title: Conformational flexibility of mephenesin.
abstract: The mephenesin molecule (3-(2-methylphenoxy)propane-1,2-diol) serves as a test bank to explore several structural and dynamical issues, such as conformational flexibility, the orientation of the carbon linear chain relative to the benzene plane, or the effect of substituent position on the rotational barrier of a methyl group. The molecule has been studied by rotational spectroscopy in the 4-18 GHz frequency range by Fourier-transform methods in a supersonic expansion. The experiment has been backed by a previous conformational search plus optimization of the lowest energy structures by ab initio and density functional quantum calculations. The three lowest-lying conformers that can interconvert to each other by simple bond rotations have been detected in the jet. Rotational parameters for all structures have been obtained, and methyl torsional barriers have been determined for the two lowest-lying rotamers. The lowest-lying structure of mephenesin is highly planar, with all carbon atoms lying nearly in the benzene ring plane, and is stabilized by the formation of cooperative intramolecular hydrogen bonding. An estimation of the relative abundance of the detected conformers indicates that the energetically most stable conformer will have an abundance near 80% at temperatures relevant for biological activity.
authors.affiliation: Departamento de Química Física, Facultad de Ciencia y Tecnología, Universidad del País Vasco (UPV/EHU) , Campus de Leioa, Ap. 644, E-48080 Bilbao, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Écija
authors.forename: Luca
authors.initials: L
authors.lastname: Evangelisti
authors.forename: Montserrat
authors.initials: M
authors.lastname: Vallejo
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Basterretxea
authors.forename: Alberto
authors.initials: A
authors.lastname: Lesarri
authors.forename: Fernando
authors.initials: F
authors.lastname: Castaño
authors.forename: Walther
authors.initials: W
authors.lastname: Caminati
authors.forename: Emilio J
authors.initials: EJ
authors.lastname: Cocinero
mesh_terms: D005583:Fourier Analysis; D006860:Hydrogen Bonding; D008615:Mephenesin / Q000737:chemistry*; D008872:Microwaves; D008968:Molecular Conformation; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D008615:Mephenesin