Parametrization of MMX force field for benzocyclobutenes

Abstract

A detailed geometrical analysis of cyclobuta[a], dicyclobuta[a,c], dicyclobuta[a,d] and tricyclobuta[a,b,cl benzenes by molecular mechanics MMX force field has been performed. Results obtained by optimizing the geometries of mentioned compounds by means of the authentic MMX force field have shown that it has to be modified. A parameterization of the MMX force field has been performed by correcting the parameters for the <i>sp³ </i>C-atoms attached to the benzene ring. Compared to the original MMX force field, the modified version reproduces the geometries of benzocyclobutenes with much greater accuracy and reliability, comparable to those for higher-level <i>ab initio </i>methods. The Mills-Nixon effect (weak but not negligible) is also successfully reproduced. We hope that such modified force field can be successfully used for determining the geometries of various cyclosubstituted benzenes and similar compounds.