Studies of the mechanisms of some organic reactions and photoreactions by semiempirical SCF MO methods

Abstract

Applications of MINDO/3 and MNDDO/2 (an analogous version of NDDO) over the last two years are summarized. (a) Calculations for 185 reactions have led to certain conclusions concerning the requirements that must be satisfied if theoretical calculations of reaction mechanisms are to be significant. Examples of the unfortunate effects of failure in these respects are cited. (b) MINDO/3 calculations of molecular vibration frequencies and isotopic frequency shifts, entropies, specific heats, entropies of activation, and kinetic isotopic effects have given results in good agreement with experiment. (c) Calculations for π cycloaddition reactions confirm our earlier conclusion that such reactions are two-step processes. (d) A number of ene reactions have been found to be synchronous. (e) The mechanisms of several reactions involving 1,2 elimination of hydrogen from positive ions have been studied. (f) Detailed calculations of the C₇H⁺₇ and C₇H⁺₈ potential surfaces gave results in good agreement with mass spectral evidence. (g) S_N2 reactions, carbonyl addition reactions, and reactions of carboxylic acid derivatives, with anionic nucleophiles, are predicted to require no activation in the gas phase. (h) A study of the triplet di-π-methane rearrangement of 1,5-hexadiene has led to an interpretation of the reaction that agrees well with experiment.