Réactions d'addition nucleophile sur les cétones. Influence de l'environnement stérique sur la position de l'état de transition

In the present investigation, we have measured the secondary kinetic deuterium isotope effects in hydroxylamine addition reaction for a series of cyclohexanones, both hindered and unhindered. We observed a slightly direct isotope effect, kH/kD > 1.00, for unhindered cyclohexanones and an inverse isotope effect, kH/kD < 1.00, for hindered cyclohexanones; this inversion of the isotope effects is attributed to a decrease of the torsional strain through the intervention of an “effet sterique de compression” that induce a slight deformation of the cycle and changes the angle of approach of the nucleophile.