Dihedral angle

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

Fluoroformyl Trifluoroacetyl Disulfide, FC(O)SSC(O)CF3: Synthesis, Structure in Solid and Gaseous States, and Conformational Properties#

Abstract: Fluoroformyl trifluoroacetyl disulfide, FC(O)SSC(O)CF3, is prepared by quantitative reaction between FC(O)SCl and CF3C(O)SH. The conformational properties and geometric structure of the gaseous molecule have been studied by vibrational spectroscopy (IR(gas), Raman(liquid), IR(matrix)), gas electron diffraction (GED), and quantum chemical calculations (B3LYP and MP2 methods). The disulfide bond length derived from the GED analysis amounts 2.023(3) A, and the dihedral angle around this bond, φ(CS−SC), is 77.7(21)°, being the smallest dihedral angle measured for noncyclic disulfides in the gas phase. The compound exhibits a conformational equilibrium at room temperature having the most stable form C1 symmetry with a synperiplanar (sp-sp) orientation of both carbonyl groups with respect to the disulfide bond. A second form was observed in IR spectra of the Ar matrix isolated compound at cryogenic temperatures, corresponding to a conformer that possess the carbonyl bond of the FC(O) moiety in antiperiplanar po...

Dependence of the γ carbon‐13 shielding effect on the dihedral angle

Abstract: The γ effects on 13C shielding have been examined for a series of rigid molecules containing the substituents CH3, OH, NH2, F, Cl, Br or I. Plots of the γ effect vs the CC-αC-βX dihedral angle are well scattered if the plots do not distinguish modes of substitution. For the series in which the resonating carbon is CH2, however, fairly linear correlations are observed for XCH3, OH, NH2, Cl and Br. It is concluded that within a structurally defined and substitutionally homogeneous series, there is a reasonably linear stereochemical dependence. Although substitution at C-α does not seriously alter the linear relationship, hybridization of the intermediate carbons may be important. The slopes of the plots for the γ effect vs dihedral angle are remarkably similar. Neither a strictly steric (van der Waals) nor a strictly polar source can be the cause of the linear relationship, since our series of substituents ranges widely with respect to both size and electronegativity. The only two factors that are constant within the series are the removal of the hydrogen atom (CCCH to CCCX) and the addition of the bonding and nonbonding orbitals on X that were not present on H.

Metal complexes of dipyrromethenes linked by rigid spacer arms

Abstract: Metal complexes using ligands where two terminal dipyrromethenes are connected by rigid spacers, having different dihedral angles, show unique macrocyclic structures which contain large cavities in their centers and produce crystals with tunnels of varying structures depending upon their crystal packing motifs.

General Force-Field Parametrization Scheme for Molecular Dynamics Simulations of Conjugated Materials in Solution.

Abstract: We describe a general scheme to obtain force-field parameters for classical molecular dynamics simulations of conjugated polymers. We identify a computationally inexpensive methodology for calculation of accurate intermonomer dihedral potentials and partial charges. Our findings indicate that the use of a two-step methodology of geometry optimization and single-point energy calculations using DFT methods produces potentials which compare favorably to high level theory calculation. We also report the effects of varying the conjugated backbone length and alkyl side-chain lengths on the dihedral profiles and partial charge distributions and determine the existence of converged lengths above which convergence is achieved in the force-field parameter sets. We thus determine which calculations are required for accurate parametrization and the scope of a given parameter set for variations to a given molecule. We perform simulations of long oligomers of dioctylfluorene and hexylthiophene in explicit solvent and f...