EXPERIMENTAL AND THEORETICAL NMR STUDY OF 4-(1-PYRROLIDINYL)PIPERIDINE

The possible stable forms and molecular structure of 4-(1-pyrrolidinyl)piperidine (4-pypp) have been studied experimentally and theoretically using nuclear magnetic resonance (NMR) spectroscopy. H-1, C-13, N-15, DEPT, COSY and HETCOR NMR spectra of 4-pypp (C9H18N2) have been reported. Solvent effects on nuclear magnetic shielding tensors have been investigated using chloroform-d, methanol-d, acetone-d, dimethylsulfoxide-d and water-d. The magnitude of (n)J(C,H) (n = 1, 2, 3) coupling constants of 4-pypp have been determined with selective H-1 decoupled C-13 NMR techniques. H-1, C-13, N-15 NMR chemical shifts and (1-3)J(C,H) coupling constants have also been calculated for the most stable two conformers, equatorial-equatorial (e-e) and axial-equatorial (a-e) forms of 4-pypp using DFT/6-311++G(d,p)//6-31G(d) level of theory. Results from experimental and theoretical data have showed that the molecular geometry and the mole fractions of stable conformers of 4-pypp are solvent dependent.