STUDY OF RING-OPENING OF 1,2-DIFORMYL-1,2-DIAZACYCLOBUTENE BY AB-INITIO AND DENSITY-FUNCTIONAL GAUSSIAN-TYPE ORBITAL APPROACH

The conrotatory ring opening of three conformers of 1,2-diformyl-1,2-diazacyclobutene were studied by ab initio and DFT methods. The geometries of the reactants and the corresponding transition state structures were optimized with the RHF/3-21G*, RHF/6-311 + G(d,p), SVWN/6-311 + G(d,p), and BLYP/6-311 + G(d,p) approaches. The activation barrier was calculated at the same theory level and by MP2/6-311 + G(d,p) single point calculation on RHF/6-311 + G(d,p) geometries. For qualitative comparison, the reactivity AM1 semiempirical calculation of bond orders for ab initio and DFT generated geometries was used. It was determined that 1,2-diformyl-1,2-diazacyclobutene will be less reactive toward ring opening than cis-1,2-dihydro-1,2-diazacyclobutene owing to strong hydrogen bonding between the hydrogen of one and the carbonyl of the other formyl group. It was estimated that for other 1,2-diacyl-1,2-diazacyclobutenes the activation energy will be considerably lower because hydrogen bonding stabilization is no longer possible.