Kinetics of the reactions of methoxy and ethoxy radicals with oxygen

PdII-Catalyzed methoxylation of C(sp3)-H bonds adjacent to benzoxazoles and benzothiazoles

The Pd(OAc)2/PhI(OAc)2 catalyst system promotes the highly regioselective dehydrogenative methoxylation of a C(sp3)-H bond adjacent to benzoxazole and benzothiazole rings. The title transformation constitutes the first example of a Pd-catalyzed C(sp3)-H activating methoxylation at the proximal-selective α-position with regard to a directing auxiliary and provides expedient access to an important class of azole-decorated methyl ethers (up to 90% isolated yield). The synthetic practicality of the methodology was demonstrated by achieving α-methoxyacetic acids via the elimination of the benzoxazole auxiliaries and by obtaining the precursor of an O-methylated Breslow intermediate.

Influence of water on the CH3O˙ + O2 → CH2O + HO2˙ reaction

Electronic structure calculations employing density functional theory have been used to study the effect of a single water molecule on the CH3O˙ + O2 → CH2O + HO2˙ reaction. The investigation suggests that in the presence of water the reaction barrier reduces from 3.01 kcal mol-1 to -1.86 kcal mol-1. Consequently, when we consider the bimolecular rate constants for the water catalyzed channel, they were found to be 104 to 105 times higher than that of the uncatalyzed reaction. Interestingly, the Arrhenius plot indicates a negative temperature dependency of the catalyzed channel (anti-Arrhenius behavior); as a result of this the domination of the catalyzed channel over the bare reaction increases with the lowering of the temperature. But the effective bimolecular rate constant values for the catalyzed channel were found to be approximately four orders of magnitude lower than that of the uncatalyzed one, which implies that the contribution of the catalyzed channels to the overall rate of the reaction is very small.

Revisiting the reaction energetics of the CH3O˙ + O2 (3Σ−) reaction: the crucial role of post-CCSD(T) corrections

The CH₃O˙ + O₂ reaction has been studied by means of high level ab initio calculations to predict the reaction energy and barrier height with chemical accuracy.

Isomerization of methoxy radical in the troposphere: competition between acidic, neutral and basic catalysts

A comprehensive investigation of the roles of acidic, neutral and basic catalysts in isomerization of methoxy radical in the troposphere has been carried out by quantum chemical calculations at the MP2 and CCSD(T) levels of theory.

Atmospheric chemistry of CH3O: its unimolecular reaction and reactions with H2O, NH3, and HF

Herein, we present a definitive example where tunneling plays an important role in hydrogen atom transfer reactions.

Isomerization of the methoxy radical revisited: the impact of water dimers

Investigations carried out at MP2 and CCSD(T) levels of theory show that water dimers can compete with formic and sulfuric acids in catalyzing isomerization of methoxy radicals in the lower troposphere.

Theoretical Mechanistic Study on the Radical−Molecule Reaction of CH2OH with NO2

The complex singlet potential energy surface for the reaction of CH2OH with NO2, including 14 minimum isomers and 28 transition states, is explored theoretically at the B3LYP/6-311G(d,p) and Gaussian-3 (single-point) levels. The initial association between CH2OH and NO2 is found to be the carbon-to-nitrogen approach forming an adduct HOCH2NO2 (1) with no barrier, followed by C-N bond rupture along with a concerted H-shift leading to product P1 (CH2O + trans-HONO), which is the most abundant. Much less competitively, 1 can undergo the C-O bond formation along with C-N bond rupture to isomer HOCH2ONO (2), which will take subsequent cis-trans conversion and dissociation to P2 (HOCHO + HNO), P3 (CH2O + HNO2), and P4 (CH2O + cis-HONO) with comparable yields. The obtained species CH2O in primary product P1 is in good agreement with kinetic detection in experiment. Because the intermediate and transition state involved in the most favorable pathway all lie blow the reactants, the CH2OH + NO2 reaction is expected to be rapid, as is confirmed by experiment. These calculations indicate that the title reaction proceeds mostly through singlet pathways; less go through triplet pathways. In addition, a mechanistic comparison is made with the reactions CH3 + NO2 and CH3O + NO2. The present results can lead us to deeply understand the mechanism of the title reaction and may be helpful for understanding NO2-combustion chemistry.

Laser-Induced Fluorescence Spectra of 4-Methylcyclohexoxy Radical and Perdeuterated Cyclohexoxy Radical and Direct Kinetic Studies of Their Reactions with O2

The laser-induced fluorescence (LIF) excitation spectra of the 4-methylcyclohexoxy and d11-cyclohexoxy radicals have been measured for the first time. LIF intensity was used as a probe in direct kinetic studies of the reaction of O(2) with trans-4-methylcyclohexoxy and d11-cyclohexoxy radicals from 228 to 301 K. Measured rate constants near room temperature are uniformly higher than the Arrhenius fit to the lower-temperature data, which can be explained by the regeneration of cyclic alkoxy radicals from the product of their beta-scission and the effect of O(2) concentration on the extent of regeneration. The Arrhenius expressions obtained over more limited ranges were k(O2) = (1.4(+8)(-1)) x 10(-13) exp[(-810 +/- 400)/T] cm(3) molecule(-1) s(-1) for trans-4-methylcyclohexoxy (228-292 K) and k(O2) = (3.7(+4)(-1)) x 10(-14) exp )[(-760 +/- 400) /T] cm(3) molecule(-1) s(-1) for d11-cyclohexoxy (228-267 K) independent of pressure in the range 50-90 Torr. The room-temperature rate constant for the reaction of trans-4-methylcyclohexoxy radical with O2 (obtained from the Arrhenius fit) is consistent with the commonly recommended value, but the observed activation energy is approximately 3 times larger than the recommended value of 0.4 kcal/mol and half the value previously found for the reaction of normal cyclohexoxy radical with O2.

A Combined Experimental and Theoretical Investigation of the Reactions of 3-Pentoxy Radicals: Reaction with O2 and Unimolecular Decomposition

The reactions of 3-pentoxy radicals with O

In addition to the experimental investigation, the unimolecular reaction channels of 3-pentoxy radicals were also analyzed by a combined