An Ab initio theoretical study of the eliminative ring fission in cyclopropylmethanide and cyclobutylmethanide

Abstract

Ab initio computations of the eliminative ring fission of cyclobutylmethanide and cyclopropylmethanide have been performed by completely optimizing the stable geometrical structures of the cyclic and open-chain minima as well as the transition structures for ring opening. These results show that the transition state for the four-membered ring opening occurs later (in a geometrical sense) along the reaction path than for the three-membered ring opening, and that the difference in activation energy is negligibly small. The strain energy of cyclobutylmethanide is nearly equal to cyclopropylmethanide, but is released more gradually during the opening of the four-membered ring. The acceleration of ring fission due to ring strain is substantial and of comparable magnitude in the two ring openings, corresponding to a release of about three fourths of the initial strain energy in the transition states.