Standard Enthalpies of Formation of 2,6-Di-tert-butyl4-methylphenol and 3,5-Di-tert-butylphenol and Their Phenoxy Radicals

The standard (p^o = 0.1 MPa) enthalpies of formation of 2,6-di-tert-butyl-4-methylphenol and 3,5-di-tert-butylphenol in the gaseous phase, –315.5 ± 4.4 kJ mol^–1 and –312.7 ± 4.6 kJ mol^–1, respectively, were derived from the standard enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry, and from the standard enthalpies of sublimation, at 298.15 K, measured by Calvet microcalorimetry. The O—H bond dissociation enthalpies in those compounds were determined in benzene by photoacoustic calorimetry, leading to the standard enthalpies of formation of the gaseous phenoxy radicals: –189 ± 8 kJ mol^–1 and –154 ± 6 kJ mol^–1, respectively. These results were used to calculate enthalpies of substituent redistribution reactions, which are proposed as a method to estimate new data for substituted phenols.     

Ab initio multireference investigation of disjoint diradicals: singlet versus triplet ground states

We present improved virtual orbital (IVO) complete active space (CAS) configuration interaction (IVO‐CASCI) and IVO‐CASCI‐based multireference Møller–Plesset perturbation theory (MRMPPT) calculations with an aim to elucidate the electronic structure of tetramethyleneethane (TME) in its lowest singlet and triplet state and to quantify their order and extent of splitting. The potential surfaces of singlet and triplet states for the twisting of TME are also studied. We found that the triplet state is higher in energy than the singlet one in the whole range of twisting angles with the energy gap minimum at a twisting angle of about 45°. Harmonic vibrational frequencies of TME have also been calculated for both the states. We also report the ground to first excited triplet state transition energies. Our results are analyzed with respect to the results available in the literature to illustrate the efficacy of our methods employed. We also demonstrate that the spin character of the ground state of disjoint, TME‐like diradicals can be manipulated by using appropriate selection of annulenic spacer to separate the allyl groups of TME.     

Reaction of an Aza[60]fullerene radical with diphenylmethanes and fluorenes: a mechanistic approach

[reaction: see text] The mechanism of the reaction of azafullerene radical C(59)N(*) with diphenylmethane and 9-methyl-9H-fluorene has been investigated. The primary and secondary kinetic isotope effects provide strong evidence for a stepwise mechanism in which the hydrogen-atom abstraction is the rate-determining step.     

Why Aren't There Any Trioxygenyl or Ozonium Salts? Or,Why Does Our Reaction of O3 and PtF6 Give O2PtF6?

The reaction of ozone and gaseous platinum hexafluoride led to O₂PtF₆(s) and not the desired O₃PtF₆(s). Suggestions as to why the synthesis of O₃PtF₆(s) failed are made in terms of the known chemistry of the gaseous O ₃ ⁺ cation with O ₊ ⁵ proposed as an intermediate.     

The gas-phase reaction between O3 and HO radical: a theoretical study.

We report a theoretical study on the reaction of ozone with hydroxyl radical, which is important in the chemistry of the atmosphere and in particular participates in stratospheric ozone destruction. The reaction is a complex process that involves, in the first stage, a pre-reactive hydrogen-bonded complex (C1), which is formed previous to two transition states (TS1 and TS2) involving the addition of the hydroxyl radical to ozone, and leads to the formation of HO4 polyoxide radical before the release of the products HO2 and O2. The reaction is computed to be exothermic by 42.72 kcal mol(-1), which compares quite well with the experimental estimate, and the energy barriers of TS1 and TS2 with respect to C1 are computed to be 1.80 and 2.26 kcal mol(-1) at 0 K. A kinetic study based on the variational transition state theory (VTST) predicts a rate constant, at 298 K, of 7.37 x 10(-14) cm3 molecule(-1) s(-1), compared to the experimentally recommended value of 7.25 x 10(-14) cm3 molecule(-1) s(-1).     

脉冲光声量热法测量 n-C_4H_9Co(Salen)H_2O的Co-C键离解能

时间可分辨的脉冲光声量热法(Ｔｉｍｅｒｅｓｏｌｖｅｄｐｕｌｓｅｄｐｈｏｔｏａｃｏｕｓｔｉｃｃａｌｏｒｉｍｅｔｒｙ,ＰＡＣ)是一种能在纳秒至微秒的时间尺度内研究由激光诱导的光化学和光生物学反应的有效方法［１～５］。我们利用光声量热检测系统测量了席夫碱类型的辅酶Ｂ１２模型化合物ｎＣ４Ｈ９Ｃｏ（Ｓａｌｅｎ）Ｈ２Ｏ的Ｃｏ-Ｃ键离解能,得到了有意义的结果。１实验实验中激发源为波长３５５ｎｍ的脉冲激光(脉冲宽度８ｎｓ,重复频率１０Ｈｚ),采用的量热参比为二茂铁(Ｆｅｒｒｏｃｅｎｅ)甲醇溶液,它在３５５ｎｍ处的吸光度与样…     

Analyzing Reaction Rates with the Distortion/Interaction‐Activation Strain Model

The activation strain or distortion/interaction model is a tool to analyze activation barriers that determine reaction rates. For bimolecular reactions, the activation energies are the sum of the energies to distort the reactants into geometries they have in transition states plus the interaction energies between the two distorted molecules. The energy required to distort the molecules is called the activation strain or distortion energy. This energy is the principal contributor to the activation barrier. The transition state occurs when this activation strain is overcome by the stabilizing interaction energy. Following the changes in these energies along the reaction coordinate gives insights into the factors controlling reactivity. This model has been applied to reactions of all types in both organic and inorganic chemistry, including substitutions and eliminations, cycloadditions, and several types of organometallic reactions.     

Theoretical investigation of the structures and properties of fluoromethyl peroxyl radicals

The equilibrium geometries, harmonic vibrational frequencies, charge distributions, spin density distributions, dipole moments, electron affinities (EAs), and C? O bond dissociation energies (BDEs) of HO, CH₃O, CH₂FO, CHF₂O, and CF₃O peroxyl radicals have been calculated using ab initio molecular orbital theory and density functional theory (DFT) at the B3LYP level. The C? H bond dissociation energies of the parent fluoromethanes have been calculated using the same levels of theory. Both the MP2(full) and B3LYP methods, using the 6‐31G(d,p) basis set, are found to be capable of accurately predicting the geometries of peroxyl radicals. Electron correlation accounts for ～25% of the C? H BDE of fluoromethanes and for ～50% of the C? O BDE of the corresponding peroxyl radicals. The B3LYP/6‐31G(d,p) method is found to be comparable to high ab initio levels in predicting C? O BDEs of studied peroxyl radicals and C? H BDEs of the parent alkanes. The progressive fluorine substitution of hydrogen atoms in methyl peroxyl radicals results in shortening of the C? O bond, lengthening of the O? O bond, an increase (decrease) of the spin density on the terminal (inner) oxygen, a decrease in the dipole moments, and an increase in electron affinities. Both C? O BDEs and EAs of peroxyl radicals (RO) correlate well with Taft σ* substituent constants for the R group in peroxyl radicals. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004