Search results for "Internal rotation"
showing 6 items of 6 documents
17O NMR and molecular mechanical studies of arylmethylenemalonaldehydes
1990
The 17O NMR spectra of six different arylmethylenemalonaldehydes were measured for various solvents and temperatures. The 17O NMR chemical shifts and line widths of the carbonyl oxygens of the malonaldehyde fragment show a clear variation in the series of monoaryl compounds studied. The differences between the 17O NMR chemical shifts of the formyl oxygens correlate well with two conformationally dependent 1H–1H and 1H–13C coupling constants for the same compounds. Molecular mechanical calculations were also performed in order to relate the present data with the conformational preferences of the malonaldehyde fragment of the arylmethylenemalonaldehydes.
Die Primärstabilität von manuell und roboterassistiert implantierten Hüftendoprothesenstielen: eine biomechanische Untersuchung an Kunstfemora
2004
AIM We investigated the initial stability of cementless stems implanted with robotic milling and conventional manual broaching. METHODS Proximally porous structured stems (G2, ESKA-Implants, Luebeck, Germany) were implanted into synthetic femora. In one group, the femoral cavity was prepared by a CT-based robot (CASPAR, URS-Ortho, Germany) with a high-speed milling head. In the other group, femora were rasped manually with broaches. The broaches had 1 mm proximal press-fit, the robotic cavities 1.5 mm. The implants were exposed to 15 000 loading cycles with 1 000 +/- 500 N. The direction of forces on the implant head were chosen to simulate stair climbing. Internal rotation and translation …
Ab initio SCF and CI calculations on the barrier to internal rotation of 1,3-butadiene
1972
Ab initio SCF and CI calculations employing a set of gaussian lobe functions have been carried out for the ground and excited states of five geometrical C4H6-structures occurring in the course of rotation from cis-butadiene to the trans-isomer. The rotational potential curves are discussed for the ground and excited states. Particularly the potential curve of the lowest triplet state is considered in this connection thereby substantiating quantitatively the proposed mechanism for induced dimerisation of C4H6. Possible assignments of the lowest singlet excited states in trans-butadiene are discussed.
Nicethamid‐Analoge, V Untersuchungen zur gehinderten internen Rotation bei N , N ‐Dimethylpyridinamiden
1975
Die Synthese von homologen, vinylogen und Kernalkylierten N,N-Dimethylnicotinamiden wird beschrieben und die Energiebarriere bei der gehinderten Rotation der Amidgruppe mittels 1H-NMR-Spektroskopie bestimmt. Nicethamide Analogues, V. Investigations of Hindered Internal Rotation in N,N-Dimethylpyridinamides The synthesis of homologue, vinylogue and ringalkylated N,N-dimethyl nicotinamides is described and the energy barrier of the hindered rotation of the amide group determined by means of 1H-n. m. r. spectroscopy.
Difficulties of density functional theory in predicting the torsional potential of 2,2?-bithiophene
1998
The internal rotation of 2,2′-bithiophene was investigated within the density functional theory (DFT) approach. Fully optimized DFT torsional potentials are compared with Moller–Plesset (MP2) results which predict a fourfold potential with s-cis- and s-trans-gauche minima. DFT calculations fail in describing the energetics of the internal rotation because they favor planar vs. perpendicular conformers. Gradient-corrected functionals provide torsional potentials where the gauche minima have almost vanished and the s-ciss-trans interconversion barriers are twice as high as the barriers obtained at the MP2 level. The use of local functionals augments the shortcomings of the DFT approach. The g…
Internal rotation of 1,2-dichloroethane in haloalkane dehalogenase. A test case for analyzing electrostatic effects in enzymes
2003
1,2-Dichoroethane (DCE) is a prototypical molecule for studying electrostatic solvent effects on molecular conformation as far as rotation around the carbon−carbon bond notably changes the electric...