Experimental and theoretical NMR study of 4-(1-pyrrolidinyl)piperidine

Abstract

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. ¹H, ¹³C, ¹⁵N, 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 ⁿJ(C,H) (n = 1, 2, 3) coupling constants of 4-pypp have been determined with selective ¹H decoupled ¹³C NMR techniques. ¹H, ¹³C, ¹⁵N NMR chemical shifts and ^1-3J(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.

KEY WORDS: 4-(1-Pyrrolidinyl)piperidine, NMR, DFT, Axial, Equatorial

Bull. Chem. Soc. Ethiop. 2011, 25(3), 437-442.