Kinetics and mechanism of the interaction of stable 2,4,6-tri-tert-butylphenoxyl radical with substituted quinones

The kinetics of the reaction of 2,4,6-tri-tert-butylphenoxyl radical with 1,4-benzoquinones was investigated. The composition and structure of the resulting products were established. A reaction mechanism is proposed in which transfer of one electron from phenoxyl to quinone in the initial step followed by rearrangement of the ion-radical pair to an electron-neutral free radical, recombination of which with the starting phenoxyl leads to formation of bis-cyclohexadiene compounds of the corresponding hydroquinones. The reaction rate is determined basically by the electronic influence of the substituents in the quinone, and the possibility of the formation of the final bis-cyclohexadienone is dependent on the steric accessibility of the oxygen in the quinone.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 26, No. 2, pp. 163–168, March–April, 1990.     

Using computers to interpret IR spectra of complex molecules

IR spectroscopy provides a unique fingerprint of compounds and has proven to be extremely valuable in the study of antibiotics. To interpret a spectrum effectively, one often employs an aid, such as a correlation chart or a computer program. This paper describes a program (PAIRS) that automatically interprets IR spectra.     

Reaction of 2,4,6-tri-tert-butylphenoxyl with oxygen in the presence of metal compounds

Conclusions A dependence was found for the isomer composition of the quinolide peroxides formed upon the oxidation of 2,4,6-tri-tert-butylphenol on the coordination capacity of the metal compounds used for the oxidation and the medium. Kinetic measurements showed that the reaction of 2,4,6-tri-tert-butylphenoxyl with oxygen is accelerated in the presence of manganese diacetate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 706–709, March, 1986.     

Triplet states of the amide group. Trapped electron spectra of formamide and related molecules

Trapped electron (TE) spectra are obtained using ion cyclotron resonance detection of scavenged electrons. The lowest singlet-triplet transitions, ³(n→π^*), in formamide (HCONH₂) and N,N-dimethyl formamide (HCONMe₂) are found at vertical energies of 5.30 and 5.00 eV, respectively. An unresolved band containing the ³(π→π^*) and ³(n→3s) states appears at higher energies, centered at 6.60 and 6.00 eV, respectively. The TE spectra of formaldehyde (HCHO), acetaldehyde (MeCHO) and acetone (Me₂CO) are obtained for comparison and are used along with results from ab initio theoretical calculations in establishing assignments. Singlet-triplet transitions dominate the spectra of all of these carbonyl containing molecules, to the exclusion of low lying singlet-singlet transitions. This is in agreement with other TE spectra and the expectation that (dσ/dE) will be higher near threshold for singlet-triplet as compared to singlet-singlet transitions.     

Kinetics of the reaction of the 2,4,6-tri-tert-butylphenoxyl radical with aromatic amines under quasiequilibrium conditions,and the dissociation energy of the N-H bond in aromatic amines

We have studied the kinetics of the reaction of the 2,4,6-tri-tert-butylphenoxyl radical with 11 aromatic amines under quasiequilibrium conditions. The equilibrium constant for each amine was determined from the kinetic results. These values, together with their temperature dependence, were used to calculate the dissociation energy of the N-H bond in the 11 aromatic amines. By using earlier results for the reaction of the aroxyl radical with cumyl hydroperoxide, catalyzed by aromatic amines, we have calculated the rate constants for the reaction of 10 aminyl radicals with cumyl hydroperoxide and of cumylperoxy radicals with 10 aromatic amines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 743–749, April, 1990.     

Controlling electron transfer dynamics in donor-bridge-acceptor molecules by increasing unpaired spin density on the bridge

A t-butylphenylnitroxide (BPNO*) stable radical is attached to an electron donor-bridge-acceptor (D-B-A) system having well-defined distances between the components: MeOAn-6ANI-Ph(BPNO*)-NI, where MeOAn=p-methoxyaniline, 6ANI=4-(N-piperidinyl)naphthalene-1,8-dicarboximide, Ph=phenyl, and NI=naphthalene-1,8:4,5-bis(dicarboximide). MeOAn-6ANI, BPNO*, and NI are attached to the 1, 3, and 5 positions of the Ph bridge, respectively. Time-resolved optical and EPR spectroscopy show that BPNO* influences the spin dynamics of the photogenerated triradical states 2,4(MeOAn+*-6ANI-Ph(BPNO*)-NI-*), resulting in slower charge recombination within the triradical, as compared to the corresponding biradical lacking BPNO*. The observed spin-spin exchange interaction between the photogenerated radicals MeOAn+* and NI-* is not altered by the presence of BPNO*. However, the increased spin density on the bridge greatly increases radical pair (RP) intersystem crossing from the photogenerated singlet RP to the triplet RP. Rapid formation of the triplet RP makes it possible to observe a biexponential decay of the total RP population with components of tau=740 ps (0.75) and 104 ns (0.25). Kinetic modeling shows that the faster decay rate is due to rapid establishment of an equilibrium between the triplet RP and the neutral triplet state resulting from charge recombination, whereas the slower rate monitors recombination of the singlet RP to ground state.     

