Infrared spectra and conformation of substituted 3-benzylidene-2,4-pentanediones

Abstract Fundamental CO and CC stretching frequencies and carbonyl first overtones of substituted 3-benzylidene-2,4-pentanediones were measured in CCl 4 and CHCl 3 . The data are correlated with substituent constants and carbonyl stretching frequencies of corresponding substituted acetophenones. By investigating the effect of substituents, solvents, temperature and anharmonicity as well as the i.r. data of model compounds, the absorption bands were assigned to the vibrations of structural groups. Evidence was obtained that 3-benzylidene-2,4-pentanediones in liquid or solid state and in organic solvents exist in two quasi planar conformations I and II .