Long-range 1 H, 19 F and 13 C, 19 F coupling constants and molecular orbital computations as indicators of internal motion in C 6 H 5 OCF 3 and its 4-fluoro derivative
1991; NRC Research Press; Volume: 69; Issue: 7 Linguagem: Inglês
10.1139/v91-155
ISSN1480-3291
AutoresTed Schaefer, Glenn H. Penner, Rudy Sebastian, James Peeling, Christian Beaulieu,
Tópico(s)Molecular spectroscopy and chirality
ResumoInternal rotational potentials for rotation about the Csp 2 —O bond in C 6 H 5 OCF 3 and its 4-fluoro derivative are computed at the STO-3G and 3-12G levels of molecular orbital theory. As for anisole, the perpendicular conformer is calculated as least stable for C 6 H 5 OCF 3 but the height of the internal barrier is considerably lower than in anisole. The 4-fluoro substituent reduces the twofold component significantly, indicating reduced p …π conjugation, but does not much change the values of the higher terms in the theoretical potentials. The internal potentials are rather flat with minima between about 30° and 45°, these angles measuring the twist away from planarity. The 1 H, 13 C, and 19 F nuclear magnetic resonance spectra in polar and nonpolar solution yield long-range coupling constants, n J( 1 H, 19 F) and n J( 13 C, 19 F). These parameters are qualitatively consistent with relatively low barriers to rotation about the Csp 2 —O bonds in these molecules and with only a small dependence on solvent polarity. Key words: C 6 H 5 OCF 3 and 4-F-C 6 H 4 OCF 3 : 1 H NMR, 19 F NMR, conformations, MO computations.
Referência(s)