On thermal reaction

Fig. 3. Arrhenius plot for reaction (5a). O From photochemical experiments23 A based on thermal reaction data.

In 1973, Sagdeev et al. [16] reported MFEs on thermal reactions of substituted benzyl chlorides (ACl) with n-butyl lithium (BLi) in hot hexane and cyclohexane. Although there were many serious misprints in this paper, this was the first report for MFEs on chemical reactions through radical pairs. The reactions occur through the following scheme ... 

Magnetic Field Effects on Thermal Reactions through Biradicals... 

Cyclt iopenone ketals (35) on thermal reaction give ir-delocalized singlet vinylcarbenes (36c), which serve as thim-carbon 1,1-A, 3-dipoles (36a) lacking octet stabilization that cycloadd to a-pyrones effectively. ... 

To investigate the route to polycyclic compounds, the experiments were carried out on thermal reactions of benzene to diphenyl, of benzene with butadiene and of styrene with ethylene to Tetralin isomers, and of cyclohexene with butadiene to octalin. However, the rates of these reactions were too small to account for the formation of polycyclics in thermal reactions of both ethylene and propylene. The obtained result leads to the speculation that some reactive radicals should play an important role in polycyclic formation. 

Y.-B. Xiang, S. Drenkard, K. Baumann, D. Hickey and A. Eschenmoser, Chemistry of a-amino-nitriles. 12. Exploratory experiments on thermal-reactions of a-amino-nitriles, Helv. ChimicaActa, 1994, 77, 2209-2250. 

Photosubstitution of [Mo(CO)5(PPh3)] leads to CO loss ( 366nm=0.58) in preference to PPhs loss ( 366nm = 0.11). The equilibrium of cis- and trans-[Mo(CO)4(PPhs)2] leads to a photochemical stationary state in favour of the thermodynamically less stable cw-isomer, and evidence is given for a facile conversion of the unsaturated C4 -isomer of [Mo(CO)4(PPh3)j into the Cs-isomer, substantiating observations made on thermal reactions. ... 

For the pyrolysis of paraffinic hydrocarbons at 700- 800 C, yields of olefins such as ethylene, propylene, butenes, butadiene and cycloolefins increase during the initial stage of the reaction, pass through their maxima, and later decrease yields of aromatics, hydrogen and methane however increase monotonically throughout the reaction course. Sakai et al. (1 ) reported previously the result of a kinetic study on thermal reactions of ethylene, propylene, butenes, butadiene and these respective olefins with butadiene at the conditions similar to those of paraffin pyrolysis, directing their attention on the rates of formation of cyclic compounds. Kinetic features of the thermal reactions of these olefins are sunnnarized in Table I combined with the results obtained in later investigations for thermal reactions of cycloolefins ( 2) and benzene O). 

Work on thermal reactions between perfiuoroazomethane and methane (at 347.5 °C) or di-t-butyl peroxide (at 170 °Q at temperatures above and below, respectively, that at which the azo-compound fragments to provide trifluoromethyl radicals, has shown that the azo-compound is an unusually good methyl-radical trap. Thermal decomposition of 2,2 -diphenyl-2,2 -... 

NMR of 7a with TfOH showed that at -40°C complex 7a led to the formation of an alkenylcarbyne complex 32 by protonation of the aUenylidene P-carbon (Scheme 22). This species was found to be catalytically inactive for a test RCM reaction. On rising the temperature to -20°C the species 32 releases its proton and afforded the indenyhdene-ruthenium complex 33 that could be further isolated. The complex 33 resulted from an intramolecular rearrangement and was revealed as the active species (Scheme 22) die complex 33 was identified to the species formed from 7a on thermal reaction. 

Several theoretical studies have been performed on thermal reactions. Ab initio electronic-structure calculations at the 6-3IG level have been performed to determine the mechanism of the thermal isomerization of buta-1,2-diene to buta-1,3-diene. The thermal interconversion of the norbornadiene and quadricyclane radical cations has been studied, with geometries optimized at the UMP2/6-31G and UHF/6-31G levels. Two transition structures are proposed with C and C2 symmetry, respectively. They conclude by suggesting the true transition state is the Ci symmetric one whereas the second is a second-order saddle point. The thermal rearrangement of diformyl peroxide has been studied using the UHF/AMl MO method to determine the mechanism of the isomerization and the MP2 method to improve the barrier energies of the reaction. A stepwise radical reaction is proposed. ... 

Cis- and trans-siilbenc oxides 92 undergo photochemical ring opening due to a C—C bond scission. The resulting singlet or triplet state can be trapped with MA to yield the anhydride 93. Geometric considerations for the product have been discussed.A similar product is known to form on thermal reaction (see Chapter 7). 

Influence of Molecular Interaction on Thermal Reaction Power... 

In the early 1990s, the derivatization of fullerenes was based on thermal reactions, e.g., the Diels-Alder reaction of Cso with substituted dienes leading to cyclohexyl-fused fullerene derivatives, and only a few examples were known, where a fullerene adduct was obtained by photochemical reactions. The pioneering work in the field of photochemical derivatization of fullerenes was done by Wilson, Schuster, and colleagues who, for example, reported the [2 + 2]-photocycloaddition of enones to CgQ. Nowadays, more and more fullerene derivatives are synthesized by photochemical reaction pathways. 

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