Quinoline Triradicals: A Reactivity Study (original) (raw)
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The Journal of Physical Chemistry, 1991
we find that it fails completely, emphasizing once again the difficulties one encounters in explaining the experimental results. One possibility for extending the scope of the BEBO model to embrace these reactions is to assume that the two parameters of the Sat0 triplet function, the Morse parameter 8, and S i 4 electronic dissociation energy, E,, which are interconnected, are dependent on methylation. Taking E, = 540 kJ/mol and 8 = 2.1 A-' for 0 + SiH,, and E, = 520 kJ/mol and 0 = 2.25 A-' for 0 + Me3SiH, (for other parameters see ref 1) one obtains the results presented in . The trend in the rate constants with methylation can be satisfactorily reproduced but the Arrhenius parameters and kinetic isotope effects are in much worse agreement with the corresponding experimental values than is the case for the 0 + alkane system.21
Energetics and chemical bonding of the 1,3,5-tridehydrobenzene triradical and its protonated form
Chemical Physics, 2005
Quantum chemical calculations were applied to investigate the electronic structure of the parent 1,3,5-tridehydrobenzene triradical (C6H 3, TDB) and its anion (C6H3-), cation (C6H3+) and protonated form (C6H4+). Our results obtained using the state-averaged complete active space self-consistent-field (CASSCF) followed by second-order multi-state multi-configuration perturbation theory, MS-CASPT2, and MRMP2 in conjunction with the large ANO-L and 6-311++G(3df,2p) basis set, confirm and reveal the followings: (i) TDB has a doublet 2A1 ground state with a 4B2-2A1 energy gap of 29 kcal/mol, (ii) the ground state of the C6H3-anion in the triplet 3B2 being 4 kcal/mol below the 1A 1 state. (iii) the electron affinity (EA), ionization energy (IE) and proton affinity (PA) are computed to be: EA = 1.6 eV, IE = 7.2 eV, PA = 227 kcal/mol using UB3LYP/6-311++G(3df,2p) + ZPE; standard heat of formation ΔHf(298 K, 1 atm)(TDB) = 179 ± 2 kcal/mol was calculated with CBS-QB3 method. An atoms-in-molecules (AIM) analysis of the structure reveals that the topology of the electron density is similar in all compounds: hydrogens connect to a six-membered ring, except for the case of the 2A2 state of C6H4+ (MBZ+) which is bicyclic with fused five-and three-membered rings. Properties of the chemical bonds were characterized with Electron Localization Function (ELF) analysis, as well as Wiberg indices, Laplacian and spin density maps. We found that the radicals form separate monosynaptic basins on the ELF space, however its pair character remains high. In the 2A1 state of TDB, the radical center is mainly localized on the C1 atom, while in the 2B2 state it is equally distributed between the C3 and C5 atoms and, due to the symmetry, in the 4B2 state the C1, C2 and C3 atoms have the same radical character. There is no C3-C5 bond in the 2A1 state of TDB, but the interaction between these atoms is strong. The ground state of cation C6H3+ (DHP), 1A1, is not a diradical and has a doubly aromatic character. Aromaticity of the different compounds was studied within the ELF framework and the standard deviation of the bond lengths and bond orders. The Jahn-Teller distorted 2A1 and 2B2(C2v) states of TDB were found to exhibit an aromaticity comparable to that of benzene. Overall protonation of the TDB reinforces the stability of the low-spin doublet states, the classical Hund's rule is not obeyed. In a view, these species could better be regarded as radicals than triradicals.
The Journal of Physical …, 2001
The mechanism for the C(3 P) + C 2 H 3 reaction has been studied via ab initio calculations to investigate possible formations of C 3 H 2 and C 3 H isomers in an extraterrestrial environment, combustion processes, and CVD. The C(3 P) + C 2 H 3 reaction, which produces C 3 H 3 radical intermediates on the ground-state potential energy surface (PES), is studied employing the B3LYP/6-311G(d,p) and RCCSD(T)/6-311+G(3df,2p) levels of theory. Initially formed C 3 H 3 intermediates have enough energy to undergo unimolecular rearrangements. Further, H or H 2 eliminations then lead to C 3 H 2 or C 3 H fragments. The most energetically favorable channel is found to be the formation of ground-state singlet cyclopropenylidene (c-C 3 H 2 , 1 A 1) by splitting H from cycloprop-2enyl (c-C 3 H 3 , 2 A′). The other reaction mechanisms leading to H 2 CCC(1 A 1) + H, HCCCH(3 B) + H, and H 2 + HCCC(2 Π) exhibit barriers only 1-5 kcal/mol higher than those to produce H + cC 3 H 2. Detailed RRKM calculations will be needed to predict the product branching ratios under various reaction conditions. The C(3 P) + C 2 H 3 reaction channel, yielding intermediate C 3 H 3 radicals on the first excited doublet state PES, is also studied by utilizing the CASSCF(11,11)/6-311+G(d,p) and MRCI+D(7,8)/ANO(2+) levels of theory. Three local minima and six transition states are located on the excited-state C 3 H 3 PES. Various H and H 2 loss channels are studied as well. The C-H fission of H 2 CCCH(1 2 A′′) leading to HCCCH(1 1 A′′) + H is the most energetically favorable channel. Finally, thermochemical parameters for the C 3 H n (n) 1-4) species are determined by employing the G3 theory and the CCSD(T)/6-311+G(3df,2p) method. The differences between the calculated results and available literature data do not normally exceed 1-2 kcal/mol. On the basis of the present calculations and previous theoretical and experimental data, ∆H f o 298 (H 2 CCCH)) 84.5 (1 kcal/mol, ∆H f o 298 (c-C 3 H 3)) 114.5 (2 kcal/mol, ∆H f o 298 (H 3 CCC)) 124 (2 kcal/mol, ∆H f o 298 (c-C 3 H 2)) 118.0 (1 kcal/mol, ∆H f o 298 (H 2 CCC)) 133 (1 kcal/mol, ∆H f o 298 [HCCCH(3 B)]) 132.5 (1 kcal/mol, ∆H f o 298 [HCCCH-(1 A 1)]) 144 (1 kcal/mol, ∆H f o 298 [HCCC(2 Π)]) 173 (2 kcal/mol, and ∆H f o 298 (c-C 3 H)) 170 (2 kcal/ mol are recommended.
