Ab initio and empirical computations of mechanism and stereoselectivity
A-t - Over the last few years, we have explored the use of theory to understand mechanisms of organic reactions and the various types of selectivities which they exhibit. Examples described in this lecture will include the Diels-Alder reaction, whose rates were studied quantitatively in 1964 by Sauer's group. Ab initiQ transition structures have been located for the reactions of butadiene with ethylene, acrylonimle, maleonitrile, vinylidene cyanide, acrolein, and acrolein coordinated to a Lewis acid, BH3. Further insights into conformation preferences of conformationally free dienophiles, the degree of asynchronicity induced by substituents, and the origin of & stereoselectivity are discussed. The mechanism of the ketene-ethylene reaction and that of several substituted cases is discussed.