Theoretical Approaches for Chemical Pyrolytic Reactions

One theoretical approach for the calculation of certain thermodynamic properties of molecules is the use of semiempirical (MO) calculations. As an example, the heat of 

One advantage of these theoretical calculations is that the values can be calculated at different temperatures. This allows a better utilization of the data for the estimation of the values to be utilized in pyrolytic processes. Table 3.7.1 gives some data regarding experimental and calculated heats of formation for several organic radicals using three semiempirical MO parameterizations in MOPAC [27], namely PM3, MNDO and AMI. As seen from Table 3.6.1, vinyl and allyl radicals show the best match. Calculations for molecules containing it electrons and especially those with aromatic character show a better agreement with experimental data. 

Radical Exp. AHf (A ) kcal Calc. AHf (A ) kcal Difference PM3 kcal Difference MNDO kcal Difference AMI kcal 

An example of a theoretical calculation is shown below for an isoprene trimer. The three main possible paths for the formation of radicals, as shown in Section 2.6, are a scission  

The calculated heats of formation and the bond dissociation energies are given in Table 3.7.2. The calculations were done using MOPAC 7 with AM1 Hamiltonian for two different temperatures [32], 

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