Dear Sir;

among the most involved people in the study of the free radical chemistry and physics;  Prof. Hans Fischer (died in 2006) worked extensively in this area; so I recommend to go through his work. Regards

Thank you for the idea

Dear Gyorgy, 

Are you restricted to use AM1 for geometry optimizations? I have doubts that semiemprical parameters are really well defined enough to describe radicalic properties...

I have a benchmark study here, maybe you can have a look if you decide to make your minimization calculations using other methods (higher levels):

https://www.researchgate.net/publication/236015813_Role_of_Chain_Transfer_Agents_in_Free_Radical_Polymerization_Kinetics

Something less broad in terms of methodology, but a reaction of interest closer to yours is:

https://www.researchgate.net/publication/229497689_Cyclization_Tendencies_in_the_Free_Radical_Polymerization_of_Allyl_Acrylate_Derivatives_A_Computational_Study

I can also suggest you these publication here:

https://www.researchgate.net/publication/258801539_A_computational_approach_to_the_free_radical_polymerization_kinetics_of_alkyl_a-hydroxymethacrylate_monomers_A_structure-reactivity_relationship

https://www.researchgate.net/publication/272407326_Relationship_Between_the_Free_Radical_Polymerization_Rates_of_Methacrylates_and_the_Chemical_Properties_of_their_Monomeric_Radicals?ev=prf_pub

I hope these give you some more idea,

Best,

Ilke

Article Role of Chain Transfer Agents in Free Radical Polymerization Kinetics

Article Cyclization Tendencies in the Free Radical Polymerization of...

Article A computational approach to the free radical polymerization ...

Article Relationship Between the Free Radical Polymerization Rates o...

Dear Ilke,

Thank you for the rich reference list. No, I am not constrained in geometry optimization but AM1 optimization is faster and in certain cases I tried to use ab initio geometry optimization without getting much more convincing results. I thought that it is enough to increase the level of energy calculation. if you wish to perform the calculation on several compounds or on larger monomers, you have to look for faster/cheaper methods. Of course, if the cheaper approximation does not yield acceptable results one either pays the price in calculation time or gives up and uses a more empirical approach based on experimental data - wherever available. Anyway, I will study your references. Thanks again. Gyorgy

Dear Gyorgy, I have been working on free-radical polymerization reaction kinetics of acrylates and methacrylates science 2005 and unfortunately I have to say that I can not rely on the AM1 results anymore even for conformation analysis for the monomers. Many times, I experienced weird attractions between Hydrogen atoms on Carbon atoms. As semi-empiric methods, AM1, PM3 and PM6 show this kind of problem. Therefore, I can not recommend semi-empiric methods for even conformer search analysis. It is well known that DFT methods are really good for geometry optimization and frequency calculations. B3LYP/6-31G(d) or better one is M06-2x/6-31G(d) can be suggested. For the masterpiece reference for the free radical addition reactions "Fischer, H., Radom, L. (2001). Factors controlling the addition of carbon-centered radicals to alkenes - a experimental and theoretical perspective. Angewandte Chemie: International Edition, 40, 1340-1371." If you interested in acrylates and methacrylates, may be this old paper can be helpful https://www.researchgate.net/publication/236015651_Density_Functional_Theory_Study_of_Free-Radical_Polymerization_of_Acrylates_and_Methacrylates_Structure-Reactivity_Relationship

We used also some semi-empiric calculations in this study however generated conformers have to be checked carefully.   

I hope this explanation is a little bit helpful.

Best regards

Isa

Data Density Functional Theory Study of Free-Radical Polymerizati...