Portal de Periódicos da CAPES

NMR Chemical Shifts. 1. The Role of Relative Atomic Orbital Phase in Determining the Sign of the Paramagnetic Terms: ClF, CH 3 F, CH 3 NH 3 + , FNH 3 + , and HC⋮CF

1998; American Chemical Society; Volume: 102; Issue: 45 Linguagem: Inglês

10.1021/jp982214x

1520-5215

Kenneth B. Wiberg, Jack D. Hammer, Kurt W. Zilm, James R. Cheeseman, Todd A. Keith,

Chemical Thermodynamics and Molecular Structure

The shielding of several nuclei for molecules in magnetic fields was examined via B3LYP/6-311+G(3df,3pd) calculations using the MP2/6-31G* geometries. Both the gauge-invariant atomic orbital (GIAO) and individual gauges for atoms in molecules (IGAIM) methods were employed, and the molecules were the isoelectronic series F2, ClF, CH3F, CH3NH3+, FNH3+, and FC⋮CH. The main paramagnetic contributions arose from the π and π' molecular orbitals (MOs) interacting with the σ* MO. The π interaction leads to deshielding in all cases. However, for the π' MO in which the two p atomic orbitals have opposite phase, one nucleus is deshielded but the other is shielded. This appears to be a general phenomenon.