Quantum-chemical, NMR and X-ray diffraction studies on (±)-1-[3,4-(methylenedioxy)phenyl]-2-methylaminopropane

Time-averaged conformations of ( )-1-[3,4-(methylenedioxy)phenyl]-2-methylaminopropane hydrochloride (MDMA, ‘‘ecstasy’’) in D2O, and of its free base and trifluoroacetate in CDCl3, were deduced from their 1H NMR spectra and used to calculate their conformer distribution. Their rotational potential energy surface (PES) was calculated at the RHF/6-31G(d,p), B3LYP/6-31G(d,p), B3LYP/cc-pVDZ and AM1 levels. Solvent effects were evaluated using the polarizable continuum model. TheNMR and theoretical studies showed that, in the free base, the N-methyl group and the ring are preferentially trans. This preference is stronger in the salts and corresponds to the X-ray structure of the hydrochloride. However, the energy barriers separating these forms are very low. The X-ray diffraction crystal structures of the anhydrous salt and its monohydrate differed mainly in the trans or cis relationship of the N-methyl group to the a-methyl, although these two forms interconvert freely in solution.This work was supported by Proyecto INI 06/03-2 Universidad de Chile, Proyecto Conicyt Bicentenario de Insercion Academica-2004, FONDECYT grant 2000009, the Presidential Chair in Sciences (BKC), and ICM grant no. P99- 031-F (Chile), and FAPESP and CNPq (Brazil). YPM and JE are grateful to CNPq for research fellowships