Modeling a reaction path by molecular mechanics: Dimerization of carbon free radicals

✍ Scribed by Anusch Peyman; Hans-Dieter Beckhaus

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 718 KB
• Volume: 13
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.540130502

✦ Synopsis

A variable force field model for radical dimerization was developed. It uses MM2 force constants for most atoms and new parameters only for the core atoms involved in bonding changes. The change in hybridization from sp2 to sp3 is modeled using distance-dependent switch functions. The validity of the model has been tested by calculating the minimum energy path of the dimerization of di-tert-butylmethyl radicals. The calculated and experimental values for the enthalpy of activation of both dimerization of the radicals and dissociation of the dimer are in excellent agreement. The model has also been successfully applied to the stereoselective dimerization of 1-phenylneopentyl radicals: The form of the potential energy surface yields an explanation for the observed stereoselectivity. Another common feature in radical dimerization seems to be the formation of adsorption complexes prior to dimerization that can lead to increased reactivity. The results suggest that it is important to analyze the whole reaction path and not only the transition state alone.