The Journal of Physical Chemistry A, 2004
The UV absorption spectrum along with the self-reaction and oxidation reaction kinetics of the hydroxycyclohexadienyl radical, C 6 H 6 OH (which results from OH addition to benzene), were studied using excimer laser photolysis coupled to transient UV absorption. The radicals were generated by photolysis of N 2 O/H 2 O/ C 6 H 6 /He mixtures at 193 nm in a series of chemical reactions initiated by O( 1 D). The radical has continuous absorption in the range 260-340 nm with a maximum absorption cross-section of (8.1 ( 1.4) × 10 -18 cm 2 molecule -1 at 280 nm. Reaction of the radical with molecular oxygen, C 6 H 6 OH + O 2 h C 6 H 6 (OH)OO (1), and self-reaction C 6 H 6 OH + C 6 H 6 OH f products (2), were studied over the 252-285 K temperature range at 1.01 ( 0.02 bar (He). The radical temporal profiles were recorded via transient absorption at 315 nm. In reaction 1, two-time-domain "equilibration" kinetics were recorded in the temperature range 252-273 K. The rate constant of the addition reaction is k 1 ) (1.4 ( 0.8) × 10 -12 exp(-18.6 ( 1.7 kJ mol -1 /RT) cm 3 molecule -1 s -1 . The standard enthalpy of reaction 1 was determined from the measured equilibrium constants using the third law method: ∆H°2 98 ) -43.6 ( 2.0 kJ mol -1 . The measured rate constant of self-reaction 2 is k 2 ) (6 ( 3) × 10 -11 exp(-2.00 ( 1.6 kJ mol -1 /RT) cm 3 molecule -1 s -1 .
Calorimetric and Computational Study of 1, 3, 5-Trithiane
The Journal of …, 2001
To understand the differences in conformational behavior and reactivity of oxygen-and sulfurcontaining 1,3,5-heterocyclohexanes, the enthalpies of formation and sublimation of 1,3,5-trithiane, 1, have been measured. The numerical value of the enthalpy of formation for this compound in the solid state is-8.6 (2.6 kJ mol-1 , while the corresponding value in the gaseous state is 84.6 (2.6 kJ mol-1. The value for the enthalpy of sublimation is 93.2 (0.2 kJ mol-1. Standard ab initio molecular orbital calculations at the G2(MP2), G2, and G3 levels were performed, and the calculated enthalpies of formation are compared with the experimental data. These experimental and theoretical studies support the relevance of through-space lone pair-lone pair electronic repulsion in the sulfur heterocycle.
The Journal of Physical Chemistry, 1992
The kinetics of the reaction between CH3C0 and HBr has been studied using a heatable tubular reactor coupled to a photoionization mass spectrometer. CH3C0 was produced homogeneously by laser photolysis in the presence and absence of HBr. Radical decays were monitored in time-rcsolved experiments. Rate constants were determined at five temperatures in the range 300-400 K and fitted to the Amhenius expression, 6.4 (*3.6) X lO-" exp(4.45 (fl.50) kJ mol-'/RI) an3 molecule-l s-', This kinetic information was combined with known rate constants and Arrhenius parameters for the reverse reaction to obtain the heat of formation of CH3C0. Both m n d law and third law procedures were used to obtain this thermochemical information from these rate constants. The two determinations of this heat of formation were in close agreement (differing by only 0.4 kJ mol-'). These results, taken together, provide a CH3C0 heat of formation of-10.0 f 1.2 kJ mol-' at 298 K which is 14 kJ mol-' higher than the value in common use. The current results imply a CH3-C0 bond enthalpy of 45.1 (f 1. 5) kJ mol-' which is 14 kJ mol-' lower than currently believed and a CH3CO-H bond enthalpy of 373.8 (*1.5) kJ mol-' which is higher by this same figure. Former disparities between reported CH3C0 heats of formation associated with the equilibrium systems studied to obtain this thermochemical information are resolved.