Comparative study of the 3-phenylcoumarin scaffold: Synthesis, X-ray structural analysis and semiempirical calculations of a selected series of compounds

Compounds 1 (6-methyl-3-phenylcoumarin), 2 (3-(o-methoxyphenyl)-6-methylcoumarin) and 3 (3-(m-methoxyphenyl)-6-methylcoumarin) were synthesized by a Perkin reaction between the 2-hydroxy-5-methylbenzaldehyde and the corresponding phenyl acetic acid. 1H and 13C NMR and X-ray diffractometry determined the molecular structures of the derivatives. A comparative study between compounds 1, 2 and 3, based on the structural results, was carried out. In addition, the X-ray structures were compared to those obtained combining conformational analysis with semiempirical methodologies (AM1 and PM3). The results provided by the semiempirical calculations in gas phase are in strong agreement with the X-ray method for the three molecules under study, meaning that the determination of the 3D structure for this type of compounds could be extrapolated from semiempirical studies.