Experimental structure of piperonal and the piperonal···neon complex: CP-FTMW spectroscopy.

Piperonal, a bioactive aromatic aldehyde of relevance to the fragrance, food, and pharmaceutical industries, was investigated by high-resolution broadband Fourier transform microwave spectroscopy in a supersonic expansion using neon as carrier gas. Four species were assigned in the 2-8 GHz frequency region, corresponding to two conformers of the piperonal monomer and their respective Ne complexes. The sensitivity of the spectrometer enabled the detection of all heavy-atom isotopologues of the monomer in natural abundance, together with the 22Ne isotopologue of the complexes. The resulting rotational constants allowed the determination of the molecular structures of the monomer and its Ne complexes using the rs and r0 methods. In addition, the potential energy function governing the ring-puckering motion of the 1,3-benzodioxole moiety was characterized. These results provide a detailed description of the intrinsic structure, complexation, and conformational flexibility of piperonal under isolated conditions.