The conformation of the naproxen anion studied by H-1 NMR and theoretical methods

The conformation of naproxen and the importance of intramolecular hydrogen- bond-like (HBL) C-H . . .O-C interactions was studied by means of the ab in itio HF/6-31G*, HF/3-21G* and semiempirical AM1 methods. Molecular structur e optimisation including rotations around single bonds of naphthalene subst ituents. allowed us to find four stable conformers for which HBL interactio n plays an important role. For all the four conformers the methoxy group is coplanar with the naphthalene ring. Conformational equilibrium related to the internal rotations was also studied by H-1 NMR spectroscopy. The experi mental NOE values as well as coupling constants (3)J(C,H) were compared wit h the calculated values. (C) 2001 Elsevier Science B.V. All rights reserved .