title: Delicate balance of hydrogen bonding forces in D-threoninol.
abstract: The seven most stable conformers of D-threoninol (2(S)-amino-1,3(S)-butanediol), a template used for the synthesis of artificial nucleic acids, have been identified and characterized from their pure rotational transitions in the gas phase using chirped-pulse Fourier transform microwave spectroscopy. D-Threoninol is a close analogue of glycerol, differing by substitution of an NH2 group for OH on the C(β) carbon and by the presence of a terminal CH3 group that breaks the symmetry of the carbon framework. Of the seven observed structures, two are H-bonded cycles containing three H-bonds that differ in the direction of the H-bonds in the cycle. The other five are H-bonded chains containing OH···NH···OH H-bonds with different directions along the carbon framework and different dihedral angles along the chain. The two structural types (cycles and chains of H-bonds) are in surprisingly close energetic proximity. Comparison of the rotational constants with the calculated structures at the MP2/6-311++G(d,p) level of theory reveals systematic changes in the H-bond distances that reflect NH2 as a better H-bond acceptor and poorer donor, shrinking the H-bond distances by ∼0.2 Å in the former case and lengthening them by a corresponding amount in the latter. Thus revealed is the subtle effect of asymmetric substitution on the energy landscape of a simple molecule, likely to be important in living systems.
authors.affiliation: Department of Chemistry, University of Pittsburgh , Pittsburgh, Pennsylvania 15260, United States.
authors.forename: Vanesa
authors.initials: V
authors.lastname: Vaquero-Vara
authors.forename: Di
authors.initials: D
authors.lastname: Zhang
authors.forename: Brian C
authors.initials: BC
authors.lastname: Dian
authors.forename: David W
authors.initials: DW
authors.lastname: Pratt
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Zwier
mesh_terms: D000605:Amino Alcohols / Q000737:chemistry*; D002072:Butylene Glycols / Q000737:chemistry*; D003198:Computer Simulation; D006860:Hydrogen Bonding; D008872:Microwaves; D008956:Models, Chemical; D015394:Molecular Structure; D012399:Rotation; D013057:Spectrum Analysis
chemical_list: D000605:Amino Alcohols; D002072:Butylene Glycols; C532652:threoninol