AB-INITIO STUDY OF THE POTENTIAL-ENERGY SURFACE OF THE REACTION OF ETHYLENE WITH NITRONIUM ION

The mechanism of the reaction between ethylene and nitronium ion has been investigated theoretically using SCF, SCF/MP2, QCISD, and MCSCF techniques at the 4-31 G and 6-31+G* levels. In addition to the existence and nature of the long-range electrostatic intermediates, reaction paths have been investigated (I) leading to a 1,3 dipolar cycloaddition to yield a five-membered-ring structure, (II) leading to formation of a bridged pi complex, (III) leading to formation of a CNO2 sigma-bonded species and subsequently to a CCNO four-membered-ring cycloadduct, and (IV) leading to formation of an intermediate O-nitroso form. The 1,3 dipolar cycloaddition is shown to be possible from the electrostatic minimum via a small barrier of 3.4 kcal mol-1 at the 6-31+G* QCISD level. At the same computational level, the existence of a bridged pi complex, less than 0.5 kcal mol-I above the long-range electrostatic complex, has been demonstrated. The region of the sigma-bonded species, which lies 2.8 kcal mol-I higher in energy, is a transition-state region for the formation of a CCNO four-membered ring. The formation of the O-nitroso form occurs without any barrier.