REACTION OF CCL2 WITH CH2NH AND THE FORMATION OF DIPOLAR AND BIRADICAL YLIDE STRUCTURES

The potential energy surface for the reaction between CH2NH and CCl2 h as been investigated using ab initio methods. We have performed geomet ry optimizations at the MP2/6-31G level of theory and single point ca lculations at the MP4(SDQ)/6-311+ +G* level. The reaction step for yl ide formation has a free energy of activation predicted to be 5.0 kcal mol(-1). The parallel 1,2-cycloaddition reaction has a calculated fre e energy barrier of 16.5 kcal mol(-1), indicating that this second pat hway is not competitive with ylide formation. The structure of the azo methine ylide formed in the first reaction step is similar to that fou nd for the ylide resulting from the reaction of methylene with ammonia and corresponds to a dipolar species, This is highly unstable and rea rranges to its more stable isomer, the biradical azomethine ylide, whi ch has a structure similar to the corresponding carbonyl ylide. This s pecies has a free energy barrier to ring closure calculated to be 21.2 kcal mol(-1), so it has reasonable kinetic stability, The resulting a ziridine has a free energy of 24.1 kcal mol(-1) lower than the biradic al azomethine ylide, and the activation free energy of ring opening is calculated to be 45.3 kcal mol(-1).