Z. Dega‐Szafran, Z. Kosturkiewicz, E. Nowak
Aug 1, 2002
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0
Influential Citations
13
Citations
Journal
Journal of Molecular Structure
Abstract
Abstract The 1-piperidineacetic acid was synthesized as monohydrate and its structure has been determined by X-ray diffraction methods. The crystals are orthorhombic, space group P212121, a=6.7693(7), b=10.816(1), c=11.452(1) A , Z=4, R=0.037. The acid molecule appears in the zwitterionic form with two equivalent carboxylic oxygen atoms. The water molecules link carboxylic groups into infinite chains parallel to the z axis, by O–H⋯O hydrogen bonds of the lengths 2.85(2) and 2.75(2) A. The N+(1)–H proton forms bifurcated hydrogen bond intramolecular with O(1) and intermolecular with O(2′) of the length 2.795(2) and 2.775(3) A, respectively. Five of the most stable conformers of 1-piperidineacetic acid and four of its monohydrate were analyzed by B3LYP/6-31G(d,p) calculations. For anhydrous acid, NPA1 conformer with intramolecular N⋯H–O hydrogen bond is the most stable. The structure of conformer NPA1 is similar to that of the most stable conformer of N,N-dimethylglycine. The zwitterionic form, ZPA1, is stabilized by the electrostatic interaction between the positively charged N+H and negatively charged oxygen atoms of COO− group. ZPA1 is less stable than NPA1 and the energy difference between them is 23.8 kcal/mol. In the case of monohydrate the difference is only 4.6 kcal/mol. This indicates that addition of water molecule increases the stability of the zwitterionic form of 1-piperidineacetic acid, ZPAW3.