Experimental and theoretical study of N-(2-hydroxyethyl)morpholine betaine

Abstract

N-(2-hydroxyethyl)morpholine betaine (HEMB) has been characterized by a single crystal X-ray analysis, FTIR spectroscopy and DFT calculations. The crystals are monoclinic, space group P2 1/c with a=10.273(2), b=9.360(2), c=9.447(2) Å and β=104.72(3)Å. Two molecules of HEMB form a centrosymmetric dimer ( X2) connected by a pair of hydrogen bonds between the CH 2CH 2OH and COO − groups, with the O⋯O distance of 2.672(2) Å. The morpholine ring adopts a chair conformation with the CH 2CH 2OH group in the axial and the CH 2COO − group in the equatorial position. The structures of the dimer, B2, and two monomers, B1a and B1b, have been optimized by the B3LYP approach using the 6-31G(d,p) basis set. The computed structure of B2, agrees well with the experimental X2. From two stable monomeric conformers the more favored is B1a, with the intramolecular hydrogen bond with the O–H⋯O distance of 2.566 Å. The effects of hydrogen bonding and electrostatic interactions on the conformation of the molecules investigated have been discussed. The FTIR spectrum shows a broad absorption in the 3300–2600 cm −1 region, typical of moderate O–H⋯O hydrogen bonds.