Detail of "2324-98-3"

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Molecular Structure and Internal Rotation in 2,3,5,6-Tetrafluoroanisole as Studied by Gas-Phase Electron Diffraction and Quantum Chemical Calculations

Molecular Structure and Internal Rotation in 2,3,5,6-Tetrafluoroanisole as Studied by Gas-Phase Electron Diffraction and Quantum Chemical Calculations. Belyakov, Alexander V.; Kieninger, Martina; Cachau, Raul E.; Ventura, Oscar N.; Oberhammer, Heinz (St. Petersburg State Technological Institute, St. Petersburg 190013, Russia). Journal of Physical Chemistry A, 109(2), 394-399 (English) 2005 American Chemical Society. CODEN: JPCAFH. ISSN: 1089-5639. DOCUMENT TYPE: Journal CA Section: 22 (Physical Organic Chemistry) The geometric structure of 2,3,5,6-tetrafluoroanisole and the potential function for internal rotation around the C(sp2)-O bond were detd. by gas electron diffraction (GED) and quantum chem. calcns. Anal. of the GED intensities with a static model resulted in near-perpendicular orientation of the O-CH3 bond relative to the benzene plane with a torsional angle around the C(sp2)-O bond of t(C-O) = 67(15)°. With a dynamic model, a wide single-min. potential for internal rotation around the C(sp2)-O bond with perpendicular orientation of the methoxy group [t(C-O) = 90°] and a barrier of 2.7 ± 1.Several substances like 2324-98-3 may be metioned in this study.6 kcal/mol at planar orientation [t(C-O) = 0°] was derived. Calcd. potential functions depend strongly on the computational method (HF, MP2, or B3LYP) and converge adequately only if large basis sets are used. The electronic energy curves show internal structure, with local min. appearing because of the interplay between electron delocalization, changes in the hybridization around the oxygen atom, and the attraction between the pos. polarized hydrogen atoms in the Me group and the fluorine atom at the ortho position. The internal structure of the electronic energy curves mostly disappears if zero-point energies and thermal corrections are added. The calcd. free energy barrier at 298 K is 2.0 ± 1.0 kcal/mol, in good agreement with the exptl. detn. .

Comparison of large basis set DFT and MP2 calculations in the study of the barrier for internal rotation of 2,3,5,6-tetrafluoroanisole

All Rights Reserved. Comparison of large basis set DFT and MP2 calculations in the study of the barrier for internal rotation of 2,3,5,6-tetrafluoroanisole. Kieninger, Martina; Cachau, Raul E.; Oberhammer, Heinz; Ventura, Oscar N. (Detema, Facultad de Quimica, CCPG, Montevideo 11800, Urug.). International Journal of Quantum Chemistry, Volume Date 2007, 107(2), 403-417 (English) 2006 John Wiley & Sons, Inc. CODEN: IJQCB2. ISSN: 0020-7608. DOCUMENT TYPE: Journal CA Section: 22 (Physical Organic Chemistry) Section cross-reference(s): 65 The barrier for internal rotation around the -OCH3 bond in 2,3,5,6-tetrafluoroanisole was calcd. using the d. functional theory (DFT) and second-order Moller-Plesset (MP2) methods with Pople's basis sets up to 6-311++G(3df,2p) and Jensen basis sets up to pc-3. The results are converged only if fairly large basis sets are used (at least 6-311++G(3df,2pd) or pc-2). Both the DFT and MP2 potential energy curves show internal structure. Two min. and three maxima are obsd. on the curves, arising from the interplay between lone-pair delocalization and changes in the hybridization around the oxygen atom, together with the attraction between the pos. polarized hydrogens in the Me group and the neg. polarized fluorine atom at the ortho position. These crit. points are somehow ironed out by the addn. of zero-point and thermal corrections to the energy curves. At this level, the MP2 method can describe reasonably well the previously detd. single-well exptl. rotational barrier, 2.7 ± 2.0 kcal/mol at 298 K, while all DFT methods yield a much smaller result. 2324-98-3 which is the cas registry number of some chemical is mentioned. As obsd. exptl., the -OCH3 group is perpendicular to the aryl ring in the equil. structure, although two very close min. with an intermediate hump at 90° are still observable. The theor. free energy barrier of rotation at the MP2(full)/pc-2 level is 2.0 ± 1.0 kcal/mol, in reasonable agreement with the exptl. detn. .