Empirical and estimated values for the free enthalpy

The results shown in Table 2,2.7 were calculated for hypothetical stereospecific polymers in gas form, but the results are in fairly good agreement with the experimental values for the heat of reaction. 

Another procedure to estimate free enthalpies is based on the assumption that the values for AH and AS can be obtained from additive fragment contributions with some corrections due to two centers contributions or other structural factors [3, 6]. This type of procedure (additivity model) uses for the estimation formulas of the form  

Individual values for the heat of formation AH° of fragments in various molecular moieties are given, for example, in [3]. A simplified set of parameters for both heats of formation AH° and for entropies AS° of several common fragments in organic molecules and for some structural factors are given in Tables 2.2.8 and Table 2.2.9, respectively. The resulting values are assumed to give estimations for the compounds in ideal gas form [6]. 

Fragment AH fragment. oO trsgmerc Fragment AH fragment AS fragment 

For free radicals, some group contributions are given in Table 2.2.10. 

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