“…Some computational and experimental data are available also for alkyl-substituted cyclohexane radical cations. [947][948][949][950][951] Cycloalkane functionalization via radical cations was developed in solution. 952,953 For instance, cyclohexyl-benzene-1,2,4-tricarbonitrile was obtained in 80% yield after SET oxidation of cyclohexane with photoexcited TCB (Scheme 25).…”
Section: Medium-sized Cycloalkanesmentioning
confidence: 99%
“…The cyclohexane radical cation is C 2 h -symmetric with two long C−C bonds; the C s starting structure converges to C 2 h during the optimization 919 (Figure ). Some computational and experimental data are available also for alkyl-substituted cyclohexane radical cations. − 19 Structures of cyclopentane and cyclohexane radical cations at B3LYP/6-111G( d , p ) …”
“…Some computational and experimental data are available also for alkyl-substituted cyclohexane radical cations. [947][948][949][950][951] Cycloalkane functionalization via radical cations was developed in solution. 952,953 For instance, cyclohexyl-benzene-1,2,4-tricarbonitrile was obtained in 80% yield after SET oxidation of cyclohexane with photoexcited TCB (Scheme 25).…”
Section: Medium-sized Cycloalkanesmentioning
confidence: 99%
“…The cyclohexane radical cation is C 2 h -symmetric with two long C−C bonds; the C s starting structure converges to C 2 h during the optimization 919 (Figure ). Some computational and experimental data are available also for alkyl-substituted cyclohexane radical cations. − 19 Structures of cyclopentane and cyclohexane radical cations at B3LYP/6-111G( d , p ) …”
“…In the absence of distortions due to second-order effects, the JT potential energy surface on which these two states are located should show three equivalent minima and three equivalent transition states interconnecting them, all of C 2 v symmetry . UHF/6-31G** geometry optimizations in C 2 v predicted the 2 A 2 state to be slightly more stable than its 2 B 1 counterpart, , which led the authors of this study to suggest that the effective D 3 h symmetry and the coupling to six equivalent protons observed in the ESR spectrum at 4 K are brought about by averaging of three equivalent 2 A 2 structures. For these structures, INDO calculations yielded 1 H hyperfine-coupling constants a H of +0.20 mT for the two methylene α-protons at C-3 and −1.37 mT ( endo )/−1.44 mT ( exo ) for the two pairs of such protons at C-1 and C-2. , Conversely, the corresponding a H values for the 2 B 1 structure were predicted as −1.99 mT for the two protons at C-3 and −0.35 mT ( endo )/−0.29 mT ( exo ) for those at C-1 and C-2.…”
Section: Calculations and Discussionmentioning
confidence: 79%
“…The corresponding radical cation (TMM •+ ) is a 3π-electron system, in which the bonding MO ψ 1 is doubly occupied and the unpaired electron is shared by the NBMOs ψ 2+ and ψ 2 - ;i.e., TMM •+ has a degenerate ground state subject to Jahn−Teller (JT) distortion. , The first attempts to observe the ESR spectrum of TMM •+ after γ-irradiation of methylenecyclopropane (MCP) in CFCl 3 , CF 3 CCl 3 , and CF 2 ClCFCl 2 matrices at 77 K had failed, and only the spectra of the triplet TMM •• ,6a and a few other, not fully identified species were detected. , Eventually, use of CF 2 ClCF 2 Cl or perfluorinated methylcyclohexane (CF 3 -c-C 6 F 11 ) as matrix led to an ESR spectrum consistent with that expected for TMM •+ . This spectrum exhibits seven lines spaced by 0.93 mT with a binomial distribution of intensities, which indicates an effective D 3 h symmetry.…”
Upon ionization by gamma-irradiation in frozen CFCl(3), or by X-irradiation in an Ar matrix, 2,2,3,3-tetramethylmethylenecyclopropane (MCP-Me4) readily undergoes ring opening to yield the radical cation of 1,1,2,2-tetramethyltrimethylenemethane (TMM-Me4). The hyperfine-coupling constants for TMM-Me4(.+) are (mT) -1.99 (2H), +0.53 (6H), and +0.19 (6H), and the singly occupied orbital closely resembles one of the two degenerate nonbonding pi-MOs (NBMOs) of trimethylenemethane (TMM). Due to the expected effect of the methyl substituents, this "symmetric" NBMO, psi(2+) (b(1)), is energetically favored relative to its "antisymmetric" counterpart, psi(2-) (a(2)), so that the ground state assumes a structure with (2)B(1) symmetry in the C(2v) point group. Calculations show that the ring opening in the primary radical cation MCP-Me4(.+) to yield TMM-Me4(.+) is spontaneous, whereas in the parent system (MCP(.+) --> TMM(.+) a low barrier does exist. In contrast to the previously investigated case of the radical cation of tetramethyleneethane, the "electromer" of TMM-Me4(.+), in which the unpaired electron occupies psi(2-), cannot be attained photochemically.
“…The temperature dependence of the spectra was successfully explained in terms of nuclear spin-rotation couplings using a three-dimensional free quantum-rotor model. That is, applying the Pauli principle the A 1 -lines with the 1:1:1:1 quartet of the CH 3 radical was attributed to the four totally symmetric A 1 nuclear spin states coupled with the rotational ground state, J = 0, in D 3 symmetry. , On the other hand, the E -lines were attributed to the nuclear spin states coupled with the J = 1 rotational state. , Furthermore, the interesting abnormal intensities observed for the D-labeled methyl radicals, CH 2 D, CHD 2 , and CD 3 , and their temperature dependences were fully analyzed by the nuclear spin-rotation couplings …”
High-resolution electron spin resonance (ESR) spectra of radical pairs of a hydrogen atom that coupled with a methyl radical (H...CH3, H...CHD2, D...CH2D, and D...CD3) were observed for X-ray irradiated solid argon containing selectively deuterium-labeled methanes, CH4, CH2D2, and CD4, at 4.2 K. The double-quartet 1H-hyperfine (hf) splittings of ca. 26 and 1.16 mT at the Deltam(s) = +/-1 and Deltam(s) = +/-2 transitions, which are one-half of the isotropic 1H-hf splittings of an isolated H-atom and a CH3 radical, were attributed to the H...CH3 pair. The 1H-hf splittings at the Deltam(s) = +/-1 transition were further split by the fine structure (fs) due to the electron dipole-dipole coupling. Because of the high-resolution spectra, three different sets of the fs splitting, d, are clearly resolved in the spectra of both the H...CH3 and the D...CD3 pairs. The separation distance (inter-spin distance), R, between the H-atom and the CH3 radical being in pairs was evaluated from the d values based on a point-dipole interaction model. For the case of the H...CH3 pair, the observed d values of 4.2, 4.9, and 5.1 mT yield the respective separations, R = 0.87, 0.83, and 0.82 nm, to probe the trapping site of the pair in an Ar crystalline lattice (fcc). For the pair with R = 0.87 nm, for example, we propose that the CH3 radical occupies a substitutional site and the counter H-atom occupies either the interstitial tetrahedral sites directed away from the CH3 radicals by a distance of 0.87 nm or the interstitial octahedral sites by a distance of 0.88 nm. When a mixture of CH4 and CD4 in a solid Ar matrix was irradiated, only two different radical pairs, H...CH3 and D...CD3, were observed. This result clearly demonstrates that the hydrogen atom and methyl radicals, which undergo a pairwise trapping, can originate from the same methane molecule.
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