Photochemical reactions of radical cations of dimethylformamide in freon matrices at 77 K

Abstract

Spectral characteristics of the radical cations (RC) of DMF (~max = 415 nm, em~ x = (2.6+0.8)" 103 L mol -I cm -1) stabilized in an irradiated glassy freon mixture (CFC13 and CF2BrCF2Br) at 77 K were determined. Amide type radicals and RC of the matrix were shown to be formed by irradiation (~. = 365--436 nm) of the radical cations of DMF in freon matrices using ESR and UV spectroscopy. The quantum yields of photoconversion of the DMF radical cations are independent of the wavelength of exciting light. It was found that the matrix structure affects the processes stabilizing the products of photoconversion of the DMF radical cations.Radical cations (RC) are active intermediates formed in various radiochemi.cal, photochemical, catalytic, etc.

Experimental and theoretical study on the structure and reactions of 1-methoxypropane radical cations

“…This result shows that the main process is the photostimulated charge transfer followed by charge recombination. Similar behavior is observed for the radical cations of other ethers (dimethyl ether, MTBE, tetrahydrofuran) in this matrix [12,13,24]. The signal observed after decay of the radical cations may be tentatively interpreted as a result of superposition of lines from different types of distonic radical cations (e.g., ëç 3 ëç 2 (éç + )ëç 3 and n-ë 3 ç 7 (éç + )…”

“…As shown above, the major part (ca. 60%) of MPE radical cations (as well as MTBE radical cations [13]) decays without the formation of any other radicals under the action of light at 436-546 nm in a CFCl 3 matrix at 77 K. By analogy with the cases of radical cations of n-alkanes [15] and tetrahydrofuran [24], we may conclude that this effect is due to photostimulated charge transfer (5) from the MPE radical cation to matrix followed by charge migration and recombination of the radical cations with matrix radical anions (6):…”

Formation of DMSO and DMF radicals with minute amounts of base

“…20 DMSO and DMF radicals have otherwise been generated by rather harsh conditions (photolysis, pulse radiolysis, sonication) and detected at low temperatures. 22 Although we lack the opportunity at the moment to describe the reactions and products in detail we think it advisable to present here the spectra and chemical data verifying radical formation in neat DMSO and DMF and in solvent mixtures after addition of small quantities of base.…”

“…[18][19][20] Other peculiar observations have been articulated: DMSO played an ambiguous role in creating radicals during the alkaline degradation of carbohydrates. 21 Unexpected radicals emerged in the Reissert reaction when performed in DMF with NaH, 22 although it was explicitly stated that no radicals are obtained in alkaline DMF. 20 DMSO and DMF radicals have otherwise been generated by rather harsh conditions (photolysis, pulse radiolysis, sonication) and detected at low temperatures.…”

Electron Localization and Radiation Chemistry of Amides

“…For N,N′-dialkylformamides (1 in Scheme 1), the parent radical cation {R 2 NCHO} +• can be observed at low temperature in a freon matrix. 21,22 As the sample temperature increases, this radical cation deprotonates (mainly) from the H α position of the aliphatic arms, forming radical 2 and proton adduct 4; this deprotonation can also occur internally, by lightinduced isomerization of the parent radical cation. 21 In the gas phase (Table S1 in the Supporting Information), reaction 5 is exergonic by 0.58 eV and reaction 6 is exergonic by 0.73 eV; other modes for fragmentation (Table S1 in the Supporting Information) are endergonic, and so can only involve electronically excited "holes" formed in the course of ionization.…”