INDEX of reactions

Comprehensive Organic Chemistry , Pergamon, Elmsford, NY, 1979, is a six-volume treatise on the synthesis and reactions of organic compounds. The first three volumes cover the various functional groups, vol. 4, heterocyclic compounds, and vol. 5, biological compounds such as proteins, carbohydrates, and lipids. Probably the most useful volume is vol. 6, which contains formula, subject, and author indexes, as well as indexes of reactions and... 

For further examples of the indexes of reaction see Section I,H. More complicated is the triplet reaction with the index... 

In this rate law, n is called the index of reaction, and it usually has values of 1.5, 2, 3, or 4. These rate laws are generally abbreviated as A1.5, A2, etc. In particular, the A1.5 rate law (when = 1.5, l/ is 2/3, so this rate law is sometimes identified in that way) has been used to describe crystaUization processes in some soHds. The rate laws having n = 2 and n = 3 are associated with two- and three-dimensional growth of nuclei, respectively. 

Another conclusion can be illustrated by studying Figure 7.3. If only a few data points were available and if they were subject to substantial errors, as they frequendy are for soHd state reactions, it would be difficult (if not impossible) to determine the correct index of reaction. Also, some other... 

While this procedure may certainly give an optimum value of n with respect to the Hnearity of the/(a,T) versus 1/T plot, the order determined may have no relationship to the molecularity of a transition state in the usual kinetic sense. The n value is usually called the index of reaction. In most cases, the results obtained from this type of analysis are similar to the kinetic parameter determined by conventional isothermal means, and in many cases the agreement is excellent. However, it must be remembered that the original rate law is assumed to have the form... 

From the data shown in Table 8.2, it is clear that the value of Ta/R is constant only for the correct value of n (in this case, 5/3 or 1.667). It is also clear that for small values of a, the value of Ea/R does not change much regardless of the value chosen for n. The first step in the analysis is to compute an approximate value for Ea/R. and this is performed using two data pairs, (ai,Ti) and (ct2,T2), where a and 2 are small. The Ea/R is nearly constant for any value of n under these conditions. The first value assigned to the index of reaction, is zero, and a reasonably accurate value of Ea/R results with as long as a and 2 are small (see rows 1 and 2 of the Ea/R values shown in Table 8.2). For the first two data pairs, the value of Ea/R varies only from 11,646 to 12,140 as n varies from 0.4 to 2. 

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