Transient spectroscopy and kinetics of the reactions of mesocyclic diamines with tert-butoxyl and with ketone triplets. Effects of ring conformation

Abstract

Absolute rate constants for the reactions of terr-butoxyl and triplet benzophenone, with a series of di-tert-amines have been obtained via laser flash photolysis. These diamines have in common the feature that the nitrogen centers are in the backbone of an aliphatic eight-membered ring at positions 1 and 5. A modest rate enhancement is observed, particularly for 1 in its H-abstraction reaction with tert-butoxyl, which may be explained by the operation of a stereoelectronic effect. From thc absorption maxima of the radical cations of these diamines (produced quenching acetophenone triplets), information concerning the conformations of the eight-membered rings may be inferred. It is concluded that these radical-cations are stabilized by relatively strong through-space bonding interactions between the two nitrogen centers. IntroductionThe study of medium-ring (so-called mesocyclic) systems has provided chemists with a number of surprising results. In particular, heteroatom-substituted eight-membered rings are peculiar. 1,s-Dithiacyclooctane shows appreciable S-S interaction as evidenced by a splitting of 0.43 eV in its photoelectron (PE) spectrum (1). 1,4-Dithiacycloheptane, 13-dithiacyclononane, and 1,6-dithiacyclodecane each shows negligible S-S interaction (<O. 1 eV), indicating that in the eight-membered case the conformation has the two sulfurs in close proximity. Also, electrochemical oxidation of these same bis-sulfides (2) occurs in the range 0.34-0.75 V (1,s-dithiacyclooctane is the most easily oxidized) as compared with normal sulfides 0.66-1.32 V. These oxidation potentials re-

Silyloxyamines as sources of silyl radicals: ESR spin‐trapping, laser flash photolysis investigation, and photopolymerization ability

“…They are ascribed to the radical cation centered on the N‐atom and probably generated through a photoionization process. Indeed, this is consistent with the reported formation of a radical cation upon laser excitation of various aliphatic and aromatic amines in a freon glass,26, 27 for triethylamine, 1‐azabicyclo[3.3.3]undecane, 1‐azabicyclo[2.2.2]octane, or 1,4‐diazabicyclo[2.2.2]octane) in acetonitrile solutions 28, 29. Moreover, time dependent density functional theory (TD‐DFT) calculations on the possible radical cation (at the B3LYP/6‐311G** level; after full geometry optimization) show here that the observed transient spectra for 8‐hydroxyjulolidine and SiN1 , 3‐diethylaminophenol and SiN2 quite satisfactorily correlate with the calculated spectra (vertical bars in Fig.…”

Absolute Kinetics of Aminium Radical Reactions with Olefins in Acetonitrile Solution1

“…Numerous methods have been reported for the generation of aminium radicals, e.g., electrochemistry , and pulse radiolysis. − There are also a number of photogeneration methods, which are of potential use in flash photolysis experiments. One method involves the reduction of sensitizers such as ketone triplets , or dicyanobenzene by amines in an electron transfer quenching reaction, which generates the radical anion of the sensitizer and the radical cation of the amine. Aminium radicals have also been observed from the electron transfer quenching of aromatic radical cations .…”

Kinetics of the reaction hydroxyl + sulfur dioxide in helium, nitrogen, and oxygen at low pressure

“…However, the effect on & 2 due to excited OH radicals cannot be positively ruled out. Although H02 reacts with 03 to form OH H02 + 03 -OH + 202 (17) the slow rate constant Zt17 = 1.1 X 10~14 exp^SOOÍjoo)//] cm1 23 molecule"1 5s"1 suggests that OH regeneration from reaction 17 is unimportant.28 The relative rates of the reactions OH + S02 + M -H0S02 + M (slow)…”