Proton Transfer in Solid 1-phenyl butane-1,3-dione and related 1,3-diones as studied by 13C CPMAS and AM1 Calculations

ALEJANDRO JOSE VILA; LAGIER, C M; OLIVIERI, A C

JOURNAL OF PHYSICAL CHEMISTRY

AMER CHEMICAL SOC

Año: 1991 vol. 95 p. 5069 - 5073

0022-3654

The intramolecular proton transfer taking place in l-phenylbutane-1,3-dione was studied by using I3C NMR data obtained both in solution and in the solid state. Comparison of CPMAS results with carbon chemical shifts measured in solution reveals that this compound exists in both phases as a rapidly interconverting mixture of both possible enol tautomers, with a slight preference for the methyl keto structure. Semiempirical AM1 calculations support this conclusion, leading to a preferred form having the enolic structure and giving two minima with optimized geometries corresponding to two different enol tautomers having almost equal energy. NMR data are also reported for related 1,3-diaryl-1,3-diketoneisn both phases, which show them to undergo a similar proton-exchange process