GAS-PHASE BASE-CATALYZED CLAISEN-SCHMIDT REACTIONS OF THE ACETONE ENOLATE ANION WITH VARIOUS PARASUBSTITUTED BENZALDEHYDES

Substituent effects were determined for the gas-phase base-catalyzed C laisen-Schmidt reaction of the acetone enolate anion and various para- substituted benzaldehydes. Under chemical ionization conditions, the a dduct for the reaction was detected and the fraction of adduct that is tetrahedral was determined. The Hammett constants for the substituent s correlate the fraction of the adduct population that is tetrahedral. The fraction of tetrahedral intermediate is greatest for those system s in which the negative charge is most highly stabilized. The structur es of the adducts are determined on the basis of collisionally activat ed decomposition mass spectra. These spectra show that both the adduct s of the ion-molecule reactions and deprotonated reference compounds, which have a structure that is similar to the tetrahedral intermediate , decompose by elimination of water and by a retro-aldol reaction. The adducts formed from the ion-molecule reactions show a greater propens ity to reform the acetone enolate, whereas the deprotonated reference compounds eliminate H2O readily. The reaction constant p from the Hamm ett correlation is +1.6, which substantiates that the production of te trahedral intermediates is facilitated by electron-withdrawing substit uents.