R : B ratios

The magnetically induced changes in the R(B) ratios observed in the employed solvents were not proportional to but they were almost saturated at 1.75 T. 

Figure 4.3. R B ratios of fission products as a function of their decay constants (Neeb, 1971)...

Figure 4.7. R B ratios of fission product iodine isotopes as a function of the decay constant in the case of the simultaneous presence of fuel rod defects and uranium contamination PWR primary coolant...

Let us consider cases 1-3 in Fig. 4.4. In case 1, AG s for formation of the competing transition states A and B from the reactant R are much less than AG s for formation of A and B from A and B, respectively. If the latter two AG s are sufficiently large that the competitively formed products B and A do not return to R, the ratio of the products A and B at the end of the reaction will not depend on their relative stabilities, but only on their relative rates of formation. The formation of A and B is effectively irreversible in these circumstances. The reaction energy plot in case 1 corresponds to this situation and represents a case of kinetic control. The relative amounts of products A and B will depend on the heights of the activation barriers AG and G, not the relative stability of products A and B. 

Keeling, C.D., Bacastow, R.B. and Tans, P. 1980 Predicted shift in the C/ C ratio of atmospheric carbon dioxide. Geophysical Research Letters 7 505-508. 

Entry R. r2 Alkyne Conditions Support t(h) Products Yield (%) a b ratio... 

Silacyclopentanes (A) were the principal products in every case. The A/B ratio varied with R from a high of 22 when R2 = Ph2 to a low of 4 when R2 = Cl2 (see Table I). 

Overall yields 50-60%. A B ratio refers to Scheme 7.23.b Ratios given in parentheses refer to reaction with CCI,CMe,OH.r Mixture of 6- and 7-substituted compounds. 

Cyclopropane R R2 Y X % yield of acetylenic acetal A B ratio (Scheme 9.5) ... 

In 1999, Clennan and Sram reported a study of the photo-oxidations of a series of tetrasubstituted alkenes (Fig. 5) in methylene blue-doped zeolite Y [11], The ene regiochemistries are very sensitive to the size of the allylic substituent, R, in solution. The A/B ratio increases from 0.49 to 2.4 as the substituent, R, is changed from methyl to ferr-butyl. This phenomenon has been attributed [12] to a sterically induced lengthening of the carbon-2 oxygen bond in the perepoxide intermediate I and subsequent preferred opening of this long bond (Fig. 5). 

The steric effect observed in solution should be amplified in the zeolite if either of the models depicted in Fig. 4 operate because the sodium counterion should force the allylic substiment R to reside to an even greater extent on the face approached by singlet oxygen. This should lead to an increase in allylic hydroperoxy A at the expense of B in stark contrast to the experimental observation (e.g., the A/B ratio does not increase, but actually decreases from 2.4 to 1.58... 

X R Isomeric ratio % Yield Major fraction b.p. no yi (mleY... 

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