Probing radical pathways in electrophilic addition of halogens: Classical vs. bridged intermediates

George, Lisa; Kalume, Aimable; Reid, Scott A.

doi:10.1016/j.cplett.2012.10.034

Cited by 7 publications

(9 citation statements)

References 23 publications

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“…Considering that the open-form C 2 H 4 Cl and C 2 F 4 I radicals and the bridged-form C 2 H 4 I radical have been clearly identified in matrices with IR spectra, we were interested to explore the structure of the C 2 H 4 Br • radical by IR absorption. We took advantage of the diminished cage effect of solid para -hydrogen ( p- H 2 ) to investigate the infrared spectrum of C 2 H 4 Br • via photodissociation of a matrix of C 2 H 4 /Br 2 / p -H 2 followed by annealing.…”

Section: Introductionmentioning

confidence: 99%

Formation and Infrared Spectrum of the Open-Form 2-Bromoethyl Radical (2-C₂H₄Br^•) from Ultraviolet Irradiation of a C₂H₄/Br₂/p-H₂ Matrix

2021

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The addition reaction of halogens to alkenes is important in organic synthesis, but the reaction intermediate has rarely been detected. Whether the structure of the intermediate bromoethyl (C 2 H 4 Br • ) radical is a bridged form or an open form is unclear. We took advantage of the diminished cage effect of solid p-H 2 and employed infrared (IR) absorption to record the IR spectrum of C 2 H 4 Br • after photolysis of a C 2 H 4 /Br 2 /p-H 2 matrix at 254 nm, followed by annealing. New spectral features at 676.9, 776.7, 1068.5, 1148.0, 3041.8, and 3126.8 cm −1 are assigned to the open-form 2-bromoethyl radical, according to their photolytic behavior and comparison with scaled harmonic vibrational wavenumbers and IR intensities calculated with the B2PLYPD3/ 6-311++G(2df,2p) method.

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Section: Introductionmentioning

confidence: 99%

Formation and Infrared Spectrum of the Open-Form 2-Bromoethyl Radical (2-C₂H₄Br^•) from Ultraviolet Irradiation of a C₂H₄/Br₂/p-H₂ Matrix

2021

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“…Other related experiences, like the photochemistry of small olefin molecules with dihalogens in solid argon, have been explained also by means of radical addition reactions. For instance, the both stable conformers ( trans and gauche ) of XCH 2 –CH 2 X molecules (X = Br or I) were formed by irradiation of matrix-isolated complexes C 2 H 2 ···X 2 with visible light (λ > 300 nm). , These results were explained by means of a radical mechanism, in which a haloalkyl radical intermediate, XC 2 H 2 , was formed after cleavage of the dihalogen bond. Likewise, a radical addition reaction explains formation of the syn and anti forms of ClC(O)SeF as represented in Scheme .…”

Section: Resultsmentioning

confidence: 99%

Photochemical Reaction of OCSe with ClF in Argon Matrix: A Light-Driven Formation of XC(O)SeY (X, Y = F or Cl) Species

et al. 2017

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The photochemistry of OCSe with ClF trapped together in argon matrices at cryogenic temperatures has been explored and the first interhalogen representatives of the elusive XC(O)SeY family, namely syn-ClC(O)SeF, anti-ClC(O)SeF, syn-FC(O)SeCl, and anti-FC(O)SeCl, as well as the hitherto triatomic species ClSeF complexed by a CO molecule, were obtained. Both ClC(O)SeF conformers appear to be produced independently by photolysis of the respective precursors; while formation of both FC(O)SeCl structures is ruled by the presence of an angular molecular complex OCSe···Cl-F formed prior to photolysis. This latter photochemical pathway seems to favor the formation of the less stable anti-FC(O)SeCl structure instead of the more stable syn- one. With the aid of quantum chemical calculations, using ab initio, DFT, TDDFT, and CASSCF methods, the mechanism for this photochemical reaction is rationalized both in terms of radical processes as well as a photoinduced electron transfer occurring into the OCSe···Cl-F complex. Also a singlet-triplet conical intersection between anti and syn rotamers of the FC(O)SeCl molecule is theoretically explored.

