Molecular structures of N-ethylpiperidine betaine hydrate and its 1:1 complex with squaric acid

Authors:

• Z. Dega-Szafran,
• Grzegorz Edward Dutkiewicz,
• Z. Kosturkiewicz,
• M. Szafran

Abstract

N-ethylpiperidine betaine, (N-carboxymethyl-N-ethylpiperidinium inner salt, EtPB) crystallizes as a hydrate. EtPB and water molecules are bonded by intermolecular OHâ̄O hydrogen bonds of 2.817(1) and 2.863(1) Å, into a centrosymmetric dimer, in which only one carboxylate oxygen atom is involved in H-bonds formation. In the complex of EtPB with squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione, H₂SQ) both carboxylate oxygen atoms are engaged in the hydrogen bonds which links molecules through two short, non-symmetric OHâ̄O hydrogen bonds of 2.489(1) and 2.500(1) Å. The preferences of the conformation of the EtPB unit in the hydrogen bond formation have been studied by X-ray diffraction, FTIR and NMR spectroscopy and the results are supported by DFT calculations. EtPB, in hydrate and in the complex, has a chair conformation with the CH₃CH₂ group in the axial position and the CH₂COO substituent in the equatorial position. © 2013 Elsevier B.V. All rights reserved.