Dihedral angle

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

Molecular and electronic structures of heteroaromatic oligomers : model compounds of polymers with quantum-well structures

Abstract: Conformational preferences of 2,2‘-bithiophene, 2-(2-thienyl)pyrrole, and N-methyl-2-(2-thienyl)pyrrole have been investigated by means of computational methods. Calculations were performed at the ab initio HF/6-31G(d) and MP2/6-31G(d) levels and, additionally, with the density functional B3-LYP/6-31G(d). The results indicate that 2-(2-thienyl)pyrrole behaves similarly to the 2,2‘-bithiophene. Thus, two minimum energy conformations were found for each compound, which correspond to anti-gauche and syn-gauche. Such minima are separated by barriers of about 1.7 and 1.3 kcal/mol at the HF and MP2 levels. On the contrary, the preferences found for N-methyl-2-(2-thienyl)pyrrole were different, giving an almost negligible energy barrier between the two minimum energy conformations. Furthermore, at the MP2 level the anti-gauche and syn-gauche minimum energy conformations present an inter-ring dihedral of 135° and 68°, respectively, displaying deviations greater than those found in 2,2‘-bithiophene and 2-(2-thieny...

Molecular structure and conformation of ethyl methyl ether as studied by gas electron diffraction.

Abstract: The bond distances (rg) and angles (rα) in ethyl methyl ether have been determined by gas electron diffraction as follows: average of C(methyl)–O and C(methylene)–O=1.418±0.002 A, C–C=1.520±0.004 A, C–H=1.118±0.004 A, ∠C–O–C=111.9±0.5°, ∠O–C–C=109.4±0.3°, ∠H–C–H=109.0±0.4°, where uncertainties represent estimated limits of experimental error. The two rg(C–O) distances have been estimated independently with the aid of the rotational constants for the trans conformer reported by Hayashi et al.: C(methyl)–O=1.413±0.009 A and C(methylene)–O=1.422±0.007 A. The dihedral angle for the gauche conformer, 84±6°, and the relative abundance of the trans and gauche conformers in the gas phase at 20 °C, nt⁄(nt+ng)=0.80±0.08, have also been determined.

Raman and Density Functional Study of the S0 State of Phenothiazine and the Radical Cation of Phenothiazine

Abstract: Raman spectra of phenothiazine and its radical cation were obtained. Hartree−Fock (HF) and density functional theory (DFT) ab initio calculations were performed to find optimized structures and computed vibrational frequencies. The ab initio structures are compared to previously reported X-ray diffraction experimental results, and the vibrational frequencies are compared to Raman spectra given here as well as previously reported Raman spectra. We have made vibrational assignments for the observed Raman bands, based on the computed potential energy distribution (PED) and isotopic shifts. Our results indicate that the neutral phenothiazine molecule has a nonplanar structure with ∼153° dihedral angle and the radical cation has a planar (or near planar) structure with ∼180° dihedral angle.

Control over Excited State Intramolecular Proton Transfer and Photoinduced Tautomerization: Influence of the Hydrogen-Bond Geometry

Abstract: The influence of H-bond geometry on the dynamics of excited state intramolecular proton transfer (ESIPT) and photoinduced tautomerization in a series of phenol-quinoline compounds is investigated. Control over the proton donor-acceptor distance (dDA ) and dihedral angle between the proton donor-acceptor subunits is achieved by introducing methylene backbone straps of increasing lengths to link the phenol and quinoline. We demonstrate that a long dDA correlates with a higher barrier for ESIPT, while a large dihedral angle opens highly efficient deactivation channels after ESIPT, preventing the formation of the fully relaxed tautomer photoproduct.