Complete experimental and theoretical proton and carbon nuclear magnetic resonance spectral assignments, molecular structure and conformational study of 1-cyclohexylpiperazine and 1-(4-pyridyl)piperazine

The possible stable forms and molecular structures of 1-cyclohexylpiperazine (1-chpp) and 1-(4-pyridyl)piperazine (1-4pypp) molecules have been studied experimentally and theoretically using nuclear magnetic resonance(NMR) spectroscopy. C-13, N-15 cross-polarization magic-angle spinning NMR and liquid phase H-1, C-13, DEPT, COSY, HETCOR and INADEQUATE NMR spectra of 1-chpp (C10H20N2) and 1-4pypp (C9H13N2) have been reported. Solvent effects on nuclear magnetic shielding tensors have been investigated using CDCl3, CD3 OD, dimethylsulfoxide (DMSO)-d(6), (CD3)(2)CO, D2O and CD2Cl2. H-1 and C-13 NMR chemical shifts have been calculated for the most stable two conformers, equatorial-equatorial (e-e) and axial-equatorial (a-e) forms of 1-chpp and 1-4pypp using B3LYP/6-311++G(d,p)//6-31G(d) level of theory. Results from experimental and theoretical data showed that the molecular geometry and the mole fractions of stable conformers of both molecules are solvent dependent. Copyright (c) 2009 John Wiley & Sons, Ltd.