Substituted 1-(cyclohexenyl)-3-phenylpropen-1-ones, 1-(2-furyl)-3-phenylpropen-1-ones, and 1-(2-thienyl)-3-phenylpropen-1-ones, ketones with 1,4-pentadien-3-one structure, prefer in solution, and at room temperature, according to 1H NMR and IR investigations the s-trans/s-cis conformation. For some compounds the participation of other conformers in the equilibrium could be demonstrated. These results were obtained by a qualitative study of 25 derivatives in different solvents, and comparison with results from MM+, PM3, AM1 or MMX calculations.