THEORETICAL-STUDIES OF SUBSTITUENT EFFECTS ON STATIONARY STRUCTURES OF AMIDINE DECOMPOSITION

The unimolecular decomposition of substituted acetamidines XC(=NH)NH2, where X = CH3(I), CH2F (II), CHF2 (III), CF3 (IV), CH2NH2 (V) and CH2NO2 (VI) has been examined by ab initio methods using the 4-31G standard basis set. The process has an asynchronous mechanism. Transition structures for all the compounds can be described as four-membered rings. The influence of substitution on the decomposition process is discussed in terms of a modified version of a More O'Ferrall-Jencks type diagram. The effects of functional groups are larger in a perpendicular than a parallel orientation to the reaction path; this is an example of the 'anti-Hammond' effect.