Dihedral angle

About: Dihedral angle is a research topic. Over the lifetime, 15718 publications have been published within this topic receiving 174904 citations.

Switching orientation of two axial imidazole ligands between parallel and perpendicular in low-spin Fe(III) and Fe(II) nonplanar porphyrinates.

Abstract: We have reported here the synthesis, structure, and properties of low-spin bis-imidazole-coordinated Fe(III) and Fe(II) complexes of 5,10,15,20-tetrakis(pentafluorophenyl)-2,3,7,8,12,13,17,18-octachloroporphyrin, [FeIII(TFPPCl8)(L)2]ClO4 and FeII(TFPPCl8)(L)2 (L = 1-methylimidazole, 4-methylimidazole, imidazole). The X-ray structure of FeII(TFPPCl8)(1-MeIm)2 is reported here, which demonstrated the near-perpendicular axial ligand orientation (dihedral angle between two 1-methylimidazoles is 80.7°) for Fe(II) porphyrins in a highly saddle-distorted macrocyclic environment. Oxidation of FeII(TFPPCl8)(L)2 using thianthrenium perchlorate produces [FeIII(TFPPCl8)(L)2]ClO4, which was also isolated in the solid state and characterized spectroscopically. The complex gives rhombic EPR spectra in both solid and solution phases at 77 K and thus represents a rare example of nearly parallel axial ligand orientations for the unhindered imidazoles in a saddle-distorted porphyrin macrocycle. Geometry optimization using D...

Synthesis, Structure, and Electron-Donating Ability of 2,2′:6′,2″-Dioxatriphenylamine and Its Sulfur Analogue

Abstract: 2,2′:6′,2″-Dioxa- and dithia-triphenylamines 4a and 4b were prepared. Both compounds had a C2-like structure. The sulfur compound 4b had a more twisted structure than 4a; the dihedral angle between...

Conformational studies of nucleic acids. II. The conformational energetics of commonly occurring nucleosides.

Abstract: We have examined the conformational energetics of the eight most commonly occurring nucleosides—A, U, G, C, dA, dT, dG, dC—as monitored by a semi-empirical energy force field. These are the first reported calculations to completely explore the entire conformational spaces available to all eight major nucleosides using experimentally consistent furanose geometries and an appropriate force field. Central to our approach is the ability to model an experimentally reasonable furanose for each nucleoside directly from only one parameter, the phase angle of pseudorotation P, as described in the previous paper (D.A. Pearlman, and S.-H. Kim, preceeding paper in this issue). This allows us to specify the conformation of a nucleoside by three variables: torsion angle γ (05′—C5′—C4′—C3′); torsion angle χ (04′—C1′—N9/N1—C4/C2); and P. In our study each of these parameters was allowed to vary independently and in small increments over the range 0–360°. The empirically observed preferences for C3′-endo and C2′-...

Poly(p-phenylene-co-2,5-pyrazine): An AM1 investigation

Abstract: We present an AM1 study of the geometry of some oligomers of a new electrically conductive polymer: the poly(p-phenylene-co-2,5-pyrazine) (PPPz). We examine the evolution of the total energy, the ionization potential and the inter-ring bond length as a function of the torsion angle between adjacent rings. We have also investigated the geometry of charged (ions +1 and −1) oligomers of PPPz. Based on the obtained results we can explain the observed increase in the conductivity for PPPz induced by p doping and we suggest a way of increasing its value.