELIO CASTELLANO, JEAN-PIERRE CATTEAU, ALAIN LABLACHE-COMBIER, GUY ALLAN, PHOTOCHEMICAL STUDIES PART 16, SECOND MOMENT ANALYSIS OF THE ELECTRON SPIN RESONANCE SPECTRA OF RADICALS FORMED BY ULTRAVIOLET IRRADIATION OF 9-PHENYLACRIDINE AND OF ACRIDINE, Can. J. Chem., 1973, 51, 3508. DOI: 10.1139/v73-522; 10.1139/v73-522 CASWeb of Science®Google Scholar Volume5, Issue5February 5, 1974 ReferencesRelatedInformation

The irradiation of 9-phenylacridine in methanol, ethanol, or ether leads to the formation of the 9-phenylacridinyl radical. In methanol-d 4 , the radical formed is the singly deuterated analog. The structure of these radicals, which exhibit a hyperfine structure in their e.s.r. spectra measured at 233 °K, is supported by simulation of the spectra using calculated spin densities. The agreement between the experimental and theoretical second moment values of the deuterated radical indicates that the parameters previously chosen for the calculation of the theoretical second moments of pyridinyl-type radicals derived from six-membered ring azaaromatics are suitable and that the second moment method can be used in studies of radicals of this type. We conclude that acridine irradiated in methanol-d 4 leads to the formation of the singly deuterated acridinyl radical.

Chemischer InformationsdienstVolume 3, Issue 2 Isocyclic Compounds ChemInform Abstract: PHOTOCHEMISCHE UNTERSUCHUNGEN 8. MITT. ESR-UNTERSUCHUNG VON CHINOLYL- UND ISOCHINOLYLRADIKALEN G. ALLAN, G. ALLANSearch for more papers by this authorA. CASTELLANO, A. CASTELLANOSearch for more papers by this authorJ. P. CATTEAU, J. P. CATTEAUSearch for more papers by this authorA. LABLACHE-COMBIER, A. LABLACHE-COMBIERSearch for more papers by this author G. ALLAN, G. ALLANSearch for more papers by this authorA. CASTELLANO, A. CASTELLANOSearch for more papers by this authorJ. P. CATTEAU, J. P. CATTEAUSearch for more papers by this authorA. LABLACHE-COMBIER, A. LABLACHE-COMBIERSearch for more papers by this author First published: January 11, 1972 https://doi.org/10.1002/chin.197202127Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume3, Issue2January 11, 1972 RelatedInformation

AbstractBei Bestrahlung in Diäthyläther geht das Chinoxalin (I) in einer Monophotonenreaktion über das intermediäre Radikal (II) in das Substitutionsprodukt (III) als Hauptprodukt über.

Quinoline irradiated in methanol, ethanol or ether leads to radical XV, and isoquinoline to radical XIX. These radicals and the radicals formed from 2 and 4-methylquinoline, 2,4-dimethylquinoline and 3-methylisoquinoline have been studied by ESR at 77°K and at 113°K. Spin densities of the radicals and their second moment have been calculated, experimental and theoretical second moments have nearly the same value. The radicals are formed by a monophotonic process.