Electronic structure and spectra of tetrathiotetracene and related molecules

The electronic spectra of tetrathiotetracene (TTT) and of its mono- and dipositive ions have been calculated by the Pariser-Parr-Pople (PPP) method. Furthermore, the band polarizations of the first two bands of TTT have been measured. A reasonable band assignment is given using a new set of PPP parameters based on spectral data of a naphthalene derivative containing similar typical weak S-S bond. Other physical parameters as ionization potential, disproportionation energy, S-S bond length and net π-charges are discussed.     

IR absorption spectra and association of acridinium salts with hydrogen halide molecules

It was observed that the reaction of acridine with hydrogen halides under heterogeneous conditions proceeds in two steps: An acridinium salt is formed in the first step, while a complex of the salt with hydrogen halide molecules is formed in the second step. The formation of a complex leads to substantial changes in the region of the stretching vibrations of NH⁺ bonds, and this makes it possible to propose the direct participation of these bonds in complexing. The band of the stretching vibrations of NH⁺ bonds of the acridinium ion has a complex structure that changes markedly as a function of the sort of halogen ion and replacement of hydrogen by deuterium and in the case of complexing with the hydrogen halide. It is proposed that the structure of this band is due to Fermi resonance.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 99–101, January, 1981.     

Search for highly resolved electron spin resonance spectra of the transient radical in radical polymerization

The detection of highly resolved spectra in electron spin resonance (ESR) measurements of radical polymerization is presented. Well‐resolved ESR spectra of the propagating radical were detected in the radical polymerization of several vinyl monomers with a specially designed cavity and cell. More highly resolved ESR spectra of the propagating radicals of vinyl and diene compounds were observed with aconventional spectrometer without the specially designed cavity and cell. On the basis of the ESR spectra, propagation rate constants and dynamic behavior of propagating radicals are discussed. Moreover, the application of time‐resolved ESR spectroscopy to research on the initiation process in radical polymerization is shown. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 269–285, 2002     

The growth and interaction of conjugated polymer chains,the unpaired electron localization

An ESR method was used to study the structure of the macroradical of the propagating chain R_p in the low-temperature, solid-phase polymerization of p-diethynylbenzene (DEB). The ESR spectra for γ-irradiated DEB samples and those of DEB deuterated in the ethynyl group showed that in the range 77–230 K, the unpaired electron of the macroradical was localized on one of the monomer links. At 230–310 K, its delocalization in a polyconjugated system took place because of addition of a linear macroradical to a double bond of a polymer molecule. The encounter of the macroradical with double bond probably occurs as polymer chain propagation. © 1994 John Wiley & Sons, Inc.     

Optical spectra of protected diamine 10-bond-bridged intervalence radical cations related to N,N,N'N'-tetraalkylbenzidine

The optical absorption spectra of the delocalized intervalence radical cations of seven o,o'-linked benzidine derivatives that have the nitrogens protected as 9-(9-aza-bicyclo[3.3.1]nonan-3-one) derivatives are discussed and compared with that of the p-phenylene radical cation. The linking units are CH2, CH2CH2, NMe, S, SO2, and C=O, and we also studied H,H (the unlinked benzidine). The lowest-energy absorption band is assigned as the transition from the antibonding combination of symmetrical N and aromatic orbitals to the antibonding combination of the antisymmetric N and aromatic orbitals using TD-DFT calculations, and a good correlation between the observed transition energies and those calculated using the simple Koopmans theorem-based "neutral in-cation geometry" calculations on the UB3LYP/6-31G* structures is found. The use of the two-state model that equates the electronic interaction through the bridge between the amino groups with half of the lowest transition energy is seriously incorrect for these and other delocalized intervalence compounds. The problem of extracting the electronic interactions that actually are involved from calculated transition energies is discussed.