title: Temperature effects on the hydrogen-bond patterns in 4-piperidinecarboxylic acid.
abstract: A temperature-controlled X-ray powder diffraction experiment, complemented with TGA and DSC analysis, allowed us to follow changes in the molecular conformation and hydrogen-bond patterns of 4-piperidinecarboxylic acid. The presence of three phases is confirmed. Phase 1 represents the monohydrated form of 4-piperidinecarboxylic acid, which exists from room temperature to 359 K, where dehydration occurs. Phase 2 measured at 363 K corresponds to an anhydrous form of the acid. At ca 458 K the onset of a second, more gradual transition is observed, which ends at around 543 K. Phase 3 measured at 543 K is a high-temperature anhydrous form of the acid. The structures of phases 2 and 3 were solved from synchrotron powder diffraction data by simulated annealing using the DASH program and refined by the Rietveld method. The phase changes are accompanied by modification of the hydrogen-bond patterns and of the torsional orientation of the terminal carboxylate group. This group makes a 49 degrees rotation about the C1-C2 bond during the first transition.
authors.affiliation: Laboratorio de Cristalografía, Departamento de Química, Facultad de Ciencias, Universidad de Los Andes 5101, Venezuela. asiloe@ula.ve
authors.forename: Asiloé J
authors.initials: AJ
authors.lastname: Mora
authors.forename: Edward E
authors.initials: EE
authors.lastname: Avila
authors.forename: Gerzon E
authors.initials: GE
authors.lastname: Delgado
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Fitch
authors.forename: Michela
authors.initials: M
authors.lastname: Brunelli
mesh_terms: D002152:Calorimetry, Differential Scanning; D002264:Carboxylic Acids / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D044367:Phase Transition; D010880:Piperidines / Q000737:chemistry*; D013696:Temperature; D013818:Thermogravimetry; D014961:X-Ray Diffraction
chemical_list: D002264:Carboxylic Acids; D010880:Piperidines; C502346:4-piperidinecarboxylic acid