C-13 CP MAS NMR, FTIR, X-ray diffraction and PM3 studies of some N-(omega-carboxyalkyl)morpholine hydrohalides

N-(omega -carboxyalkyl)morpholine hydrochlorides, OC4H8N(CH2)(n)COOH . HCl, n = 1-5, were obtained and analyzed by C-13 cross polarization (CP) magic angle spinning (MAS) NMR, FTIR and PM3 calculations. The structure of N-(3- carboxypropyl)-morpholine hydrochloride (n = 3) has been solved by X-ray di ffraction method at 100 K and refined to the R = 0.031. The crystals are mo noclinic, space group P2(1)/c, a = 14.307(3), b = 9.879(2), c = 7.166(1) An gstrom, beta = 93.20(3)degrees, V = 1011.3(3) Angstrom (3), Z = 4. In this compound the nitrogen atom is protonated and two molecules form a centrosym metric dimer, connected by two N+-H . . . Cl- (3.095(1) Angstrom) and two O -H . . . Cl- (3.003(1) Angstrom) hydrogen bonds. C-13 CP MAS NMR spectra, c ontrary to the solution, showed non-equivalence of the ring carbon atoms. T he PM3 calculations predict a molecular dimer without proton transfer for a n HCl complex, while for an HBr complex an ion pairs with proton transfer, and reproduces correctly the conformation of both dimers but overestimates H-bond distances. Shielding constants calculated from the PM3 geometry of i on pairs gave a linear correlation with the C-13 chemical shifts in solids. (C) 2001 Elsevier Science B.V. All rights reserved.