Elucidating the Three‐Dimensional Structure of Piracetam through Rotational Spectroscopy

Herein we report on the most stable structures adopted by piracetam, a nootropic drug, in isolated conditions. A chirped pulse Fourier transform microwave spectrometer (CP-FTMW) coupled with a laser ablation source has been employed to explore the broadband rotational spectrum of piracetam in the 6.0-14.0 GHz range. Two conformers have been observed. The most stable conformer of piracetam adopts an exo configuration of the ring and is mainly stabilized through a N-H⋅⋅⋅⋅⋅⋅O=C hydrogen bond between the amide group and the rings' carbonyl oxygen. The second conformer is close in stability and only differs in the endo disposition of the ring. The results show a low interconversion barrier between both conformers.