Photo-CIDNP Studies of 2-Butanone and 3-Pentanone in Solution

Abstract

SHIV P. VAISH, ROBERT D . MCALPIKE, and MICHAEL COCIVERA. Can. J. Chem. 52, 2978Chem. 52, (1974. The results of photolysis of 2-butanone and 3-pentanone as studied by chemically induced dynamic nuclear polarization (CIDNP) and electron spin resonance spectroscopy (e.s.r.) are reported. In aqueous solutions and t-butanol only the ethyl radical is detected by means of e.s.r., indicating r cleavage to be a major path involving excited states. This observation is further supported by the n.m.r. spectra which are obtained during irradiation of these ketones in D 2 0 and a mixture of CD,CN-D,O (1: 1 by volume) containing carbon tetrachloride. Several compounds are detected with their protons spin polarized. A mechanism involving radical reactions is proposed which is consistent with the experimental results. Chem. 52, 2978Chem. 52, (1974. On rapporte les resultats de la photolyse de la butanone-2 et de la pentanone-3 tels qu'etudies par polarisation nucleaire dynamique induite chimiquement (CIDNP) et par spectroscopic de resonance paramagnetique electronique (r.p.e.). En solution aqueuse et dans le tevt-butanol on ne detecte par r.p.e, que des radicaux ethyles indiquant que le clivage a est une route importante pour les etats excites. Cette observation est corroboree par des donnees de r.m.n. obtenues durant l'irrad~ation de ces cetones dans D,O ct dans un melange de CD,CN-D20 (I :I par volume) contenant du tetrachlorure de carbone. On dktecte plusieurs composCs ayant des protons avec des spins polarises. On propose un mecanisme impliquant des reactions radicalaires; ce mecanisme est en accord avec les donnees expCrimentales.[Traduit par le journal] Introduction In our earlier paper ( I ) we reported the results of photolysis of acetone as studied by chemically induced dynamic nuclear polarization (CIDNP). In this case, a cleavage and intermolecular hydrogen abstraction involving the triplet state of acetone were the main photochemical reactions responsible for the CIDNP effects. The present study is an extension of our earlier work t o other ketones, namely 2-butanone and 3-pentanone, to ascertain if a cleavage and hydrogen abstraction steps occur for these systems also. In this paper, we report CIDNP evidence which supports the occurrence of the a-cleavage step. We obtained no evidence in support of hydrogen-abstraction step.Experimental