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“…carried out with the UM06-2x functional (see Figure S1 in the Supporting Information) because it yields similar profiles of the potential energy curves than those obtained with the UCCSD approximation of open shell systems 13 and it has been successfully used in the study of complexes formed by radicals with closed shell molecules. 28 The same methodology was used to examine the degradation pathway via isomerization/fragmentation, 10 characterized by the rearrangement of the 2-methylfuran moiety to the pyrylium cation (see Figure S1 in the Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

Electronic Structure and Noncovalent Interactions within Ion–Radical Complexes of N-(2-Furylmethyl)aniline Molecular Ions

Narváez

Rocha‐Rinza

2015

J. Phys. Chem. A

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We investigate the electronic structure and noncovalent interactions within cation-radical complexes that are relevant in the electron impact mass spectrometry of N-(2-furylmethyl)anilines, 4-R-C6H4-NH-CH2-C4H3O with (R = -H, -OCH3, -CH3, -F, -Cl, -Br). In particular, we consider the reactive intermediates that precede the final products of two previously suggested dissociation pathways for these systems, i.e., (i) a direct cleavage of the NH-CH2 bond and (ii) an isomerization/fragmentation mechanism. The study is performed by means of correlated calculations (UCCSD and UMP2) together with density functionals (UM06 an UM06-2x) along with the triple-ζ quality basis set 6-311++G(2d,2p). In addition, we carried out a topological analysis of the electron density in accordance with the quantum theory of atoms in molecules (QTAIM) together with the examination of the noncovalent interaction (NCI) index. In contrast with previous studies based on the UB3LYP approximation, we could determine the transition states associated with both fragmentation pathways. The Rice-Ramsperger-Kassel-Marcus theory, used to determine the relative importance of these dissociation mechanisms, indicates that whereas the direct cleavage and the isomerization/fragmentation reaction routes have similar constant rates at low energy, the former prevails when the energy of the system is increased. The QTAIM analysis reveals that the charge of the cation-radical complex is mainly located on either a furfuryl (direct cleavage mechanism) or a pyrylium (isomerization/fragmentation pathway) ion and that these units interact with a neutral radical aniline moiety. The localization of the positive charge in either a furfuryl or pyrylium cation is in agreement with the preminecence of the m/z = 81 fragment in the mass spectrometry of N-(2-furylmethyl)anilines. Moreover, the QTAIM properties indicate that the α unpaired electron of the system is principally distributed over the nitrogen and the ortho and para carbon atoms with respect to the -NH group in the R-C6H4-NH unit. The investigation of the NCI index and the intermolecular bond critical points and bond paths gives an account of the NCIs linking the radical cation clusters under consideration. Finally, we found correlations which indicate that the concentration of the m/z = 81 fragment in a mass spectrum is reduced with the interaction energy of the radical complex from which it is originated. Altogether, this work shows how the combination of suitable electronic structure calculations along with post wave function analyses can yield important insights about the formation and properties of cation-radical complexes relevant in mass spectrometry.

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Probing radical pathways in electrophilic addition of halogens: Classical vs. bridged intermediates

Cited by 7 publications

References 23 publications

Formation and Infrared Spectrum of the Open-Form 2-Bromoethyl Radical (2-C₂H₄Br^•) from Ultraviolet Irradiation of a C₂H₄/Br₂/p-H₂ Matrix

Formation and Infrared Spectrum of the Open-Form 2-Bromoethyl Radical (2-C₂H₄Br^•) from Ultraviolet Irradiation of a C₂H₄/Br₂/p-H₂ Matrix

Photochemical Reaction of OCSe with ClF in Argon Matrix: A Light-Driven Formation of XC(O)SeY (X, Y = F or Cl) Species

Electronic Structure and Noncovalent Interactions within Ion–Radical Complexes of N-(2-Furylmethyl)aniline Molecular Ions

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Probing radical pathways in electrophilic addition of halogens: Classical vs. bridged intermediates

Cited by 7 publications

References 23 publications

Formation and Infrared Spectrum of the Open-Form 2-Bromoethyl Radical (2-C2H4Br•) from Ultraviolet Irradiation of a C2H4/Br2/p-H2 Matrix

Formation and Infrared Spectrum of the Open-Form 2-Bromoethyl Radical (2-C2H4Br•) from Ultraviolet Irradiation of a C2H4/Br2/p-H2 Matrix

Photochemical Reaction of OCSe with ClF in Argon Matrix: A Light-Driven Formation of XC(O)SeY (X, Y = F or Cl) Species

Electronic Structure and Noncovalent Interactions within Ion–Radical Complexes of N-(2-Furylmethyl)aniline Molecular Ions

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Formation and Infrared Spectrum of the Open-Form 2-Bromoethyl Radical (2-C₂H₄Br^•) from Ultraviolet Irradiation of a C₂H₄/Br₂/p-H₂ Matrix

Formation and Infrared Spectrum of the Open-Form 2-Bromoethyl Radical (2-C₂H₄Br^•) from Ultraviolet Irradiation of a C₂H₄/Br₂/p-H₂ Matrix