Viscosity-Dependent Behavior of Geminate Caged-Pairs in Supercritical Fluid Solvent

Tanko, James M.; Suleman, N. Kamrudin; Fletcher, Beth

doi:10.1021/ja9624174

Cited by 18 publications

(17 citation statements)

References 21 publications

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“…It is worth noting that in this and previous works, Tanko et al [86][87][88] address the important issue of radical/solvent complexation. Complexation may have dramatic influence on selectivity in free radical reactions.…”

Section: Chlorine Atom Cage Effectsmentioning

confidence: 76%

“…Tanko and co-workers have recently reported that SC CO 2 may be used as an environmentally benign alternative to CCl 4 , CFCs, and benzene for free radical bromination reactions. [86][87][88] Reaction yields, times, and selectivities, in SC CO 2 , were found to be analogous to the conventional solvents. Tanko et al 88 have also recently reported the viscosity-dependent behavior of geminate caged pairs in the free radical chlorination of cyclohexane in SC CO 2 .…”

Section: Chlorine Atom Cage Effectsmentioning

confidence: 99%

“…[86][87][88] Reaction yields, times, and selectivities, in SC CO 2 , were found to be analogous to the conventional solvents. Tanko et al 88 have also recently reported the viscosity-dependent behavior of geminate caged pairs in the free radical chlorination of cyclohexane in SC CO 2 . Figure 24 presents the scheme for the photoinduced free radical chain process.…”

Section: Chlorine Atom Cage Effectsmentioning

confidence: 99%

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Homogeneous Organic Reactions as Mechanistic Probes in Supercritical Fluids

1999

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Section: Chlorine Atom Cage Effectsmentioning

confidence: 76%

Section: Chlorine Atom Cage Effectsmentioning

confidence: 99%

Section: Chlorine Atom Cage Effectsmentioning

confidence: 99%

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Homogeneous Organic Reactions as Mechanistic Probes in Supercritical Fluids

1999

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“…To obtain φ pair , 1/ Φ obsd was plotted as a function of viscosity. If φ pair is assumed to be independent of viscosity for a particular solvent system, then the y -intercept of this plot is equal to the reciprocal of φ pair . , This last statement is shown by eq 3: the second term on the right-hand side contains a viscosity dependence such that k cP / k dP becomes much smaller than one as the viscosity approaches zero. Thus, at zero viscosity (infinite fluidity), Φ obsd will equal φ pair .…”

Section: Resultsmentioning

confidence: 98%

Radical Cage Effects in the Photochemical Degradation of Polymers: In-Cage Trapping of Photochemically Generated Radical Cage Pairs in Polymer Model Compounds

et al. 1999

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This study explored the origins of the observation that the overall quantum yields for polymer photodegradation depend on the polymer chain length. The (CH3(CH2) n C(O)NHCH2CH2Cp)2Mo2(CO)6 (n = 3, 8, 13, 18) complexes (1 − 1 − 4 − 4) were synthesized and used as model complexes for the study. As is common for metal−metal bonded complexes of this type, irradiation of these molecules cleaved the metal−metal bonds and formed free radicals via the intermediate formation of a radical cage pair. Studies on previous model complexes showed that the quantum yields for degradation decreased as the chain length of the complex increased. The decrease in quantum efficiency was partially attributed to an increase in the radical cage effect as the chain length increased. Surprisingly, however, the overall quantum yields and cage effects for complexes 1 − 1 − 4 − 4 did not vary significantly with chain length. The similarity in the quantum yields and in the cage effects for these molecules is attributed to an internal trapping reaction of the metal radicals in the solvent cage by the H atom of the amide group. The resulting Mo···(H)−N agostic interaction forms a six-membered ring. The trapping reaction takes place by segmental rotation of the metal-containing end of the radical chain; the rate of this motion is independent of the chain length, and thus differences in the cage effects and the overall quantum yields will be diminished for the four molecules. The X-ray crystal structure of the (CH3(CH2)3C(O)NHCH2CH2Cp)2Mo2(CO)6 molecule is also reported.

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“…The following procedure was employed [50,51]. The appropriate volume of cyclohexane was placed in a 1 mL ampoule.…”

Section: Chlorination Of Cyclohexane In Sccozmentioning

confidence: 99%